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Advanced Higher Chemistry

Advanced Higher Chemistry. Unit 1 Bonding. Bonding & Electronegativity. Below is a simplified description of electronegativity and its effect on bonding. Beware: reliability of ‘electronegativity’ cf water and sodium hydride.

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Advanced Higher Chemistry

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  1. Advanced Higher Chemistry Unit 1 Bonding

  2. Bonding & Electronegativity • Below is a simplified description of electronegativity and its effect on bonding. • Beware: reliability of ‘electronegativity’ cf water and sodium hydride.

  3. Differences in electronegativity values are useful for predicting the type of bonding but are not always correct e.g. calculate the difference in electronegativity values for NaH and H2O.

  4. As both values are the same it could be predicted that they both have the same bonding. • However, NaH is a solid at room temperature and can be electrolysed when it is molten so is ionic. Water has polar covalent bonding. • It is therefore also necessary to look at the properties of a substance to confirm its bonding.

  5. Polar Molecules • Atoms in polar molecules have different electronegativities. • The resulting molecule has a partially positive and a partially negative area.

  6. Covalent Bonding - Hydrogen • As the atoms move together, the nucleus of one atom attracts the electron of the other (drop in potential energy). • If the atoms become too close together the repulsive force between the two nuclei becomes most important and the potential energy increases again. • When the forces of attraction and repulsion balance, the covalent bond is stable.

  7. Covalent Bonding

  8. ro – the bond length. This is the position that the atoms take up when the forces of attraction and repulsion are balanced. • ΔH – the bond dissociation energy. This is the energy released to the surroundings. The same amount of energy must be supplied to break this bond. • The energy required to break one mole of these bonds is known as the bond enthalpy or bond dissociation energy.

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