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