Chemical Bonding Chapter 4 Section 1

A chemical bond is: a force of attraction between any two atoms in a compound. Bonding between atoms occurs because it creates a more stable arrangement for the atoms.

Lewis Symbols – Dot Diagrams Convenient way to show the valence electrons

Three types of bonding Metallic bonding – results from the attraction between metal atoms and the surrounding sea of electrons Ionic bonding – results from the electrical attraction between large numbers of cations and anions Covalent bonding – results from the sharing of electron pairs between two atoms

Ionic Bonding Many atoms transfer electrons and other atoms accept electrons, creating cations (positive metal ions) and anions (negative nonmetal ions). The resulting ions are attracted to each other by electrostatic force.

Ionic bonding between Na and Cl

Covalent bonding In many cases electrons do not completely transfer from one atom to another. The electrons between atoms are shared.

Covalent bonding between H 2 Hydrogen’s electron configuration is 1s 1 Because both H atoms need 1 more electron to become isoelectronic with He, it is unlikely that either will give up an electron. They share the two electrons. H· + H ·  H : H

Types of Covalent Bonds When electrons are shared equally the bond is called a NONPOLAR covalent bond. (i.e. H 2 ) Sometimes the electrons between two atoms are NOT shared equally. The bond created is called a POLAR covalent bond..... H· + ·Cl:  H:Cl:....

How to classify bond types Electronegativity – measure of the ability of an atom to attract electrons in a chemical bond Each element on the periodic table is assigned an electronegativity value (see page 87) that ranges from 0.7 to 4.0. The difference in the electronegativity determines the bonding type (ionic, polar covalent, or nonpolar covalent).

If the electronegativity difference is: 1.7 and higherionic 0.3 to 1.7polar covalent 0.0 to 0.3nonpolar covalent

Practice Problems What type of bond will occur between iodine and the following elements: cesium, iron, and sulfur? The electronegativities of each are: Iodine2.5 Cesium0.7 Iron1.8 Sulfur2.5

Answers to problems Bonding between I and: Electronegativity difference Bond Type Cesium2.5 – 0.7 = 1.8Ionic Iron2.5 – 1.8 = 0.7Polar covalent Sulfur2.5 – 2.5 = 0.0Nonpolar covalent

What if I get an electronegativity difference that is 0.3 or 1.7? These cut-off numbers are guidelines. It is a gradual change not stair-step.

Determine the type of bond between the following pairs. Bonding between Electronegativity difference Bond type Li & Cl S & O Ca & Br P & H Si & Cl S & Br

Answers Bonding between Electronegativity difference Bond type Li & Cl3.0 – 1.0 = 2.0Ionic S & O3.5 – 2.5 = 1.0Polar covalent Ca & Br2.8 – 1.0 = 1.8Ionic P & H2.1 – 2.1 = 0.0Nonpolar covalent Si & Cl3.0 – 1.8 = 1.2Polar covalent S & Br2.8 – 2.5 = 0.3Nonpolar covalent