Bellwork Tuesday Draw the Lewis Structure and name the correct shaped molecule for all of the following. BF3 CH4 HBr NH3

8.4 Polar Bonds and Molecules In covalent bonds, the sharing of electrons can be equal or it can be unequal.

Nonpolar Covalent Bonds Nonpolar covalent bond - This is a covalent bond in which the electrons are shared equally. EXAMPLES: H2 Br2 O2 N2 Cl2 I2 F2 Br Cl H N F I O O Br Cl H N F I

Polar Bonds and Molecules If the sharing is unequal, the bond is referred to as a dipole. A dipole has 2 separated, equal but opposite charges. “∂” means partial _ +

Polar Bonds and Molecules Polar covalent bond - a covalent bond that has a dipole It usually occurs when 2 different elements form a covalent bond. EXAMPLE: H + Cl  H Cl

Polar Bonds and Molecules Electronegativity - This is the measure of the attraction an atom has for a shared pair of electrons in a bond. Electronegativity values increase across a period and up a group.

Electronegativity Electronegativity values can be used to determine the degree of electron sharing which demonstrates the type of bond that will occur. Difference > 2  Ionic Difference 0.1 - 1.9  Polar Covalent Difference = 0 Nonpolar

The difference in electronegativity is:

Examples: Identify the type of bond for each of the following compounds: HBr Br = 2.8 H = 2.1 0.7 .1 < < 1.9 Polar Covalent H Br

Examples: N N NaF F = 4.0 Na = 0.9 3.1 N2 N = 3.0 N = 3.0 0.0 Na F > 2 Ionic Non-Polar Covalent N N

Molecular Polarity If there is only one bond in the molecule, the bond type and polarity will be the same. If the molecule consists of more than 2 atoms, you must consider the shape. To determine its polarity, consider the following: Lone pairs on central atom If so… it is polar Spatial arrangement of atoms Do bonds cancel each other out (symmetrical)? If so… nonpolar Do all bonds around the central element have the same difference of electronegativity?

Attractions Between Molecules Van der Waals forces – the weakest of the intermolecular forces. These include London dispersion and dipole-dipole forces. London dispersion forces – between nonpolar molecules and is caused by movement of electrons

Attractions Between Molecules van der Waals forces(cont.)- Dipole interactions – between polar molecules and is caused by a difference in electronegativity.

Attractions Between Molecules Hydrogen bonds – attractive forces in which hydrogen, covalently bonded to a very electronegative atom (N, O, or F) is also weakly bonded to an unshared (lone) pair of electrons on another electronegative atom. O O H H H H O H H

Attractions Between Molecules Ionic Bonding-occurs between metals and nonmetals when electron are transferred from one atom to another. These bonds are very strong.

Summary of the Strengths of Attractive Forces Ionic bonds hydrogen bonds dipole-dipole attractions LDF

Bellwork Wednesday Write the correct attractive force: ionic bond, LDF, dipole-dipole, or hydrogen bond. CO2 CF4 NH3 H2O NaCl

Quick Review before Thursday Quiz Name and write the formula for a compound containing sodium and nitrogen. Draw Lewis Dot Structure then give the shape, polar/nonpolar, and the attractive force for each of the following: BH3 PH3 CS2 CH4

Bellwork Friday Draw the lewis diagram, name and write the formula for a compound containing calcium and phosphorous. Draw Lewis Dot Structure then give the shape, polar/nonpolar, and the attractive force for each of the following: SF6 SBr5- XeCl2

Vocab Unit 11 page 56 Electronegativity Intermolecular Forces Molecular Type Bond Type Valence Non Polar Covalent Polar Covalent Crystal lattice Metallic Bond