Chemical Bonds

What We Already Know

Valence electrons are important because…

They are the electrons in the outermost shell

They are the same for each element in a group (column).

Want to follow the octet rule of having 8 electrons in the outer shell.

They are the electrons that are involved in bonding.

Octet Rule

How many electrons would carbon want?gain 4

How many electrons would nitrogen want?gain 3

How many electrons would oxygen want?gain 2

Something New…Lewis Structures

show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule

How do we write them?1. Write the symbol of the element.2. Find its number of valence electrons3. Starting at the right, draw a dot to represent each of the

valence electrons and continue counter clockwise until you have used them all up.

4. Each side of the element can only have two dots, because each orbital can only hold 2 electrons

5. Lone electrons tell you how many bonds will form

Example: Carbon

Write the symbol for the element, carbon

It is in group 4 so it has how many valence electrons?

Starting at the right, put one dot on each side until you run out of electrons

Count the number of lone electrons to know how many bonds will form

C

More Examples:

Mg

B

O

Ar

How many bonds will each element form?

Chemical Bonds

An attractive force between atoms or ions that binds them

together

Two types of bonds:Ionic bond: bond formed between two ions by the transfer of electronsCovalent bond: bond formed by sharing electrons

Properties of Ionic Bonds

When a metal (+) and a non-metal (-) combine

Oppositely charged ions attract

Soluble in water

Conducts electricity when dissolved

Covalent Bond

Found to the right of the staircase

Between two non-metals of similar electronegativity

Electronegativity – the ability of an atom of an element to attract electrons when the atom is in a compound

Do all atoms share electrons equally?

The sharing of electrons can be looked at as a sort of tug-of-war between the nucleus’ of the two atoms

involvedIf that’s the case then who wins?

-nonpolar covalent bond – when the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally

-polar covalent bond (polar bond) - a covalent bond between atoms in which the electrons are shared unequally.

The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

How do we determine the bond polartiy?

Difference in electronegativity determines bond type

Above 1.7 = ionic 0.3 – 1.7 = polar covalent 0-0.3 = non-polar covalent

Look at periodic table in CRM p.13

Find the difference between the two numbers

Which is the more polar covalent?(larger # = more polar)

O-O or O-H

Another type of bond….(as if we don’t have enough to remember)

ReviewIonic- Metal with nonmetal

Covalent – Nonmetal with nonmetal

What about two metals?

Metals do not combine with metals. They form alloys, which is a solution of a metal in a metal

Examples: steel, brass, and bronze

However

Atoms of metal are still held together with…

Metallic Bond

Metallic bond – bond found in metal; holds metal atoms together very strongly

Formed between atoms of metallic elements

Good conductors at all states, lustrous, very high melting points