Chemical Bonding Covalent Bonding

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Some queries.. Physical Properties of Ionic compounds Solubility How it happens? Electrical conductivity Why do ionic compounds only conduct electricity in the molten or aqueous state?

Bonding and structure explains the properties of a substance! Overview Bonding Ionic Covalent Metallic Structure Giant ionic Simple molecular Giant covalent Giant Metallic Example Sodium chloride Water Diamond Iron Bonding and structure explains the properties of a substance!

Compare and Contrast

Ionic VS Covalent Ionic Bond Covalent Bond Similarities Differences Octet Rule: Electronic configuration of a noble gas (PS: Everybody wants to be noble!!) Differences Ionic Bond Covalent Bond Between positive ions of metals and negative ions of non-metals Between non-metal atoms Electrons are transferred Electrons are shared

What to do??

Covalent Bonding

Covalent Bond: The Definition A covalent bond is… a bond formed by the sharing of a pair of electrons.

More about COVALENT BONDING Each atom acquires a stable octet structure Electronic configuration of noble gas (Full shell) = Energetically stable Formed between atoms of non-metals (but there are exceptions!) “Spectrum” of bonds

Covalent Compounds of ELEMENTS Hydrogen, H2 (Single covalent bond)

Covalent Compounds of ELEMENTS Chlorine, Cl2 (Single covalent bond)

Covalent Compounds of ELEMENTS Oxygen, O2 (Double covalent bond)

Covalent Compounds of ELEMENTS Nitrogen, N2 (Triple covalent bond)

Covalent Compounds of COMPOUNDS Draw the ‘dot-and-cross’ diagram for each of the following covalent compounds. Hydrogen chloride Ammonia

Covalent Compounds of COMPOUNDS Water, H2O

Covalent Compounds of COMPOUNDS Carbon dioxide, CO2

Simple Molecular Substances Consists of small molecules, e.g. bromine

Simple Molecular Substances Within the molecule Atoms are held together by strong covalent bonds Between molecules Weak van der Waals’ forces (intermolecular forces)

Iodine, I2 Within each iodine molecule, the iodine atoms are held together by strong covalent bonds. Between the iodine molecules, there are only weak van der Waals’ forces holding the molecules together.

Methane, CH4 In a molecule of methane, CH4, the four C–H covalent bonds are strong. However, weak van der Waals’ forces between methane molecules hold them together loosely. Therefore, methane exists as a gas at room temperature and pressure.

Physical Properties Physical state Low M.P. & B.P. Most substances are liquids or gases at room temperature. Forces between molecules are weak, allowing molecules to move freely. Low M.P. & B.P. Little energy required to overcome the (weak) intermolecular forces (Usually <200°C)

Melting & Boiling Points Covalent substance Melting point (C) Boiling point (C) Carbon dioxide -56 -79 Chlorine -101 -35 Hydrogen -259 -253 Methane -183 -161 Oxygen -214 Water 100

Physical Properties Volatility Electrical conductivity Solubility Low B.P. = Volatile Evaporate easily (to give a smell) Electrical conductivity Do not conduct electricity. (Some exceptions, e.g. graphite) No free-moving ions or electrons to conduct electricity Solubility Most molecular substances are insoluble in water, but dissolve in organic solvents. (Some exceptions, e.g. alcohol and sugar, hydrogen chloride)

So, what have you learnt? Covalent bonding The definition of a covalent bond A covalent bond is a bond formed by the sharing of a pair of electrons. Formed between atoms of non-metals (with exceptions!) Atoms share electrons so that a octet structure can be obtained

Steps to take… Ionic or covalent? Determine the electronic configuration of the atoms involved How many electrons needed to achieve stable electronic structure? Now, transfer/share the electrons!

So, what have you learnt? Simple molecular structure Small covalent molecules Strong covalent bonds between the atoms in the molecule Weak intermolecular forces 5 physical properties

Giant Covalent Structures Diamond Graphite

Giant Covalent Structures Diamond Each carbon atom is joined to four other carbon atoms by strong covalent bonds. (Draw!) Graphite Each carbon atom is joined to three other carbon atoms by strong covalent bonds. (Draw!)