Chemical Bonding and Molecular Shapes

Mr. McIsaac

Carleton North High School

Chemistry 112Chapter 8

Electron Arrangement(Energy Levels, Sublevels, Orbitals)

• Electrons travel around the nucleus at certain distances, called energy levels.

• Inside each energy level, there are sublevels; the number of sublevels is equal the number of the energy level:– 1st energy level has 1 sublevel (s)– 2nd energy level has 2 sublevels (s, p)– 3rd energy level has 3 sublevels (s, p, d)– 4th energy level has 4 sublevels (s, p, d, f)– 5th energy level has 5 sublevels (s, p, d, f, g)

Electron Arrangement (cont.)

• Inside each sublevel, there are orbitals –specific regions/areas inside the e cloud where individual e’s exist.

• An orbital may be empty, or may hold 1 or 2 e’s. Any orbital can hold a maximum of 2 e’s.

• An outer level (valence level) can hold a maximum of 8 e’s. So, an outer level has a maximum of 4 orbitals.

Electron Arrangement (cont.)

• Stated another way, an outer level has a maximum of 2 sublevels (s, p).

• An s sublevel has 1 orbital; a p sublevel has 3 orbitals. Total = 4 orbitals = 8 e’s (2 per orbital).

• Valence electrons exist in these outer 4 orbitals.

Filling The Outer Level• As bonded elements:

– The first 4 e’s (1, 2, 3, 4) will singly/separately occupy each of the outer 4 orbitals – the 1st in the s orbital, and 2nd, 3rd, 4th in each of the 3 p orbitals.

– The next 4 e’s (5, 6, 7, 8) will pair up in each of the outer orbitals – the s, and then the 3 p orbitals.

• As unbonded elements (FYI; we don’t worry about it):– The first 2 e’s (1 and 2) will fill the s orbital– The next 3 e’s (3, 4, 5) will singly/separately occupy

each of the 3 p orbitals.– The next 3 e’s (6, 7, 8) will pair up in each of the 3 p

orbitals.

Lewis Electron Dot Diagrams• In a Lewis Electron Dot Diagram for an

element, the symbol of the element represents the nucleus and all the inner electrons, and the 4 sides around the symbol represents the 4 valence orbitals.

• Each of the above dot diagrams is equivalent – any of the 4 sides is the same

Lewis Electron Dot Diagrams

• Electrons like to exist in pairs, and single e’s bond/share with single e’s from other atoms.

• When two atoms share a pair of e’s, it is called a bonded pair, shared pair, or covalent bond.

• Notice that when showing dot diagrams for different elements forming a compound, it is common to use dots for one element and x’s for the other – it just makes it easier to follow.

VSEPR TheoryAnd Predicting Molecular Shapes

• Valence Shell Electron Pair Repulsion (VSEPR) theory is the understanding that pairs of e’s will repel each other and move as far apart from each other as possible.

• Predicting molecular shapes and bond angles can be done by drawing dot diagrams showing the pairs of e’s (shared and unshared) around a central atom.

5 Molecular ShapesFrom

Single Bonds

Double and Triple Bonds

• Adjacent atoms can share more than one pair of electrons.

• Try O2, N2, CH2O, CHP

Summary: Predicting Molecular Shapes

• Draw the Lewis Dot Diagram for the molecule to determine the number of bonding and non-bonding electron pairs.

• Make sure all atoms are present.• Cannot have any single e’s (dots/x’s) left.• Only adjacent atoms can bond.• E’s/dots from same atom cannot pair up.• When determining the shape of a

molecule with multiple bonds, treat the multiple bonds as if they were single bonds (i.e. one bonding side or direction)