chapter -1 fundamental of chemistry

8/3/2019 Chapter -1 Fundamental of Chemistry

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Chapter -1 Fundamental of

Chemistry There are three fundamental particles

posses in an atom named Electron,

Proton and Neutron respectively.


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Electron It was discovered by J.J. Thomson.

It is a negatively charged particle.

Its mass is 9.108x10-31 kg.


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Proton It is a positively charged particle.

Its mass is 1.672.10-19kg.


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Neutron It was discovered by Chadwick.

It is neutrally charged particle.

Its mass is equal to proton.


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Atomic Nucleus The central part of an atom which

consists proton and neutron is called as

Atomic Nucleus.


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Atomic Number The number of planetary electrons in an

atom is called as Atomic Number.


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Mass Number The sum of the number of Protons and

Neutron is called as Mass number.


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Bohrs Atomic Model Electrons in an atom revolve round the nucleus in circular

orbits.

The circular orbits are stationary and having constantenergy.

Emission or absorption of energy by electron will be inquanta. While doing so electron jumps from one orbit toother.

The energy emitted or absorbed will be equal to thedifference in energies of the two orbits.

The angular momentum of the electron revolving in astationary orbit is equal to integral multiples of h/2.

mvr =nh/2


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Limitations of Bohrs Atomic

Model Bohrs theory could not explain the atomic

spectra of higher elements such asHe,Li,Be,B,Cwhich have more than one

electron. Bohrs theory did not provide any

explanation for union of atoms to formmolecules.

Bohrs theory could not explain the ZeemanEffect. Bohrs model could not justify the

quantization of angular momentum.


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Quantum Numbers Quantum numbers are used for knowing the

position, energy, angular momentum, shape,

etc of an atom. There are four types of Quantum Numbers: -

Principle Quantum Number (n)

Azimuthal Quantum Number (l) Magnetic Quantum Number (m)

Spin Quantum Number (s)


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Principal Quantum Number(n) Principal quantum number gives thew

size and energy of the orbit and

indicates the main energy level. It hasvalues 1,2,3,4,.and are also indicatedby K,L,M,N


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Azimuthal Quantum Number() Azimuthal quantum number indicates

the number of possible sub-levels in

each energy level. can take valuesfrom O to (n-1)a total n values where

n is the principal quantum number.

Values of =(0,1,2,3) aredonated by s,p,d,f.


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Magnetic Quantum

Number(m) m determines the orientation of

orbits in space. It also gives the

number of orbitals in each sub level.The permitted values are dependingupon the l. For a given value of the

values of magnetic quantum numberare given by - or + including O.


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Spin Quantum Number(s) Spin quantum number(s) is due to

spinning of e- . The e- spin may be

either in the clockwise () oranticlockwise direction ().


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Paulis Exclusion Principle No two electrons of the dame atoms

can have the same values for all the

quantum numbers.


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Aufbau Principle

According to Aufbaus principle e- tendto occupy orbitals of minimum energy

and the orbitals with lower energy arefilled first before filling of orbitalshaving higher energy starts.


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Hunds rule

Pairing of e- takes place when all theavailable degenerate orbitals are

occupied by one e- each.


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Orbit

Orbit is a circular path followed byrevolving e- around the nucleus.

The distance of the orbit from thenucleus for a given e- is fixed.

Orbit has 2D representation.

Orbits are circular in shape.


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Orbital

Orbital is a region of space around thenucleus of the atom where an e- is most

likely to be found. It is impossible to know the exact position of

an e- in an orbital of an atom.

Orbital has 3D representation.

Orbital have different shapes like sphere,dumb-bell etc.


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Modern Periodic Table

The modern periodic table consists ofhorizontal rows called periods and

vertical columns called groups.


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Periods

There are 7 periods. First three are calledshort period. The fourth and fifth period iscalled long periods. The sixth period is calledvery long period. The seventh period isincomplete.

General characteristics of periods: -

Same number of shells of electrons. Period ends with inert gas.

Gradual change in property.

Change in valency.


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Groups

There are 9 groups from 0 to VIII group. The0 group contains inert gases. In the longperiods, the group I to VII are further sub-divided into A and B families.

General characteristics of groups: -

Valences are same.

Similarity in properties. Gradual Change in properties in some

elements.


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Chemical Bonding

When two atoms tend to remaintogether than separate from each

other, they are said to be in chemicalbonding with each other.


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Electronic Theory of Valency

According to electronic theory ofvalency, the valency of an element

depends on the number of electronpresent in the outermost orbit of theatom of the element known as valance

electron.


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Types of Bonds

Ionic Bond

Covalent Bond

Co-Ordinate Covalent Bond

Metallic Bond


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Ionic Bond

Ionic bonds are made by the transfer of theelectron from one atom to another.

Example: - The atomic number of Sodium (Na) is11. So its electronic configuration is 1s2 2s2 2p63s1. Also the atomic number Chlorine (Cl) is 17.So its electronic configuration is 1s2 2s2 2p6 3s23p5.

The Na atom loses one electron to the Cl atom.In doing so Na atom acquires a unit positivecharge while Cl atom acquires a unit of negativecharge. These two oppositely charged atomsattracts each other and forms an Ionic Bond as

NaCl.


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Ionic Compound

Ionic compounds are made by thetransfer of the electron from one atom

to another. They conduct electricity in a fused

state.

They show isomerism. They are usually liquids o gases in room

temperature.


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Covalent Bond

Covalent bonds are made by mutualsharing of electrons.

Example: - Oxygen atom has 6electrons in its outer most orbit. In theformation of Oxygen 2 atoms of Oxygen

contributes one electron each forsharing and thus acquire a stableconfiguration as O2.


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Covalent Compound

Covalent compounds are made bymutual sharing of electrons.

They doesnt conduct electricity.

They dont show isomerism.

They are usually solids.

chapter -1 fundamental of chemistry

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