Unit 1.5

• Ionic solids are giant lattices of positive and negative ions. The ions are arranged in such a way that the electrostatic attraction between the oppositely charged ions is greater thatn the electrostatic repulsion between ions of the same charge.
• Sodium chloride has a 1:1 ratio in its ionic solid structure. Each ion is surrounded by 6 ions of the opposite charge. The coordination number of each ion is 6
• Casium chloride has a 1:1 ratio in its ionic solid structure. Each ion is surrounded by 8 ions of the opposite charge. The coordination number is 8.
• Casium chloride has a larger coordination number than sodium chloride because caesium is larger than sodium and so more chloride ions can fit around it.
• Ionic solids have high melting amd boiling points, due to the strong electrostatic forces between oppositely charged ions. It takes a large amount of energy to overcome these forces of attraction.
• Ionic solids are often soluble in water. Water molecules are polar, and will be attracted to positive and negative ions.
• Ionic solids are hard but brittle. When force is applied, layers of ions slide over each other, causing ions of the same charge to be next to each other. The ions repel each other and the structure shatters.
• Giant covalent structures consist of networks of covalently bonded atoms that stretch throughout the entire structure. They are sometimes referred to as macromolecules.
• Diamond has a giant covalent structure, with each carbon covalently bonded to 4 others in a tetrahedral shape. This structure has a very high melting point due to the energy required to break the strong covalent bonds. Diamonds are very hard, due to the strength of the covalent bonds and the geometric shape of the structure. They are insoluble in water as there are no ions to attract polar water molecules, and they are poor conductors of electricity due to having no delocalised electrons or ions to carry the charge
• Graphite is a giant covalent structure made up of carbons. Each carbon is covalently bonded to three others, forming hexagonal rings. The 4th electron from each carbon is delocalised within the layer, and layers are held togther by weak temporary dipoles.
• Graphite has a very high melting point due to the strong covalent bonds in the hexagonal layers. It is insoluble in water, as there are no ions to attract the polar water molecules. They are good conductors of electricity due to the delocalised electrons.
• Simple molecular solids have covalent bonds within molecules held togther by weak intermolecular forces.
• Simple molecular structured have low melting and boiling points due to the weak intermolecular forces holding the molecules togther. They are soft, as the weak forces between the molecules are easily broken. They are normally insoluble in water, as there are no ions to attract the polar water molecules, however certain compounds which can form hydrogen bonds will be able to dissolve in water. They are poor conductors of electricity, as they do not contain delocalised electrons.
• Iodine and ice have simple molecular structure.
• Iodine atoms are covalently bonded in pairs, which are held togther by weak temporary dipoles in a regular pattern
• Ice is arranged in rings of 6 water molecules held togther by hydrogen bonds.
• When metal atoms come close to one another, each atom loses control of its outer electrons and become cations. These electrons are delocalised, and are free to move throughout the metal. Metal atoms are not ionised as the electrons are still within the structure and are not lost.
• Metals have high melting temperatures due to the strong forces of attraction between the metal cations and delocalised electrons. They are hard, as metallic bonding is very strong. They are insoluble in water, as there are no ions. They are good conductors due to the delocalised electrons and they are malleable and ductile. When a force is applied to a metal, the layers can slide over each other, however the delocalised electrons prevent forces of repulsion being formed between the layers.
• Metal structures are hard, as metallic bonding is very strong. They are insoluble in water, as there are no ions.
• Metals are good conductors in a solid and molten state due to the delocalised electrons.
• Metals are malleable and ductile. When a force is applied to a metal, the layers can slide over each other, however the delocalised electrons prevent forces of repulsion being formed between the layers.
• Simple molecular structured have low melting and boiling points due to the weak intermolecular forces holding the molecules togther.
• Simple molecular structures are soft, as the weak forces between the molecules are easily broken.
• Simple molecular structures are normally insoluble in water, as there are no ions to attract the polar water molecules, however certain compounds which can form hydrogen bonds will be able to dissolve in water.
• Simple molecular structures are poor conductors of electricity, as they do not contain delocalised electrons.