bonding and structure

• a molecule is a particle made up of a specified number of atoms that are covalently bonded together
• an ionic bond is the electrostatic attraction between oppositely charged ions
• a covalent bond is a strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• a lattice is a regular arrangement of atoms, ions or molecules in a solid
• giant ionic structure is a giant lattice that consists of alternately arranged positive and negative ions. Strong electrostatic forces between the oppositely charged ions result in these compounds having high melting points
• giant covalent structure is a giant lattice of atoms that consists of strong covalent bonds linking every atom to several others in a giant structure that goes on indefinitely.
• a giant metallic structure is a giant lattice that consists of many layers of close-packed metal ions. these atoms lose their outer-shell electrons to become positive ions. the lattice is held together by the strong electrostatic forces between the delocalised electrons and positive ions.
• properties of giant metallic structures:

  • ductile
  • malleable
  • high melting and boiling points
  • conducts when solid and molten
  • insoluble in water and non-polar solvents
• properties of giant ionic structures:

  • brittle
  • high melting and boiling points
  • conducts when molten or dissolved
  • soluble in water
  • insoluble in non-polar solvents
• properties of giant covalent structures:

  • high melting and boiling points
  • insoluble in water and non-polar solvents
  • no conduction of electricity (only graphite)
• properties of simple molecular structures:

  • low melting and boiling points
  • soluble in water and non-polar solvents
  • no conduction of electricity
• elements have a tendency to bond so that they acquire a noble gas configuration which is energetically stable
• in a giant ionic lattice each ion is surrounded by oppositely charged ions to create a stable 3D structure
• ionic lattices are soluble in polar solvents as they break down the ionic lattice by surrounding each ion to form a solution, the slight charges within the polar substance are able to attract the charge ions in the giant ionic lattice
• a lone pair of electrons gives a concentrated region of negative charge around the atom
• in oxygen molecules there are double covalent bonds between the two oxygen atoms
• in nitrogen there is a triple covalent bond between the two nitrogen atoms in the molecule
• average bond enthalpy is the mean energy needed for 1 mole of a given type of gaseous bonds to undergo homolytic fission
• a dative covalent bond or coordinate bond is when one of the atoms supplies both the shared electrons to the covalent bond
• the direction of the arrow on a dative covalent bond shows the direction in which the electron pair has been donated
• for elements in groups 15-17 of the periodic table more of the outer-shell electrons are able to take part in bonding and this causes one of the bonding atoms to have more than 8 electrons in its outer shell which is the expansion of the octet
• atoms of non-metals in group 15 can from 3 to 5 covalent bonds depending on how many electrons are used in bonding
• atoms of non-metals in group 16 can form 2, 4 or 6 covalent bonds depending on how many electrons are used in bonding
• atoms of non-metals in group 17 can form 1, 3, 5 or 7 covalent bonds depending on how many electrons are used in bonding
• unpaired electrons pair up into lone pairs and the maximum number of electrons that can pair up is equivalent to the number of electrons in the outer shell
• electronegativity is a measure of the attraction of an electron pair in a covalent bond
• electronegativity increases towards fluorine from all directions
• ice is less dense than water as when ice forms water molecules arrange themselves into an open lattice structure which holds the water molecules apart, when ice melts the rigid hydrogen bonds collapse and the molecules move closer together
• water's boiling and melting points are much higher than expected as it contains hydrogen bonds which are much stronger than other intermolecular forces, this means they require much more energy to overcome and break these bonds
• the strength of hydrogen bonds also explains the relatively high surface tension and viscosity of water
• giant metallic structures are ductile so can be drawn out or stretched into wires
• giant metallic structures are malleable and can be hammered into thin sheets and different shapes
• delocalised electrons are responsible for giant metallic structures being ductile and malleable as they can move which gives the lattice a degree of give and this allows layers of atoms to slide past each other