Chemical bonding Covalent Bonding

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!

Structure of Covalent Substances Covalent substances may exist as: simple molecular structures giant covalent structures Diamond Graphite Silicon dioxide

‘Allotropes’: Different (structural) forms of the same element Diamond One of the allotropes of carbon Diamond is one form of the element carbon. ‘Allotropes’: Different (structural) forms of the same element ‘Isotopes’: Atoms of the same element with the same number of protons but different number of neutrons

These four carbon atoms form a tetrahedron. Diamond Has a giant covalent structure Giant network of carbon atoms held together by covalent bonds in a tetrahedral arrangement These four carbon atoms form a tetrahedron.

Diamond Each carbon is joined to four other carbon atoms by strong covalent bonds. Each carbon has four covalent bonds.

Properties of Diamond Very high M.P. and B.P. (Diamond melts at about 3500°C) Hardest natural substance Reason: Carbon atoms are held together in a giant rigid structure by strong covalent bonds. A lot of energy is required to break these strong covalent bonds.

Properties of Diamond Does not conduct electricity Insoluble in water All electrons are held in the covalent bonds. No ions or free electrons to conduct electricity Insoluble in water

Uses of Diamond Used in cutting other hard solids (because of its hardness) E.g. Diamond-tipped drills to cut through rock

Graphite Another form of the element carbon Another allotrope of carbon Has a giant covalent structure Consists of layers of carbon atoms (flat two-dimensional layers)

Graphite Within the layer Each carbon atom is joined to three other carbon atoms by strong covalent bonds. Arranged in rings of six atoms

Arrangement of carbon atoms in one layer Structure of Graphite Arrangement of layers Arrangement of carbon atoms in one layer Strong covalent bond Strong covalent bond Weak force between layers

Properties of Graphite Very high M.P. and B.P. (Within each layer) The bonds between the carbon atoms are difficult to break – strong covalent bonds Soft and slippery Weak forces between the layers  the layers can slide past each other Strong covalent bond Weak force between layers

Properties of Graphite The only non-metal that conducts electricity Reason: Each carbon atom has one valence electron that is not used in bonding. Free to move  Able to conduct electricity

Uses of Graphite Pencil lead: Made of graphite and clay Since it is soft, it flakes off and stick to paper when we write. Lubricant (for hot machines) It does not decompose at high temperatures.

Silicon Dioxide a.k.a. silica Found in nature as sand or quartz Consists of silicon and oxygen atoms Has a giant covalent structure like diamond SiO2 tells us the ratio of silicon atoms to oxygen atoms is 1:2

Physical Properties of Giant Covalent Substances Physical state At room temperature, all substances with a giant covalent structure are solids. Strong covalent bonds make it hard. M.P. and B.P. High M.P. and B.P. because of its strong covalent bonds

Physical Properties of Giant Covalent Substances Solubility in water Insoluble in water Electrical conductivity Do not conduct electricity (except graphite!) Diamond Graphite

Chemistry Insights TB Practice Questions Chapter 6 (P.110-113) MARCH HOLIDAYS HW