Chemical Bonding

Types of Bonds There are two kinds of Chemical bonds Ionic and covalent An ionic bond is formed when electrons are transferred from one atom to the other e.g. NaCl A covalent bond is formed when electrons are shared between atoms e.g. H 2 0

Octet Rule The noble gases are very unreactive. They form practically no compounds. Why? They have 8 electrons in their outer shell- unreactive Rule: when bonding occurs, atoms tend to reach an electron arrangement with 8 electrons in their outer shell

This fills the outer shell and tends to give the atom the stability of the inert gasses. The Octet Rule Atoms tend to gain, lose, or share electrons until they have eight electrons. 8

Ionic bonding An ion is a charged atom or group of atoms An ionic bond is the force of attraction between positively charged ions in a compound e.g. NaCl Na + =Sodium ion = loses an electron Cl¯ = Chlorine ion = gains an electron Na = 2,8,1Na + = 2,8 Cl = 2,8,7Cl¯ = 2,8,8 Loses one electron Gains one electron

NaCl e¯e¯ N=2 N=1 e¯e¯ N=2 N=1 e¯e¯ N=2 N=1 e¯e¯ N=2 N=1 Na 2,8,1 Cl 2,8,7 Na+ 2,8,Cl¯ 2,8,8 N=3 Na Na + Cl Cl¯

MgO e¯e¯ N=2 N=1 N=3 e¯e¯ N=2 N=1 N=3 Mg= 2,8,2O= 2,8,6 e¯e¯ N=2 N=1 N=3 Mg 2+ = 2,8, e¯e¯ N=2 N=1 N=3 O 2¯ = 2,8,8 O O2¯O2¯ Mg Mg 2+ e¯e¯ e¯e¯ e¯e¯ e¯e¯

Extra Slides Another casualty in the War of the Atoms.

Properties of Ionic Compounds Ionic compounds are usually solid at room temperature Usually have high melting and boiling points Usually dissolve in water Usually conduct electricity when molten and when dissolved in water

Spherical atoms packed closely together. Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 70

Molecule A molecule is a group of atoms joined together e.g. H 2 H 2 0 is a molecule consisting of two hydrogen atoms and one oxygen atom

Covalent Bonding Covalent bonds are formed as a result of the sharing of one or more pairs of bonding electrons. Each atom donates half of the electrons to be shared e.g. H 2

H atom H 2 molecule Shared electrons Hydrogen molecule H H H H

The oxygen molecule Oxygen 2,6 e¯e¯ e¯e¯ e¯e¯ e¯e¯ e¯e¯ Double bond N=2 N=1 N=2 N=1 N=2 N=1 Oxygen O 2 OO O O

Oxygen gas molecules Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 68

Oxygen 2,6 Two hydrogen atoms Water H 2 0 e¯e¯ e¯e¯ e¯e¯ e¯e¯ e¯e¯ e¯e¯ The water molecule N=2 N=1 N=2 N=1 O H H O HH Covalent bond

Carbon 2,44 Hydrogen atoms Methane gas CH 4 Methane N=2 N=1 N=2 N=1 C HH HH H H H HC Covalent bond

Properties of Covalent Compounds Covalent compounds are usually either a liquid or gas at room temperature Usually have low melting and boiling points Many (but not all) do not dissolve in water Covalent compounds do not conduct electricity

Covalent Bonding n = 1 O n = O2O2 Sharing of electrons to achieve a stable octet (8 electrons in outer shell) O

Formation of Cation 11p + sodium atom Na e-e- loss of one outer electron e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- sodium ion Na + 11p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

Formation of Anion 17p + chlorine atom Cl e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- gain of one outer electron chloride ion Cl 1- 17p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

Formation of Ionic Bond chloride ion Cl 1- sodium ion Na + 11p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- 17p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e-

Ionic Bonding n = 2 Na [Ne]3s 1 n = Cl [Ne]3s 2 3p 5 Na + [Ne] Cl - [Ne]3s 2 3p 6 NaCl Transfer of electrons to achieve a stable octet (8 electrons in outside shell).

To investigate the ability of ionic and covalent substances to conduct electricity Apparatus required: power supply or battery, bulb, leads, crocodile clips, carbon electrodes Chemicals required: water, copper sulphate solution, methylated spirits, sodium chloride solution, table sugar solution, paraffin oil

Method Set up apparatus as shown Insert the carbon electrodes into a solution of copper sulphate Write down what you observe Repeat the experiment with various other solutions. Using a wash bottle, wash the carbon electrodes before putting them into the next solution

Results Summarise the results as follows: Name of substance Conduct electricity (Yes/No) Copper sulphate Methylated spirits Sodium chloride Paraffin oil Table sugar