What? Why? When? Which? Where? How? Mod.H U.3 L3&4 Chemical Bonding What? Why? When? Which? Where? How? Mod.H U.3 L3&4

3 Types of Bonding Ionic Bonding Covalent Bonding Metallic Bonding

Bonding is… the transfer or sharing of electrons concerned with the Valence Electrons

Ionic Bonding Ionic bonding is an electrical attraction between two oppositely charged atoms.

When.. Lose an electron - Atom is Positive Positive Ion is called Cation ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… Gain an electron - Atom is Negative Negative Ion is called Anion

Characteristics of Ionic Compounds 1) Crystalline solid at room temp. 2) Have higher melting and boiling points compared to covalent compounds. 3)Conduct electrical current in solution state. 4)Extremely polar (charged) bonds. 5)Most are soluble in water.

Magic # The magic number is 8 Every atom wants to gain electrons up to 8, or lose electrons to equal zero, In order to be stable. Exception= Hydrogen= only needs two electrons

Lewis Dot Structure 1) Write the Atomic Symbol 2)Count up the number of valence electrons. 3)Draw a dot around the symbol for each valence electron.

Helpful Hint An easy way to check if a bond is Ionic: One atom must be from group 1, 2, or 13 on the periodic table and the other atom from groups 15-17.

Oxidation Number (Charge) Group 1 2 13 14 15 16 17 18 Charge +1 +2 +3 -4 -3 -2 -1

Covalent Bonds Covalent Bonds are formed as a result of the sharing of one or more pairs of valence electrons. Each atom donates half of the electrons to be shared.

2 forms of covalent bonds 1) Polar Covalent - unequal sharing of electrons 2) Non-Polar Covalent – equal sharing of electrons between atoms.

Is held together by

Single Covalent Bond A single covalent bond would be the sharing of two electrons between the 2 bonded atoms. H-H H-Cl F-F The dash line is symbolic of the bonding pair. One line equals 2 electrons

Covalent Bonding in Chlorine

Compare:

Double Covalent Bond A double covalent bond is 2 pairs of electrons being shared. O=O C=O

Triple Covalent Bond A triple covalent bond is the sharing of 3 pairs of electrons. N=N C=C C=N

Covalent bonds form molecules A molecule is a neutral group of atoms held together by covalent bonds Examples: water molecules, oxygen molecules…..

WATER MOLECULE

Written as H2O H:O:H O Single bonds H H

DRAW THESE AMMONIA: NH3 Chlorine gas: Cl2 Methane: CH4

Methane CH4

NH3 H : N : H H

Properties of covalent bonds: Low melting point, boiling point Brittle

Shared pair of electrons Cl : Cl

Metallic Bond The metallic bond occurs only between metal atoms. In this type of bond the valence electrons overlap and are free to move about The electron clouds of all metals participating in the bond. It is similar to a “Sea of Electrons”.

A Sea of Electrons

Metallic bonds: A ‘sea’ of shared electrons

Electrons can move freely Metallic bonds account for the properties of metal Conductivity, ductility, malleability, higher temps Example: paper clips!