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C3 Atoms, elements and compounds(Ian) (Bonding (Molecules and covalent…

- - - - Example. Change in states of water – water changes its state from solid to liquid to gas
        without a change in the fundamental composition of matter
  - - - Example. Water undergoes decomposition to give back its elemental state – oxygen and hydrogen upon application of electric current.The fundamental composition of particles changes and hence decomposition of water is described as a chemical change..
- - - - Electron(电子) 1/2000(relative mass) -1(relative charge)
      - Proton(质子) 1(relative mass) +1(relative charge)
      - Neutron(中子) 1(relative mass) 0(relative charge)
      - Since an atom is neutral, the number of protons should be equal the number of electrons
- - - - 1.When two non-metal atoms react together, both need to gain electrons to achieve stable outer shells. They manage this by sharing electrons.
      - 2.Each hydrogen atom has a positive nucleus. Both nuclei attract the shared electrons – and this strong force of attraction holds the two atoms together.
      - 3.This force of attraction is called a covalent bond.
      - 4.A single covalent bond is formed when atoms share one pair of electrons.
      - 5.A molecule is a group of atoms held together by covalent bonds.
  - - - Allotropes of carbons*: not all covalent solids are molecular.
      - Diamond and GraphiteBoth diamond and graphite are made only of carbon atoms. So diamond and graphite are allotropes of carbon – two forms of the same element.
      - Structure: (Diamond)strong covalent bonds (a carbon atom forms covalent bonds to four others).
      - Properties and reasons: strong covalent bonds between carbon atoms (very hard and very low m.p.)
      - Uses: cutting /drilling
      - Structure:(Graphite) weak forces (each carbon atom forms covalent bonds to three others.
      - Properties and reasons: weak forces between layers easy to slide over each other(slippery), it only forms three bonds and one e- is free(conduct electricity).
      - Uses: lubricant, electrical conductor (to move delocalised).
  - - - 1.An atom becomes an ion when it loses or gains electrons. 2.An ion is a changed particle. It is charged because it has an unequal number of protons and electrons.
      - 3.Ionic bonds are the strong electrostatic attraction between cations and ions.
      - 4.In an ionic compound, the cations and anions are packed together in a way to maximize the attractions.
      - 5.Lattice structure of ionic compounds: regular arrangement of alternating positive and negative ions.
      - 6.A metal reacts with a non-metal to form an ionic compound. The metal atoms lose electrons. The non-metal atoms gain them. The ions form a lattice. The compound has no overall charge.