Covalent Bonding Covalent Bonding A covalent bond is

Covalent Bonding

Covalent Bonding A covalent bond is when valence electrons are shared between two atoms with high electronegativity (nonmetals). A molecule is a neutral group of atoms held together by covalent bonds. A molecular or covalent compound is a compound made up of nonmetals that are covalently bonded.

Covalent Bonds (cont) Two atoms held together by sharing a pair of electrons are joined by a single covalent bond so that both atoms have a full valence shell like a noble gas!

Covalent Bonds (cont) Single bond: One shared pair of electrons Double bond: Two shared pairs Triple bond: Three shared pairs Double and triple bonds form when an atom needs to share additional electron pairs to become like a noble gas Triple bonds are the strongest and the shortest http: //www. tutorvista. com/content/chemistryi/chemical-bonding/covalent-bond-animation. php

Formulas Molecular compounds can have their formula written out two different ways: molecular and structural Molecular formulas are chemical formulas for molecules and show what atoms make up a molecule and how many of each there are. Ex: CO 2 one carbon two oxygens Structural formulas show the atoms are bonded and are done using Lewis structures.

Strategy for drawing Lewis Structures: Step #1 Look up valence number for each atom and add them up Carbon dioxide (CO 2) C 4 (Group 4) O 6 (Group 6) x 2 = 12 4 + 12 = 16 Total Valence Electrons

Step #2 Determine how many valence electrons each atom needs to have for a complete outer energy level (Follow the octet rule). 8 for most atoms 2 for hydrogen 6 for boron CO 2 Carbon needs a total of 8 valence electrons to follow the octet rule Each oxygen atom also needs 8 valence electrons (2 x 8 = 16) Total valence electrons needed is 8 + 16 = 24

Step #3 Subtract the number of valence electrons in step 1 from the number of valence electrons needed in step 2. This determines the number of bonding electrons. Step 2 (Valence electrons needed): 24 Step 1 (Valence electrons present): -16 Bonding electrons = 8

Step #4 Divide the number of bonding electrons from step 3 by 2. This gives you the number of bonds needed. Bonding electrons from step 3 = 8 8 divided by 2 = 4 bonds needed

Step #5 Draw an arrangement of the atoms for the molecule that contains the number of bonds you found on step 4. The atom with the lowest electronegativity goes in the center. Carbon always goes in the center Hydrogen never goes in the center Remember the HONC rule Hydrogen and the halogens make 1 bond Oxygen and group 6 make 2 bonds Nitrogen and group 5 make 3 bonds Carbon and group 4 make 4 bonds O C O

Step 6 Find the number of lone pair (nonbonding) electrons by subtracting the number of bonding electrons from step 3 from the valence electrons in step 1. Arrange these electrons, in pairs, until all the atoms satisfy the octet rule. Number of valence electrons from step 1 = 16 Number of bonding electrons from step 3 = -8 Nonbonding electrons to be placed = 8 O C O

Lewis Structures Draw Lewis structures for the following: H 2 O PH 3 CCl 2 H 2 C 2 H 4 OH NO 2 NH 4+

Naming Covalent Compounds Use prefixes to determine how many of each type of atom If first prefix is mono, leave it off The last element listed ends in -ide Number Prefix 1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona- 10 Deca-

Naming Covalent Compounds (cont) Name the following CO Si. O 2 N 2 O P 2 O 4 SI 2 Cl. F CCl 2 H 2 C 2 H 4

Naming Covalent Compounds (cont) Write the formulas for the following: Octacarbon octahydride Diphosphorous trinitride Carbon disulfide Bromine monofluoride

A word on one more type of bonding… Metallic bonding: Metallic bonding happens in metals. In metallic bonding the nuclei of the atoms sit in a “sea” of electrons that can move freely between the nuclei. Metal properties, such as malleability, ductility, shininess, and conductivity are a result of metallic bonding and the ability of the electrons to move freely. Alloys are mixtures of metals. Brass is an alloy of copper and zinc Stainless steel is an alloy of iron, chromium, and zinc