Atomic Structure & Chemical Bonding:Structure of the atoms:

Atoms are made up of 3 basic particles:

(i). Protons,

(ii). Neutrons,

(iii). Electrons.

Properties of the particles are shown on the table below:

Particles Relative Mass

Relative charge

Protons Concealed in the Nucleus

+1

Neutrons Concealed in the Nucleus 0

Electrons Round the nucleus in orbits(in shells)

1/1840

Proton Number:

Number of protons in the nucleus of an atom.

This is also known as Atomic Number. Number of protons and Electrons are equal in an NEUTRAL ATOM.

Nucleon Number:

Sum of protons and neutron numbers. It is also known as MASS NUMBER.

aXb

where,

a= proton number,

b= nucleon number,

X= element symbol.

*the form mentioned above is the pattern used for writing elements in the Periodic Table.

Electronic Configuration:

Distribution of elements around the nucleus in various orbitals/ shells.

Number of electrons in a particular orbit are determined by the formula: 2n2 Where, n= number of orbit.

11Na23: 11 electrons

13Al27 : 13 electrons

Valency number of an element is equal to the number of electrons gained or lost by that element to attain the Noble Gas Configuration.

Isotopes:

Different atoms of same element with same number of protons and electrons But different number of neutrons.

e.g.

(i). 17Cl35 = Protons= 17,

Neutrons= 18

(ii). 17Cl37 = Protons= 17,

Neutrons= 20

Ions Formation:

Atoms other than the Group 0 of the Periodic table are generally unstable in nature due to the lack of a stable octit or duplet structure.

Atoms will lose electrons to form +ive ions and gain electrons to form –ive ions eith a stable octet or a stable duplet.

e.g.

11Na23 =

But

Na+1=

And so on….every metal will show the same behavior with increasing number of lost electrons with increasing group and vice versa for NON-METALS.

Ionic Bonds:

Formation Conditions:

Always formed between a metal and a non-metal. It is formed by the complete transfer of electrons

form metals to non-metals. It is formed by the electrostatic forces of

attraction between oppositely charged ions.E.g.NaCl:

Important Points About Ionic Bonding:

Ionic compounds exist in the form of giant ionic lattice (joined by strong electrostatic forces) and

throughout the lattice, there are strong electrostatic forces of attraction between oppositely charged ions which are very hard to break, therefore, ionic compounds have high Melting and Boiling Points.

Strength of ionic bond depends upon two factors: (i). charge of ions: Higher the charge, stronger the ionic bond, higher the melting point & vice versa. e.g.if we compare MgO & Na2O, MgO has stronger ionic bonding and higher Melting Point due to the high charge og Mg+2 as compared to Na+.

(ii). Ionic Size/ Ionic Radius: Higher the ionic size, weaker the ionic bonding, lower the M.P & vice versa. e.g. if we compare NaCl and NaF, NaCl has weaker ionic bond and lower M.P. due to the large ionic radius/size of Cl- as compared to F-.

Characteristics of Ionic Compounds:1. Ionic compounds have high melting and boiling

points.2. Ionic compounds exist in form of solid state.3. Most of the ionic compounds are soluble in H2O.4. Ionic compounds do not conduct electricity in

sloid state but are good conductors of electricity in molten state as well as in the form

of their aqueous solution. Due to the availability of free/ mobile ions.

Covalent Bonding: A covalent bond is formed between two non-

metals. It is formed by the mutual sharing of electrons and

in sharing, both the atoms contribute equal number of electrons. Sharing is done to attain the noble gas configuration.e.g.

CO2:

Types of Covalent Compounds: There are 2 types:

(i).Simple Molecules: These are the covalent compounds in which one molecule is held with another molecule through weak intermolecular forces of attraction which are easy to break, therefore, such compounds have low M.P & B.P. e.g. H2O, NH3, Ch4, HCl, Cl2, Br2, F2, H2, F2, O2, CO2 etc.

Strength of intermolecular forces of attraction depends upon the size of the molecule. Bigger the size, sttonger the forces and vice versa.

(ii).Macromolecules/ Giant Covalent Molecules: These are the covalent compounds which exist in theform of giant covalent lattice and throughout the lattice, there is strong covalent bonding which is very hard to break, therefore, such compounds have very high M.P. & B.P. e.g. Diamond, Graphite , Silica etc.

Characteristics of Covalent compounds; Low M.P & B.p(except macromolecules). Covalent compounds do not conduct

electricity. Covalent compounds are insoluble in HY2O

but dissolve in most of the organic solvents. Covalent compounds exist in all the 3

physical states.

DiAMOND:

Structure:

Diamond exists in the form of giant covalent lattice and throughout the lattice, there is covalent bonding in which each carbon atom is bonded with four other carbon atoms in a Tetrahydral Way.

Characteristics:

Diamond has a very high M.P. Poor conductor of Electricity. Hardest known natural substance. It has a high density.

Uses:

Used in jwellery. Used to cut glass and drills rocks. Also used as abrasive material.

*Allotropes:

Different crystalline of same element which have similar chemical properties but different physical properties are known as Allotropes & this phenomena as known Allotrope.

Graphite:

Structure:

Graphite has a layer type structure in which each carbon atom is bonded to 3 other carbon atoms in a hexagonal arrangement to form rings of regular hexa bonds. The different layers are held with each other through weak Wander Vaals Forces of attraction.

Properties:

Graphite has very high M.P. and B.P. Good conductors of electricity due to the availability

of electrons between the layers. It is very soft because layers can slide over each

other due to weak Wander Vaals forces(causing friction).

Uses:

Used as lubricant(due to being slippery). Used as a conductor(as an electrode during

electrolysis).

Silicon: Silicon has a giant molecular structure similar to diamond. In silicon, each silicon atom is covalently bonded with 4 silicon atoms in a tetrahydral way.

Properties:

It has a high M.P. It is a non-conductor of electricity due to the non-

availability of mobile/delocalized electrons. It is very hard but less than diamond.

Silica(SiO2):

Structure Of Silicon Bonds

Silicon has a giant covalent lattice in which each silicon atom is covalently bonded with 4 oxygen atoms and each oxygen atom is covalently bonded with 2 silicon atoms.

Properties:

It is very hard but less than diamond. It has very high M.P. It is poor conductor of electricity.

Metallic Bonding:Metals are highly electropositive(ability to lose electrons) so they give away their valence electrons resulting in the formation of positively charged metal ions. These positively charged metal ions are embedded in a sea of delocalized electrons and are held with each other through these delocalized electrons.

Al has strongest metallic bonding and highest M.P.

2. Ionic Radius:Smaller the ionic radius, stronger the metallic bonding, higher the M.P and vice versa.

E.g.: If we compare Li, Na and K, Li has the highest M.P and strongest metallic bonding due to its smaller ionic radius.

Properties Of Metals:1. Metals have high M.P and B.P because of strong

forces of attraction between the sea of negatively charged electrons and positively charged metal ions.

2. Good conductors of electricity in the solid state as well as in the molten state due to availability of delocalized/mobile electrons.