Foundations of Chemistry. Philippa B. Cranwell

Foundations of Chemistry - Philippa B. Cranwell


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Water, H2O Schematic illustration of the dot and cross diagram of water. Schematic illustration of the display formula of water. Ammonia, NH3 Schematic illustration of the dot and cross diagram of Ammonia. Schematic illustration of the display formula of ammonia. Methane, CH4 Schematic illustration of the dot and cross diagram of Methane. Schematic illustration of the display formula of methane. Ethene, C2H4 Schematic illustration of the dot and cross diagram of Ethene. Schematic illustration of the display formula of ethene. Ethyne, C2H2 Schematic illustration of the dot and cross diagram of Ethyne. Schematic illustration of the display formula of ethyne. Oxygen, O2 Schematic illustration of the dot and cross diagram of oxygen. Schematic illustration of the display formula of oxygen. Nitrogen, N2 Schematic illustration of the dot and cross diagram of nitrogen. Schematic illustration of the display formula of nitrogen.

      To ensure that you understand this topic, try to draw each of the molecules in Table 2.1 using dot‐and‐cross diagrams and starting from the component atoms, accounting for all of the electrons shown.

       Dative covalent bonding

      A dative covalent bond is formed when both electrons in a covalent bond are provided by the same atom.

       Simple molecular covalent bonding and giant covalent bonding

Schematic illustrations of (a) Bonding in diamond; (b) bonding in silicon dioxide; (c) two-dimensional bonding in graphite, looking down from above; (d) three-dimensional bonding in graphite, looking through the layers.

      The shape of a covalently bonded molecule or ion is determined by the number and arrangement of the pairs of electrons around the central atom. Electron pairs are negatively charged centres and are repelled by neighbouring centres of electron density. The structures formed are most stable when the centres of electron density are as far apart as possible from each other. If you remember this, you will be able to tackle any problems involving the shapes of simple molecules. The process


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