Chemical Bonding and Molecular Shapes Mr. McIsaac Carleton North High School Chemistry 112 Chapter 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: –1 st energy level has 1 sublevel (s) –2 nd energy level has 2 sublevels (s, p) –3 rd energy level has 3 sublevels (s, p, d) –4 th energy level has 4 sublevels (s, p, d, f) –5 th 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 1 st in the s orbital, and 2 nd, 3 rd, 4 th 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 Theory And 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 Shapes From Single Bonds

Double and Triple Bonds Adjacent atoms can share more than one pair of electrons. Try O 2, N 2, CH 2 O, 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)