Author: Sarvan Kumar

Sarvan Kumar http://sarvankumar.wordpress.com My name is Sarvan Kumar, I am post graduate in chemistry (MSc). besides teaching chemistry at various schools and coaching centres I have been giving home tuitions to students for 10 years. I have helped students score good marks in chemistry not only in board examination but also JEE, NEET, SAT, IGCSE and IB examinations. Nearly 90% of my students have scored more than 95% in their CBSE board examination. Moreover they have also secured a seat in prestigious engineering and medical college. Since every student is different hence my unique style of teach

Chemistry Notes Chemical bonding and molecular structure

Chemical bonding and molecular structure

Define chemical bond.

The attractive force of attraction which holds the atoms together in a molecule called chemical bond.

What is octet rule?

Atoms can combine either by transfer of valance electrons from one atom to another or by sharing of valance electrons in order to have an octet in their valance shell.

How does ionic bond form explain with example?

Ionic bond forms by transfer of valance electron from one atom to another.

Example:Formation of NaCl

(i)Loss of an electron by Na metal and formation of cations.

(ii) Gain of an electron by Cl nonmetal and formation of anions

(iii)The negative anion and positive cation forms NaCl by electrostatic force of attraction.

Define electrovalent bond.

The electrostatic force of attraction between cation and anion which holds the ion together in a molecule is called electrovalent bond.

Define electrovalency.

The number of electrons loss or gain by elements in particular ionic compound is called electrovalency.

Example:NaCl

Electrovalencey of Na =1

Electrovalencey of Cl =1

Explain formation of covalent bond with example.

Covalent bond forms by sharing of electrons between two atoms.

Example formation of H₂O.

Define covalency.

Number of electrons an atom can share with other atoms is called covalency.

Example: In H₂O Covalency of H=1,and covalency of oxygen is 2

The drawback of octet theory.

(i) Octet rule is based upon the chemical interest of noble gases .However some noble gases also form some compound.

(ii)Octet rule does not explain the shape of the molecules.

(iii) It does not explain the relative stability of the molecules.

Describe the factors for formation of ionic compound.

(i) Metals which form cation must have low ionization enthalpy.

(ii)Non metals which form anion must have high electron gain enthalpy.

(iii)Lattice enthalpy of ionic compound should be high.

Define lattice enthalpy.

Energy require to separate one mole of a solid ionic compound into gaseous constituent ions is called lattice enthalpy.

Define bond order.

Number of bonds between two atoms in a molecule is called bond order.

Define bond length.

Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule.

Define covalent radius.

The covalent radius is half of the distance between two similar atoms joined by a covalent bond in a same molecule.

Define van der Waals radius.

Half of the distance between two similar atoms in a separate molecule.

Define bond angle.

Angle between the orbitals containing bonding electron pairs around the central atom in molecule.

Define Bond enthalpy.

Energy required to break one mole of bonds of a particular type between two atoms in a gaseous state.

Define average bond enthalpy.

Average bond enthalpy in a polyatomic molecule can be obtained by dividing total bond dissociation enthalpy by number of bonds broken.

Explain formal charge.

Formal charge =[Total number of valence electrons in the free atom]-[Total number of nonbonding electrons( lone pair electrons)]-1/2[Total number of bonding (shared electrons) electrons]

What are the limitations of octet rule?

(i)The incomplete octet of the central atom.

(ii )Odd –electron molecules.

(iii)The expanded octet

Draw Lewis dot structure of following compound.

C₂H₄

N₂

H₂

O₂

O₃

NF₃

CO₃^2-

H₂O

CCl₄

Lewis dot structure of carbon tetrachloride

PCl₅

Lewis dot structure of phosphorus pentachloride

SF₆

Lewis dot structure of sulphur hexachloride

H₂SO₄

CH₄

NH₄⁺

SO₂

NH₃

SF₄

Lewis dot structure of sulphur tetrafluooride

ClF₃

BrF₅

XeF₄

NO₃ ^–

What is Fajan’s Rule?

The partial covalent character of ionic bond was discussed by Fajan’s,by following rules.

(i)The smaller the size of cation and the larger the size of anion the greater the covalent character of particular ionic bond.

(ii)The greater the charge on the cation the greater the covalent character if the ionic bond.

Explain VBT with example.

(i)Covalent bond between two atom forms by overlapping of atomic orbitals.

(ii)Only valence shell orbitals can take part in bonding and must have opposite spin.

(iii)Greater the overlap the stronger is the bond formed between two atoms.

Example : Formation of H₂ molecule.

H₂

Electronic configuration of one H atom 1s¹

Shape of s orbital

Overlapping

Thus H-H forms, having one bond

Explain the formation of following molecules on the basis of VBT.

N₂

Electronic configuration of one N atom 1s²,2s²,2p³

Shape of three p orbitals

Overlapping

O₂

Electronic configuration of one O atom 1s²,2s²,2p⁴

Shape of two p orbitals

Overlapping

Thus O=O forms having one sigma and one pi bond.

Mention two types of overlapping and nature of covalent bond.

There are two types of bond formed during overlapping of atomic orbitals.

(i)Sigma bond( Covalent bond which forms by head on overlapping along the intermolecular axis.

Following types of overlapping can form sigma bond

(i)s-s overlapping.

(ii)s-p overlapping.

(iii)p-p overlapping.

(iii )Pi Bond( Covalent bond forms by side on overlapping .

Following types of overlapping can form pi bond.

(iii)p-p overlapping.

Which bond is stronger in sigma and Pi bond?

Sigma bond is stronger bond than Pi bond because in case of sigma bond the overlapping of orbitals takes place to a larger extent.

What are the main postulates of VSEPR theory.

(i) Electron pair Geometry of the molecule is decided by both bond pair and lone pair orbitals ,but Molecular geometry of the molecules is decided by only bond pair orbitals.

(iii)The repulsive interaction of electrons pair decreases in the following order.

Lone pair(lp)-lone pair(lp) > Lone pair(lp)-bond pair(bp) > bond pair(bp)-bond pair(bp)

What are the steps to find shape of the molecules according to VSEPR theory.

Example: NH₃

Step (i)Write Lewis dot structure of NH₃.

Step(ii)Chose central atom here it is N

Step(iii)Find bond pair orbitals and lone pair orbitals

bp=3,lp=1

Step(iv)Find the sum of lp and bp

Here lp+bp=4

Now structure is determined by following table.

lp+bp	Structure (Electron pair Geometry)
2	Linear
3	Trigonal planer
4	Tetrahedral
5	Triangular bipyrmidal
6	Square bipyramidal
7	Pentagonal bipyarnidal

VSEPR Theory

Determine the shape of following molecules.

NH₃

Central atom=N

l.p=1

b.p=3

l.p+b.p =4

Electron pair Geometry=Tetrahedral

Molecular Geometry= Pyramidal

H₂O

Central atom=O

l.p=2

b.p=2

l.p+b.p =4

Electron pair Geometry=Tetrahedral

Molecular Geometry=Bent/Angular

CCl₄

Central atom=c

l.p=0

b.p=4

l.p+b.p =4

Electron pair Geometry/Molecular Geometry =Tetrahedral

BeH₂

Central atom=Be

l.p=0

b.p=2

l.p+b.p =2

Electron pair Geometry /Molecular Geometry=Linear

BF₃

Central atom=B

l.p=0

b.p=3

l.p+b.p =3

Electron pair Geometry/Molecular geometry=Trigonal planer

PF₅

Central atom=P

l.p=O

b.p=5

l.p+b.p =5

Electron pair Geometry/Molecular geometry=Trigonal bipyramidal

SF₆

Central atom=S

l.p=0

b.p=6

l.p+b.p =6

Electron pair Geometry/Molecular geometry=Square bipyramidal

CH₄

Central atom=C

l.p=O

b.p=4

l.p+b.p =4

Electron pair Geometry/Molecular geometry=Tetrahedral

SF₄

Central atom=S

l.p=1

b.p=4

l.p+b.p =5

Electron pair Geometry=Trigonal bipyramidal

Molecular geometry=See-Saw

ClF₃

Central atom=Cl

l.p=2

b.p=3

l.p+b.p =5

Electron pair geometry=Trigonal bipyramidal

Molecular Geometry=T shape

XeF₄

Central atom=Xe

l.p=2

b.p=4

l.p+b.p =6

Structure=Square bipyramidal

Shape-Square Planar

Define Dipole moment.

The Product of the magnitude of charge and the distance between the centers of the two positive and negative and nonpolar covalent co charge is called dipole moment.

What is Debye(D)

Debye is unit of dipole moment.

What is polar covalent compound and nonpolar covalent compound?

Polar covalent Compound-Compounds having net dipole moment not equal to zero are polar covalent compound.

Non polar covalent Compound-Compounds having net dipole moment equal to zero are nonpolar covalent compound

Chose the polar and nonpolar compound in following compounds.

NF₃

Dipole moment of NF3 — Dipole moment of NF₃

H₂O

Dipole moment of H2O — Dipole moment of H₂O

BeF₂

Dipole moment of BeF2 — Dipole moment of BeF₂

BF₃

CH₄

Dipole moment of CH₄

NH₃

In NH₃ and NF₃ which has higher dipole moment?

Dipole moment of NH₃ is higher than that of NF₃. In NH₃ the orbital dipole due to lone pair is in same direction as the resultant dipole moment of N-H bonds ,whereas in NF₃ the orbital dipole is in the direction opposite to the resultant dipole moment of three N-F bonds.

Explain the term resonance in a covalent compound.

When a particular compound can be draw in more than two Lewis dot structure in which atomic positions are remain constant and differ on only arrangement of electrons.

Draw the resonating structure of following compounds.

CO₂

O₃

SO₃

NO₃^–

CO₃^2-

Define hybridisation.

The process of intermixing of the orbitals having slightly different energies and formation of new type of orbitals called hybrid orbitals of equivalent energies and shape.

What are the different types of hybridization and their structures.

Hybridisation	Structure
sp	Linear
Sp²	Triagonal planer
Sp³	Tetrahedreal
Sp³d	Triangular bipyramidal
Sp³d²	Square bipyramidal

Using hybridization theory show the formation of following molecules.

H₂O

Central atom is Oxygen

Electronic configuration in ground state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp³

Orientation of four sp³ hybrid orbitals in space

Overlapping between hybrid orbital and s orbital of hydrogen and formation of two bonds.

Hybridisation of H2O — Hybridisation of H₂O

BCl₃

Central atom is B

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp²

Orientation of three sp² hybrid orbitals in space

Overlapping between hybrid orbital and p orbital of Chlorine and formation of three bonds.

PCl₅

Central atom is P

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 3s ,3p and 3d orbitals

Orientation of five sp³d hybrid orbitals in space

Overlapping between hybrid orbital and p orbitals of chlorine and formation of five bonds.

Hybridisationn of PCl5 — Hybridisationn of PCl₅

SF₆

Central atom is S

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 3s ,3p and 3d orbitals

Orientation of five sp³d² hybrid orbitals in space

Overlapping between hybrid orbital and p orbitals of fluorine and formation of six bonds.

CH₄

Central atom is Carbon

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp³

Orientation of four sp³ hybrid orbitals in space

Overlapping between hybrid orbital and s orbitals of hydrogen and formation of four bonds.

NH₃

Central atom is N

Electronic configuration in ground state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp³

Orientation of four sp³ hybrid orbitals in space

Overlapping between hybrid orbital and s orbitals of hydrogen and formation of three bonds.

C₂H₄

Central atoms are two carbon atoms.

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp²

Orientation of three sp² hybrid orbitals in space

Similarly of other carbon atoms

Overlapping

Hybridisation of ethene

C₂H₂

Central atoms are two carbon atoms.

Electronic configuration in ground state

Electronic configuration in excited state

Hybridisation among 2s and 2p orbitals

Hybridisation is sp

Orientation of two sp hybrid orbitals in space

Similarly of other carbon atoms

Overlapping

What are the main features of molecular orbital theory?

(i)Like atoms are present in the atomic orbitals ,electrons in a molecule are present in a molecular orbitals.

(ii)The atomic orbitals of proper orientation combine to form molecular orbitals.

(iii)Like electron in a atomic orbitals are influenced by one nucleus ,in molecular orbital it is influenced by two or more nuclei.

(iv)The number of molecular orbitals formed are equal to the number of combining orbitals half are called bonding orbitals and another half are called antibonding orbitals.

(v)Bonding molecular orbitals have greater stability because they have lower energy than that of antibonding orbitals.

(vi)Molecualr orbitals are filled according to the aufbau principle,Pauli’s ,Hund’s rule.

What is LACO theory.?

LCAO-linear combination of atomic orbitals.

Let a molecule contain two atoms A and B .Formation of molecular orbitals are due to linear combination of atomic orbitals that can take place by addition and by subtraction of wave functions.

What is the sequence of energy levels of molecular orbitals.

Define bond order.

Bond order is defined as half of the difference between the number of electrons present in bonding and antibonding orbitals.

Explain stability of compound using bond order.

Stable molecule-N_b>N_a

Unstable molecule- N_b<N_a, N_b=N_a

When is compound diamagnetic and paramagnetic?

(i)If all the molecular orbitals in a molecule are doubly occupied the substance is diamagnetic and repelled by magnetic field.

(ii) If one or more molecular orbitals are singly occupied the substance is paramagnetic and attracted by magnetic field.

Discuss the bonding of H₂, He₂, Li₂, C₂, O₂ O₂⁺,O₂^– on MOT

Draw molecular orbital diagram of ,H₂,He_2,O₂.

H₂

He₂

O₂

Define H-bonding.

The attractive force which binds hydrogen atom of one molecule with the F,O,N of another molecule.

Define the two types of H-bonding.

(a)Intermolecular H-bonding.

(b)Intramolecular H-bonding.

(a)Intermolecular H-bonding.

It forms between two different molecules of the same or different compounds.

Example:H-F.H₂O etc

(b)Intramolecular H-bonding.

It forms when H-atom and F,O,N is present on the same molecule.

Example :O-nItrophenol.

Chemistry Notes Classification of elements and periodicity in properties

Classification of elements and periodicity in properties

Why do you need to classify elements?

It is very difficult to study chemistry of all elements individually ,because number of elements are very large.

Explain Dobereiner ‘s triads rule.

Dobereiner arranged three elements in increasing order of their atomic weight called triads ,He observed that the middle elements of each triads had an atomic weight equal to the arithmetic mean of the other two.

Example.Li(7) ,Na(23),K(39)

What was the major drawback of Dobereiner ‘s triads rule?

The triads rule valid for limited number of elements.

Explain Newlands Law of octaves.

He arranged the elements in increasing order of their atomic weights and noticed that every eight element have properties similar to the first element.

What was the major drawback of Newland’s octave rule?

The Law was true only for elements up to Ca.

Explain Mendeleev periodic law.

The properties of the elements are periodic function of their atomic weight.

What was the major drawback of Mendeleev periodic table?

Iodine with lower atomic weight than that of tellurium was placed in group VII along with F,Cl.Br.I.

Give special property of Mendeleev periodic table which makes it very special.

He proposed that some of the elements were still discovered and left the several gaps in the table. For example both Galium and Germaimum were unknown at the time Mendeleev published his periodic table. He left the gap under Al and Si and called these elements Eka Aluminium and Eka silicon.

What do you mean by Eka Aluminium and Eka silicon?

He left the gap under Al and Si and called these elements Eka Aluminium(Galium) and Eka silicon(Germanium).

What is modern periodic law?

The properties of the elements are periodic function of their atomic number.

What do you mean by periods and groups in long form of periodic table.

The Horizontal rows are called periods and vertical columns are called groups.

How many groups and periods are in long form of periodic table?

There are eighteen groups (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18) and seven periods (1,2,3,4,5,6,7)

What is the IUPAC name of elements having atomic number 101 and 102?

101-Unnilunbium.

102-unnilnium.

4f and 5f inner transition series of elements are placed in the separately in the periodic table why?

To maintain the structure and preserve the principle of classification by keeping elements with similar properties in a single column.

Why the elements of same group exhibit similar chemical behavior?

Because these elements have the same distribution of electrons in their outermost shell.

Long form of periodic table is classified into four blocks name that groups.

1.S-block elements.

2.p-block elements.

3.d-block elements.

4.f-block elements.

What is the general electronic configuration of the last shell of

1.S-block elements 2.p-block elements 3.d-block elements 4.f-block elements.

1.S-block elements-[ns^1-2]

2.p-block elements-[ns^1-2np^1-6]

3.d-block elements[(n-1)d^1-10ns^0-2]

4.f-block elements[(n-2)f^1-14(n-1)d^0-1ns²]

Define following terms.

1.Alkali metals.2.Alakaline earth metals.3.Representative elements or Main group elements.4.Noble gases.5.Halogens.6.Chalogens.7.Transition elements.8.inner transition elements.

1.Alkali metals.-Group 1 elements.

2.Alakaline earth metals. Group 2 metals.

3.Representative elements or Main group elements.-S-block elements and p-block elements.

4.Noble gases.Group 18 elements.

5.Halogens-Group 17 elements.

6.Chalogens-Group 16 elements.

7.Transition elements-d-block elements.

8.inner transition elements-f-block elements.

Why are group 1 elements called alkali metals?

When alkali metals are dissolved in water they form hydroxide which are basic in nature.

Why are group 2 elements called alkaline earth metals.

Hydroxide and oxide of group 2 elements are basic in nature and they are found in earth crust.

Group 18 elements are called Noble gases why?

All the orbitals in the valence shell of the Noble gases are completely filled by electrons and it is very difficult to remove electrons.

d-block elements are called Transition metals why?

d-block elements forma bridge between the chemically active metals of s-block elements and less reactive elements of group 13 and group 14.

What are Lanthanoids and Actinoids.

Lanthanoids-14 elements after La are called Lanthanoids.Last electron goes into 4f orbital.

Electronic configuration is 4f^1-145d^0-16s².

Actinoids. 14 elements after Ac are called Actinoids.Last electron goes into 5f orbital.

Electronic configuration is 5f^1-146d^0-17s².

What are transuranium elements?

The elements after Uranium are called transuranium elements.

Properties of s-block elements.

1.s-block elements are metals.

2.They are high reactive metals.

3.They have low ionization energy.

4.They lose the outermost electrons readily to form +1 ions(Group 1 elements)+and +2 ion (group2 elements.)

5.The compounds of the s-block elements are ionic except Li and Be.

Properties of the p-block elements.

1.p-block elements contain both metals and non metals.

2.Group 17 and group 16 elements are mainly nonmetals.

3.Group 17 and and Group 16 elements have very high negative electron gain enthalpy.

4.Group 18 elements are noble gases.

Properties of d-block elements.

1.They all are metals.

2.They form colored ions .

3.They have variable oxidation states.

4.They are paramagnetic.

5.They are good catalyst.

Zn,Hg,Cd do not show most of the properties of transition metals due to completely filled d –orbitals.

Properties of f-block elements.

1.They all are metals.

2.With in each series properties of the elements are quite similar.

3.The chemistry of actinoids are more complicated than the corresponding lanthanoids.

4.Actionoids are radioactive elements.

How many types of elements are in periodic table.

There are two types of elements.

1. Metals-78% of all elements are metals. They are located in left side of periodic table.

2. Non metals. They are located in at the top right side of the periodic table.

What are the properties of metals?

1.Metals are usually solid at room temperature.

2.They are good conductors.

3.They have high melting and boiling point.

4.They are malleable and ductile.

What are the properties of non metals?

1.Usually solids or gas at room temperature.

2.Low melting point and boiling point.

Boron and carbons are exceptions.

3.They are poor conductors of heat and electricity.

4.Brittle and are neither malleable and ductile.

5.Metallic character increases top to bottom and decreases left to right.

6.Non metallic decreases top to bottom and increases left to right.

What are semi metals and metalloids?

Elements which show properties of both metals and non metals.

eg. Silicon ,Germanium,Arsenic ,Antimony and Tellurium.

What do you mean by covalent radius and metallic radius.

Covalent radius-It gives the size of an atom of non metal. It is the half of the distance between two atoms when they are bound together by a single bond.

Metallic radius-Half of the distance between two adjacent kernels present at the lattice site in crystal.

Atomic size of elements increases top to bottom why?

As we go down the group number of shell per period increases thus size increases.

Atomic size of elements decreases from left to right in period why?

As we go from left to right in period shell number remains constant and electrons are added to same shell thus attraction between nucleus and outermost electron increases thus size decreases.

The size of anion is larger than its parent atom why?

It is due to addition of one or more electron would result in increased repulsion among the electrons and decrease in effective nuclear charge.

The size of cation is smaller than its parent atom why?

It is due to removal of one or more electron would result in decreased repulsion among the electrons and increases in effective nuclear charge.

The cation with the greater positive charge will have a smaller radius why?

It is due to greater attraction of the electron to the nucleus.

The anion with the greater –ve charge will have large radius why?

It is due to the net repulsion of the electron will more outweigh the nuclear charge and the will expand in size.

Define ionization enthalpy.

The energy required to the remove an electron from an isolated gaseous atom.

Define first Ionization enthalpy and second ionization enthalpy.

The first ionization enthalpy for an element X is the enthalpy change for the reaction.

The second ionization enthalpy for an elements X is the enthalpy change for the reaction.

Why Ionization enthalpies are always positive?

Because energy is always required to remove electron from an atom.

Why second ionization is always higher than the first ionization enthalpy.

It is more difficult to remove an electron from an positively charged ion than from neutral atom.

What is shielding effect or screening effect?

The effective nuclear charge experienced by an valance electron in an atom will be less than the actual charge on nucleus because of the repulsion between the core electrons and valance electrons.

Why 1^st ionization enthalpy of elements decreases top to bottom in group why?

It is due to atomic size increases top to bottom in group.

Ionization enthalpy of elements increases in period from left to right why?

Atomic size of elements decreases from left to right in period.

The first ionization enthalpy of boron(B) is slightly higher than Beryllium(Be) why?

In Be electron is removed from fully filled (stable) 2s orbital and in boron the electron is removed from partially filled(less stable) 2p orbital.

The 1^st ionization enthalpy of oxygen (o) is lower than that of Nitrogen(N) why?

It is easier to remove a electron from partially filled (2p⁴)orbital in case of oxygen than that of half orbital (2p³) orbital in case of nitrogen.

What are isoelectronic species?

Atoms and ions which contain the same number of electron is called isoelectronic dpecies.

e.g.O^2-=10 electron.F^–=10 electron.

Elctron gain enthalpy increases from left to right up to group 17 why?

It is due to the size of atom decreases from left to right in period.

Why negative electron gain enthalpy decreases from top to bottom in group why?

It is due to the size of atom increases from top to bottom in group.

Which oxidation state is shown by group 1 and group 2 elements?

Group 1 elements have only one valance electron hence they show +1 oxidation state Group 2 elements have two valance electron hence they show +2 oxidation state .

Periods 2 elements (top elements from group 13-17) show anomalous behavior why?

I t is due to small size ,high electronegativity and unavailability of d orbitals.

What do you mean by diagonal relationship?

Properties of 2 elements are similar with properties of period 3 elements diagonally.

The 1^st member of group 13-17 show anomalous behavior why?

1^stmember of group has only four valance orbitals one 2s and three 2p orbitals ,whereas the other members have d orbitals hence they can expand their covalency.

B can only form BF₄^– whereas Al Can form AlF₆^3- why?

It has due to B has only four valance orbitals but Al has d-orbitals thus it can expand its covalency.

The first member of p-block elements display greater ability to form multiple bonds to itself and to the other elements (like C=C,C=N,N=O) but other elements not why?

It is due to first member of p-block element has following properties.

1.Small size.

2.large charge/radius ratio.

3.High electronegativity.

Group 1 elements and halogens are highly reactive why?

Group1 elements have only one valance electron on their last shell hence they can lose electron easily and thus can form cation easily.

Halogens are seven electron on their last shell hence they need only on electron to complete their octet thus can form anion easily.

Chemistry Notes of Structure of Atom

Cathode ray discharge tube experiment/Discovery Of Electron.

When high voltage is applied to discharge tube at very low pressure ,current starts flowing through a stream of particles moving in the tube from –ve electrode(Cathode) to the +ve electrode(anode).These were called cathode rays particle latter these particles were called electrons.

What are the properties of cathode rays?

1.The cathode rays move towards anode from cathode.

2.They travel in straight line.

3.Deviations of cathode rays in electric field and magnetic field are similar to that the cathode rays consists of –vely charged particles.

4.Properties of cathode rays(such as e/m ratio) do not depend upon the materials of electrode and the nature of the gas present in the cathode ray tube.

How protons were discovered? What are canal rays?

Goldstein used a gas discharge tube which had a perforated cathode.When a high electrical potential is applied between the cathode and anode,”rays” are seen extending from the holes in the back of the cathode. These rays are beams of particles moving in a direction opposite to the cathode rays which are streams of electrons which move toward the anode. “channel rays” or “canal rays”, because they were produced by the holes or channels in the cathode. The lightest +ve ions, formed when there was some hydrogen gas in the tube .They were called protons.

What are the properties of anode rays?

1.Properties of anode rays (e/m ratio etc,) depend upon the gas present in the discharge tube.

2.Anode rays are +vely charged gaseous ions.

3.Properties of anode rays in electrical and magnetic field are opposite to the properties of cathode rays.

How neutrons were discovered?

Chadwick bombarded a thin sheet of Be by α-particles, new types were emitted.He named these particles neutrons.Neutrons have mass slightly greater than of protons and have no charge.

Thomson model of atom or plum pudding or watermelon model of atom.

1.Atom has spherical shape.

2.Positive charge is uniformly distributed throughout the atom.

3.The electrons are embedded into it in such a way which gives the most stable electrostatic arrangement.

4.Atom has no charge.

Explain Rutherford Model of atom.

The thin foil of gold was bombarded by α-particle, the following observations were made:

(i) Most of the fast moving α- particles passed straight through the gold foil.

(ii) Some of the α- particles were deflected by the foil by small angles.

(iii) Surprisingly one out of every 12000 particles appeared to rebound.

Rutherford concluded from the α particles scattering experiment that–

(i) Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected.

(ii) Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.

(iii) A very small fraction of α-particles were deflected by 180^o, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

On the basis of his experiment, Rutherford put forward the nuclear model of an atom, which had the following features:

(i) There is a positively charged center in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.

(ii) The electrons revolve around the nucleus in well-defined orbits.

(iii) The size of the nucleus is very small as compared to the size of the atom.

What is was the drawback of Rutherford atomic model of atom?

The orbital revolution of the electron is not expected to be stable. Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstable and hence matter would not exist in the form that we know. We know that atoms are quite stable.

Atomic number and Mass number.

ATOMIC NUMBER- The number of protons in the nucleus of an atom determines an element’s atomic number.

MASS NUMBER-Number of protons + number of neutrons is called mass number.

Define Isotopes and isobars with examples.

ISOBARS-Atoms with same mass number but different atomic numbers are called mass numbers.

Define electromagnetic waves or electromagnetic radiation.

When electrically charged particle move under acceleration, alternating electrical and magnetic fields are produced and transmitted in the form of waves called electromagnetic wave or electromagnetic radiation.

What are the properties of electromagnetic wave?

1.Oscillating electric and magnetic fields are perpendicular to each other and both are perpendicular to the direction of propagation of the wave.

2.They do not require medium and can move in vacuum.

3.There are many types of electromagnetic wave.

How is the frequency(٧) wavelength(λ), and the velocity(C) of light are related among each other?

Define wave number.

It is defined as the number of wavelength per unit length.

Arrange different types of electromagnetic waves in increasing order of their frequency.

What is black body? What is black body radiation?

The ideal body which emits and absorbs all frequencies is called black body and the radiation emitted by such a body is called black body radiation.

What is the relation between intensity and wavelength for a black body radiation.

At given temp ,intensity of radiation emitted increases with decreases of wavelength ,reaches at maximum value and the start decreasing with further decrease of wavelength.

Which properties of electromagnetic wave that is not explained by wave properties.

1.Black body radiation.

2. Photoelectric effect.

What is Planck’s quantum theory ?

1.The radiant energy which is emitted or absorbed by the black body is not continuous but discontinuous in the form of small discrete packets of energy, each such packet of energy is called a ‘quantum‘. In case of light, the quantum of energy is called a ‘photon‘.

2.The energy E of the quantum is related to the frequency .The quantity h, is Planck constant, is a universal constant with the value of 6.626 X 10^-34 Js.

What is photoelectric effect?

When certain metals (K.Rb.Cs etc) are exposed by a beam of light electrons are ejected from metals, the phenomena is called photoelectric effect.

Which observation of photoelectric effect explains the particle nature of light?

Ejection of electron depends on the frequency of light and it does not depend on the intensity of light.

Define Work function.

Minimum energy that can eject electron from metal surface.

Define threshold frequency

Minimum frequency below which photoelectric effect is not observed.

Give the relation between energy of photon, work function and kinetic energy during photoelectric effect.

On which factor no. of ejection of electrons depends.

The number of photoelectrons ejected is proportional to the intensity of incident radiation.

How can we say that electromagnetic radiations have dual behavior?

Interference and diffraction phenomena can explain by wave nature.

Photoelectric effect and blackbody radiation can explain by particle nature.

Define spectrum of white light

A ray of white light spread into series of bands called spectrum .Angle deviation is inversely proportional to the wavelength if the wave. Red color deviated the least while violet is deviated the most.

What is continuous spectrum?

A spectrum having no apparent gap or breaks throughout its entire spectrum.

Define emission spectra.

The emission spectra are produced by thin gases in which the atoms do not experience many collisions .The emission lines corresponds the photon of discrete energies that are emitted when excited atomic states in the gas back to the lower states.

Define absorption spectrum.

An absorption spectrum occurs when white light passes through a cold, dilute gas and atoms in the gas absorbs at characteristic frequencies, thus give rise to dark lines in the spectrum.

Define line spectra.

Atoms emit light only a specific wavelength with dark space between them called spectra.

Explain line spectrum of Hydrogen

When an electric discharge is passed through gaseous Hydrogen excited Hydrogen atoms produced emit electromagnetic radiation.

Types of different transition in spectrum of Hydrogen.

1.Lyman series-It involves transition which end with the ground state of Hydrogen(n=1)

2.Balmer series-It involves transition which end with shell n=2.

3.Paschon series-It involves transition which end with shell n=3

4.Brackett series-It involves transition which end with shell (n=4)

5..Pfund series-It involves transition which end with the shell (n=5)

The postulates of Bohr’s atomic model.

1.Electrons move around the nucleus in a circular path of fixed radius and energy fixed paths are called orbit.

2.The energy of an electron in the orbit does not change with time.

3.Energy is absorbed when electron move from a lower stationary to a higher stationary state to and energy is emitted when electrons move from higher stationary state to lower state.

4.The frequency of radiation absorb or emitted is equal to

5.Electrons can move only in those orbit for which its angular momentum is integral multiple of h/2π.

What are the advantages of Bohr’s Model.

1.The radii of the stationary are expressed as r_n=52.9 n²/Z pm

2.Energy of stationary state

En = -2.18×10^-18 Z²(1/n²) J.

Z=atomic number

3.Bohr’s theory can also be applied to the ions containing 1 electron example-He⁺.Li²⁺,Be³⁺

4..Velocity of electron moving in orbit can also be calculated.

Formula for calculating energy, frequency released or absorbed in line spectrum of Hydrogen.

What are the limitation of Bohr’s model?

1.It fails to account for the finer detail of the Hydrogen spectrum.

2.Unable to explain the spectrum of atoms other than Hydrogen atom.

3.This model is unable to explain the splitting of spectral lines in presence of magnetic field(Zeeman effect) or an electric field(stark effect).

4.Could not explain the ability of atoms to form molecule.

What is the reason for the failure of the Bohr’s model?

Bohr model of Hydrogen atom not only ignores dual behavior of matter but also contradicts Heisenberg uncertainty principle.

What is quantum mechanics?

The branch of science deals with the dual behavior of matter.

Write the Schrodinger wave equation for a system whose energy does not change with time.

H^{^}=Eψ where H^{^}is a mathematical operator called Hamiltonian operator.

What do you mean by ψ and ψ².

Schrodinger equation gives the possible energy levels the electron can occupy and corresponding wave function (ψ).The wave function ψ denotes an atomic orbital for an electron in an atom.Ψ² is probability density where finding an electron is maximum.

Plot a graph for orbital wave function ψ(r) and the variation of probability density ψ²(r) as a function of distance r of the electron from the nucleus for 1s and 2s orbital.

For 1s orbital the probability density is maximum at the nucleus and it decreases sharply as we move away from it.

For 2s orbital the probability density first decreases sharply to zero and again starts increasing after reaching a small maxima .it decreases again approaches zero as the value of r increases further.

Define nodal surfaces or nodal plane

The region where the probability function reduces to zero is called nodal surfaces.

Give the formula for for determining number of nodes for ns orbital and np orbital.

Ans. For ns orbital number of nodes =(n-1)

For np orbital number of nodes =(n-2)

Give the formula for determining the total number of nodes.

Total number of nodes =angular nodes + radial nodes

=l+(n-l-1)

=n-1

What do you mean by degenerate orbitals?

The orbitals having the same energy are called degenerate orbital.

Explain the de-Broglie theory.

According to de-Broglie theory matter like radiation has both particle and wave like properties.

λ=h/mv=h/P

m=mass of the particle.

V=velocity

P=momentum

Explain the limitations of de-Broglie theory.

de-Broglie theory is not applicable for ordinary objects due to short wavelength is associated with because of large mass of ordinary objects.The wavelengths associated with electrons and other subatomic particles can be detected experimentally.

What is Heisenberg Uncertainty principle.

It is impossible to determine simultaneously the exact momentum and exact position of electron.

What is the significance of Heisenberg uncertainty principle?

The effect of Heisenberg Uncertainty principle is significant only for motion of microscopic object and is negligible for macroscopic objects.

Let there is a ball have mass 10^-6 Kg.

What are Quantum numbers?

Each electron has a set of four quantum numbers called quantum numbers that specify it completely.

Describe the four quantum numbers.

1.Principal quantum numbers-The principal quantum number has the symbol ‘n’where n=1,2,3,4……..it tells which energy level an electron is in .Size and the energy of an orbit can also be determined after the finding the value of n.

2.Azimuthal quantum numbers or subsidiary quantum numbers-The Azimuthal quamtum number determines the orbital angular momentum of an atomic orbital and describes the shape of the orbital.

Value of l depends on n. l can have n value ranging from 0 to (n-1)

The various orbitals related to different values of l are sometimes called subshell.

l	symbol	Maximum electron	shape	Name
0	s	2	sphere	sharp
1	p	6	Two dumbells	principal
2	d	10	4 dumbells	diffuse
3	f	14	8 dumbells	fundamental

3.Magnetic quantum numbers(m)-It describe the orientation in space of a particular orbital.

Value of m depends on value of l. For any possible value of l the values of m are -l to +l

Total value of m= 2l+1

Subshell	l	m	Possible orientation
s	0	0	Only one way in which a sphere can be oriented in a space
p	1	-1,0,+1	P_x, p_y, p_z
d	2	-2,-1,0,1,2	dxy,dyz,dzx,dx²,dy²,dz²

4.Spin quantum number.

An electron spin around its own axis. The two orientation can be describe by spin quantum number and take the values of +1/2 and -1/2.

Draw the shape of s orbital.

Draw the shape of p orbitals.

Draw the shape of d orbitals.

What do you mean by valance electron and core electron?

Valence electron-The electrons present in the last shell of atom are called valence electrons.

Core electron-The electron present in completely filled shells are called core electrons.

What is Aufbau principle?

I.Electrons are filled in a orbital in order of their increasing energies.

II.The lower the value (n+l )the lower will be energy of that orbital.

III.If the two orbitals having same (n+l ) the lower the value of n the lower will be energy of that orbitals.

Thus 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<4f<5d<6p<7s.

What is Pauli exclusion principle?

No two electrons in an atom can have the same set of four quantum numbers.

Which quantum number differentiate the behavior of two electrons?

Two electrons have the same value of n,l,m but must have the opposite spin quantum numbers.

Which rule explain that the maximum number of electrons in the shell with quantum number n is equal to 2n² ?

Pauli exclusion principle

Explain Hund’s rule

The pairing of electrons in the orbitals belonging to same subshell does not take place until each orbital belonging to that subshell has got one electron.

Write the electronic configuration of Cr.and Cu.

₂₄Cr-1s²2s2²p⁶3s²3p⁶4s¹3d⁵.

₂₉Cu-1s²2s2²p⁶3s²3p⁶4s¹3d¹⁰.

Why Cr and Cu adopt d⁵ and d¹⁰ electronic configuration?

Because half filled and fully filled orbitals are more stable.

Important Question and Answers

1.What is atoms in chemistry?

Chemistry Notes Some Basic Concept Of Chemistry

Dalton’s atomic theory.
I.Matters are made up of invisible atoms.
II.When atoms of different elements combine with each other they form compound.
III.Atoms of same element have identical properties.
IV.Chemical reaction involve reorganization of atoms .These are neither created nor destroyed in chemical reaction.

What do you mean by precision and accuracy of quantity?
Precision refers to the closeness of various measurements for the same quantity.Accuracy is the agreement of particular value to the true value of results.

Explain the term scientific notation.
Exponential notation in which any number can be represented in the form of N x 10ⁿ where n is an
exponent having +ve or –ve value and N is equal to 1-10.Example-scientific notation of 232.508 is 2.32508 X10^2.

What is significant figure of a number.
Significant figures are meaningful digits which are known with certainty.
Rule 1.All non zeros digits are significant.
Example
325 m has 3 significant figures.
.2584 has 4 significant figures.
Rule 2. Zeros preceding to first non zeros digits are not significant.
Example
.05 m has 1 significant figure.
.0063 has 2 significant figures.
.2584 has 4 significant figures.
Rule 3.Zeros between two non Zeros digits are significant.
Example: 3.008 has 4 significant figures.
Rule 4. Zeros at the end or right of a number are significant provided they are on the right side of decimal point.
Example: .3000 has 4 significant figures.
Rule 5.Terminal Zeros are not significant if there is no decimal point.
Example : 200 has 1 significant figure.
Example 300.0 has 4 significant figures.
Rule 6.Counting number of objects have infinite significant figures.
Example 2 pens have infinite significant figures.

Explain the law of conservation of mass.
According to Lavoisier matter can neither be created nor be destroyed.
Explain the law of definite proportion.
A given compound always contains exactly the same proportion of elements by weight.

Explain the law of multiple proportions.
If two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole number.

Example: 𝐻₂ + 1/2𝑂₂→ 𝐻₂𝑂
2𝑔 16𝑔 18𝑔
𝐻₂ + 𝑂₂ → 𝐻₂𝑂₂
2𝑔 32𝑔 34𝑔
Fixed mass of Hydrogen (2g) combine with the 16 g and 32g of oxygen which is a simple ratio(16:32 or 1:2).

What is Gay Lussac’s law of gaseous volume?
Gases combined or produced in a chemical reaction in simple ratio at same temperature and pressure.
What is Avogadro’s Law?
Equal volume of gases at the same temperature and pressure contain equal no. of molecules.
Define one mole.
One mole is the amount of a substance that contain as many as entities as there are in 12g of carbon
_¹²𝐂 isotope.1 mole of any substance =6.023 x 10²³ particles.

What is molar mass?
The mass of one mole of a substance in gram is called its molar mass.
Example=Molar mass of water =18g.
What is mole concept?
(i) When atomic mass is expressed in gram, it gives mass of one mole of that element.
Example: Mass of one mole of sodium atoms =23 gram.
(ii) When molecular mass is expressed into gram it gives mass of one mole of that compound.
Example: Mass of one mole of water (H₂O) =18 gram.
(ii) When molecular mass is expressed into u/amu it gives mass of one molecule of that compound.
Example: Mass of one molecule of water (H₂O) =18 u.
(iv) When atomic mass is expressed into umu it gives mass of one atom of that element.
Example: Mass of one atom of sodium atom =23 u
(v) Volume of one mole of gas at STP=22.4 liter.
Define amu/u.
One atomic mass unit is defined as a mass exactly equal to one-twelfth of the mass of one carbon atom. 1amu =1.66 x 10^-24 g.
What is average atomic mass?
Many naturally occurring elements exist as more than one isotopes. Hence average atomic mass is
calculated.

Define Molecular mass.
Molecular mass is the sum of atomic masses of the elements present in a molecule.
What is formula mass?
Some substance do not exist as a single entity, for these substances instead of molecular mass formula mass is calculated, it denote ratio of two atoms in a given sample of compound.
What do you mean by % composition?
Percentage of particular element in a particular compound is called %composition of that element.

What is empirical formula and molecular formula?
An empirical formula represents the simplest whole number ratio of various atoms present in a compound whereas the molecular formula show the exact number of different atoms present in a molecule.

Explain Stoichiometry concept.

Consider following reaction.
𝐶𝐻₄(𝑔) + 2O₂(𝑔) → 𝐶O₂(𝑔) + 2𝐻₂O(𝑔)
The following stoichiometry concepts are.

1.One mole of CH₄ reacts with two moles of O₂ gas to give one mole of CO₂ and two moles of 𝐻₂O(𝑔

2. One molecule of CH₄ reacts with two molecules of O₂ to give one molecule of CO₂ and two molecules of H₂O.

3. 22.4 of CH₄ (g) reacts with 44.8 L of O₂ (g)as to give 22.4 L of CO₂ (g) and 44.8 L of H₂O(g)

4.16g of CH₄ reacts with 64g of O₂ to give 44g of CO₂ and 36 g of H₂O.
What is limiting reagent?
The reactant which gets consumed, limits the amount of product formed and is, therefore called the limiting reagent;
Explain the following concentration terms.
a.Mole fraction
b.Mass %
C.Molarity.
d.Molality.

1.Mole fraction:

The ratio of number of moles of a particular component to the total number of moles of solution is called mole fraction of that component.

let ‘A’ dissolves in substance ‘B’ and their number of moles of 𝑛𝐴 and 𝑛𝐵
respectively, then the mole fraction of A and B are given as-
Mole fraction of A= 𝑛𝐴 ⁄ (𝑛𝐴 + 𝑛𝐵)
Mole fraction of B= 𝑛𝐵 ⁄ (𝑛𝐴 + 𝑛𝐵)

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Important Question and Answers

Chemistry Notes Some Basic Concept Of Chemistry