Leaving Certificate Chemistry 5 – Covalent Bonding Leaving Certificate Chemistry

Objectives for today To learn what a covalent bond is To draw what happens in bonds using Bohr diagrams and dot and cross diagrams

Covalent Bonding

Formation of Chlorine (Cl2) Formed from 2 chlorine sharing a pair of electrons with each chlorine contributing 1 electron to the covalent bond Outer Shell Cl Cl Cl Cl One Shared Pair of Electrons = A single bond

N N N N O H H O H H Dot & Cross Diagrams X X X X X X X For a Nitrogen Molecule (N2) X N N N N X X X X For a Water Molecule (H2O) O H H O X X H H

Double Covalent Bonds For ethene (C2H4)

Triple Covalent Bonds For ethyne (C2H2)

Learning objectives Today you should learn about.. What a polar covalent bond is Two examples of a polar compounds The dissolving rule

Investigating the characteristics of covalent compounds Test Circle the correct characteristic Try to break the substance It is brittle/ it is soft and squashy/ it is very strong Try to dissolve the substance in water It is soluble in water / it is not soluble in water Try to heat the substance – what happens It has low melting and boiling points/ it has high melting and boiling points Try to pass electricity through the substance It does not conduct electricity/ it does conduct electricity when molten or in solution

The Characteristics of Covalent Compounds They have low melting points and low boiling points They do not conduct electricity They are usually insoluble in water 10

Melting and boiling point: molecules Simple molecular substances have low melting and boiling points because the molecules together are not held tightly together. weak bonds between molecules strong bonds within molecules

Conductivity – covalent substances Substances with covalent bonding do not conduct electricity because there are free electrons to carry a charge through a solution electrons unable to move and carry a charge

Polar Covalent Bonds

H F Polar Covalent Bonds X Hydrogen Fluoride is an example of a polar covalent molecule δ - δ+ H F X

O H H Polar Covalent Bonds X X Water is another example of a polar covalent molecule δ 2- O X X δ+ H H δ+

Testing if a liquid is polar If a liquid is polar covalent then it will be deflected towards a charged rod. Try out this test with some liquids and see which are polar!!!

Demonstration The Polarity Test for Liquids Charged Rod Non polar – hexane, cyclohexane Charged Rod A polar covalent compound will deflect towards a charged rod

Polar Substances in Everyday Life Alcohol (Ethanol) Water

Non-Polar Substances in Everyday Life Toluene (Methylbenzene) is a common industrial solvent Acetone in nail varnish remover

Investigating which dissolves which Name of substance Is it ionic, polar covalent or pure covalent Name of solvent Is it pure covalent or polar covalent/ Did it dissolve? Sodium chloride ionic Water Polar covalent Toluene Pure covalent Iodine Pure covelent

Solubility of different substances In general …Like Dissolves Like Ionic substances and polar covalent substances will dissolve in polar covalent solvents. Pure Covalent substances will dissolve in nonpolar solvents water, cyclohexane, ethanol, and glycerol. Candle wax