Chemistry - C2.1 - Structure and Bonding

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C2.1.1 - Chemical Bonding

  • Two or more elements joined together = compound - atoms of elements join together by sharing or transferring electrons to achieve stable electronic structures - noble gas elements have stable electronic structures
  • Covalent - non-metallic elements join together by sharing electrons
  • Ionic - metallic + non-metallic join together - metallic element loses electrons = positive ion, non-metallic element gains electrons = negative ion - oppositely charged ions attract each other
  • Group 1 elements - one electron on highest occupied energy level (outer shell)
  • Group 7 elements - seven electrons in highest occupied energy level
  • Sodium chloride - compound with equal numbers of sodium and chloride ions - NaCl
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C2.1.2 - Ionic Bonding

  • Holds oppositely charged ions together in giant structure - very regular as ions pack together neatly
  • Strong electrostatic forces of attraction in all directions - each ion in the giant structure/lattice is surrounded by oppositely charged ions - held firmly in place
  • NaCl - equal numbers of sodium and chloride ions - ions alternate to form a cube lattice
  • Ratio of different ions depends on charge - eg. calcium ions = Ca2+, chloride ions = Cl- - double the amount of chloride ions - CaCl2
  • Dot and cross diagrams - used to representatoms and ions involved in ionic bonding - only show electrons on outer shells
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C2.1.3 - Formulae of Ionic Compounds

  • Ionic compounds - neutral - know charge on each ion = work out formula by balancing charges
  • Charge on simple ions formed by elements in main groups of periodic table can be worked out by group no
  • Transition metals - charge shown on ion by roman numeral in compound name - eg. iron(II) sulfate contains Fe2+
  • Some ions made from more then one element, eg. carbonate ions = CO3 2+, hydroxide ions = OH- - if multiplying, use brackets - calcium hydroxide = Ca(OH)2
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C2.1.4 - Covalent Bonding

  • Atoms of non-metals need to gain electrons - do this by sharing electrons with other atoms - each shared pair of electrons strongly attracts atoms forming a covalent bond - atoms held together by covalent bonds = molecules
  • Group 7 - need one electron = one covalent bond, group 6 - need two electrons = two covalent bonds etc.
  • Covalent bond only acts between atoms it bonds together - so many covalently bonded substances consist of small molecules
  • Some atoms, eg. carbon, can form several bonds - can join together in giant covalent structure - sometimes called macromolecules
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C2.1.5 - Metals

  • Atoms in metallic elements are the same size - form giant structures where atoms are layered in regular patterns
  • When metal atoms pack together, electrons in outer shell become delocalised and move freely between atoms - produces positive ions in sea of moving electrons
  • Ions are positive, electrons are negative - delocalised electrons strongly attract ions and hold giant structure together
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