Chemical Bonding

How do atoms combine to form compounds?What holds them together?

Octet Rule

States that atom tend to acquire the electron configuration of a rare gas

How many valence electron are there in the rare gases?

What is a full set of valence electron?

Lewis Electron dot Structure

By Gilbert Lewis Consist of a chemical symbol of an element

surrounded by a number of dots. The chemical symbol represents the nucleus of the atom. The dots represents the valence electrons

Ex: 1A 2A 3A 4A 5A

H. . . . .

Li. . Be. .B. . C. .N.

. .

Types of bonds

Ionic bonds

Metallic bonds

Covalent bonds

Bond A force that holds the atoms

together

Metallic Bond

Is the electrical attraction between the valence electron and the positive nuclei.

Properties

Do not dissolve in water Conduct electricity Lustrous, malleable, ductile, and hard solids Made entirely of metals atoms

Valence electrons are free to move throughout the substance, like a sea of electrons

Ionic Bonds

Formed by the transfer of electrons from one atom to another to achieve stability

Usually formed between Groups 1,2,3 and 6 or 7

Example : NaCl, MgCl2 Na+ Cl - ------> NaCl

Mg 2+ Cl- ------> MgCl2

Ionic Structure of Sodium Chloride

Na+ and Cl- ions alternate each other

Properties of Ionic Compounds

High melting and boiling point Compounds in the solid state are non

conductors of electricity but in the molten or liquid state and in aqueous solution, are conductors of electricity

Brittleness

Brittleness is a typical property of ionic compounds

Covalent Bonding

Formed by the sharing of electrons between atoms

Usually formed between H and elements in group 4,5,6,and 7

Are represented by dashes between atoms Single bond(-), double bond(=) and triple bond( )

Example: Show the covalent bond formation of H2, O2 and NH3

H. .H H-H

.. .. .. ..

: O . . O: : O=O: . .

.. .. ..

.N. . H H. . N. .H H-N-H . :

H H

Types of Covalent Bonding

Polar Covalent

Nonpolar Covalent Bond

Polar Covalent Bond

formed when combining atoms differ in electronegativities

Electronegativity

the ability of an atom to draw electrons toward itself

Trend: Left to right increases

top to bottom decreases

Ex: H Cl +

Ex: C O

+

Nonpolar Covalent Bond

Formed by equal sharing of electrons between nonmetallic atoms of the same kind resulting in zero differences in their electronegativities

Ex: H2, F2

Predicting type of Bond using Electronegativity Difference

Electronegativity Values of Some elements Li Be B C N O F

1.0 1.5 2.0 2.5 3.0 3.5 4.0

Na Mg Al Si P S Cl

0.9 1.2 1.5 1.8 2.1 2.5 3.0

K Ca Ga Ge As Se Br

0.8 1.0 1.6 1.8 2.0 2.4 2.8

Ex: Predict the type of bond form between the following elements a) etween the following pairs of element C and Cl 2.5 – 3 = .5 polar F and F 4 – 4 = 0 non polar Mg and O 1.2 - 3.0 = 1.8 ionic

Writing Lewis Structures for Covalent Compounds

Steps Add up the total valence valence electron The atom with the highest covalency ( # of covalent bonds form by the

atom) is considered as the central atom Bond the other atoms to the central atom by a single bond. Distribute the remaining valence electron to the attached atoms first then to

the central atom last Check if the octet rule is followed by each atom If there is deficiency in the octet rule, form a multiple bond

Ex: CO2 total valence e = 4 + (6x2) = 16 . .. .C. O: . ..Covalency number = 4 2 :O=C=O: .. ..

H

Li Be

Na Mg

K Ca

Rb Sr

Cs Ba

Fr Ra

A C N O F

Al Si P S Cl

Ga Ge As Se Br

In Sn Sb Se I

Tl Pb Bi Po At

He

Ne

Ar

Kr

Xe

Rn