Chemical Bonding

What holds things together?

Bonding

• Involves the valence electrons or outermost electrons

• Outermost electrons in the last energy shell

How many valence electrons does N have?

Group 5A – 5 valence electrons

Bonding…

• Lewis dot structures show the valence electrons around at atom and for most molecules and compounds a complete octet for the elements

N Al

Write out the electron configuration for the following atoms and ions:

He

Ne

Ar

Kr

Na Cl

NaCl

+ -

electron transfer

and the formation of ions

This is the formation of an ionic bondionic bond.

ClCl

Cl2 This is the formation of a covalent bondcovalent bond.

sharing of a pair of electrons

and the formation of molecules

Ionic Bond

• Between atoms of metals and nonmetals with very different electronegativity

• Bond formed by transfer of electrons• Produce charged ions all states.

Conductors and have high melting point.

• Examples; NaCl, CaCl2, K2O

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BONDbond formed by the sharing of

electrons

Covalent Bond

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electron pairs• Stable non-ionizing particles, they

are not conductors at any state

• Examples; O2, CO2, C2H6, H2O, SiC

Chlorine atom 2,8,7

2 Chlorine atoms

Outer shells only

Chlorine molecule Cl2

Molecules have no overall electric charge

Molecular or covalent compounds are usually gases or liquids – they have low melting points and low boiling points

Forces between molecules very weakForces (bonds) between atoms in the molecule very strong

Each outer shell has 8 electronsElectrons shared

Covalent Bonds:

Water H2O

Methane CH4

Ammonia NH3

Hydrogen H2

Hydrogen Chloride HCl

Oxygen O2

N.B. Oxygen has a double bond

Oxygen

O168

Oxygen atom 2,6

2 Oxygen atoms (outer shells only)

Double covalent bond

O O

More sharing examples

O2

N2

O O

N N

O O O O

N N N N N N

double bond (2 pairs)

triple bond (3 pairs)

Share until octet is complete.

octet complete

NH3

NH

H

H

normal covalent bond

(each atom supplies an electron)

Some more sharing examples

ionic covalent

valence electrons

Comparison of Bonding Types

sharing of electrons

transfer of electrons

ions moleculesconductive non-

conductive