Bonding and structure

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Ionic bonding

  • Atoms lose or gain electrons to form charged particles called ions which are strongly attractde to one another because of their opposite charges
  • Ionic bonding is normally found between a metal and a non metal

Group 1     2      3      4     5      6     7   8 

Ion     +     2+    3+    0     3-    2-    -     0

  • Atoms that gain electrons become negatively charged ions
  • Atoms that lose electrons become positively charged ions
  • Ions have the electron arrangement of a noble gas (group 0)
  • Metals form positive ions & non metals form negative ions
  • The alkali metals (group 1) react with non-metals to form ionic compounds in which the metal ion has a single positive charge
  • The halogens (group 7) react with metals to form ionic compounds in while the halide ions have a single negative charge
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Ionic bonding - simple molecules

  • Substances that consist of simple molecules are gasses, liquids or solids that have relatively low melting and boiling points because the weak intermolecular forces are easily overcome, not the bonds
  • Do not conduct electricity because the molecules do not have an overall charge


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Ionic compounds

  • An ionic compound is a giant structure of ions
  • Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions
  • These forces act in all directions in the lattice 


  • Giant ionic lattices have high melting and boiling points because of the large amounds of energy needed to break the many strong bonds
  • Conduct electricity when melted/dissolved in water because the ions are free to move and carry the current
  • Self organising & brittle
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Covalent bonding

  • A covalent bond is a shared pair of electrons usually between two non-metals
  • They only share electrons in their outer shells
  • The atoms form very stronng covalent bonds
  • Simple covalent molecules consist of 2 or more atoms joined by covalent bonds
  • The forces between these molecules are very weak
  • Weak intermolecular forces mean low melting and boiling points


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Giant covalent structures


  • Macromolecules eg diamond and graphite (forms of carbon) and silicon dioxide (silica) 
  • All the atoms in these structures are linked to other atoms by strong covalent bonds -  they have very high melting points
  • In diamond, each carbon atom forms 4 covalent bonds with other carbon atoms in a giant covalent structure so diamond is very hard
  • In graphite, each carbon atom bonds to 3 others forming layers which are free to slide over eachother because there are no covalent bonds between the layers so graphite is soft
  • In graphite one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity 
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  • Nano = one thousand milionth
  • Refers to structures that are 1-100nm in size, of the order of a few hundred atoms
  • Nanoparticles show properties different from those for the same materials in bulk and have a high surface area to volume ratio,

Uses: coatings, cosmetics such as suntan creams and deodorants, medicine - delivering drugs, sport, silver nanoparticles are antibacterial

Development: new computers, new catalysts, highly selective sensors, stronger and lighter construction materials

Risks: breathing in tiny particles could damage lungs, could enter the bloodstream, could have unpredictable effects in cosmetics

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  • Carbon can also form fullerenes with different numbers of carbon atoms
  • Can be used for drug delivery in the body, in lubricants, as catalysts and in nanotubes for reinforcing materials


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