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Ionic compounds
Formed by loss or gain of electrons.
Held together by strong electrostatic charges.
In a regular repeating lattice structure.
Often form crystals
Ionic compounds are neutral, so made of a negative charged and positive charged ions (*never write atoms)
Features of ionic compounds
High boiling and melting points due to strong electrostatic bonds.
Conduct electricity when molten or dissolved in water, but not solid- particles must be charged and free to move around.
It is important to remember that it is the ions moving that enable ionic compounds to conduct electricity and that it is NOT electrons moving.
Covalent bonds
Molecular substances are held together by using covalent bonds
Usually form between non metals
Are produced by sharing pairs of electrons
How to find molecular formula
1) find out how many electrons the atom needs to make a full outer shell.
2) this number is the same as the valency.
3) match up the number of valencys (if hydrogen has a valency of 1, and oxygen has a valency of 2, 1 x 2 = 2 which Is equal to the oxygen valency of 2- so the answer is H2O
What is a molecule?
A molecule is when 2 or more atoms of an element is chemically joined.
What is the difference from a molecule and a compound?
A molecule is when 2 or more atoms of an element is chemically joined. Are groups of atoms joined by covalent bonds. Molecules can be compounds or elements
Molecule example: -water (H2O) -oxygen (O2)
Compound example: -salt (NaCl) -water (H2O)
Allotropes of carbon- fullerenes
Carbon atoms are covalently bonded to 3 or more carbon atoms
Often tubular molecules (nanotubes) or spherical- eg buckmibsterfullerene (or Bucky ball) which has 60 carbon atoms that form a ball with the formula C60.
Allotropes of carbon- Graphene
Similar to fullerenes but is not a simple molecule.
Consists of a sheet of carbon atoms with no fixed formula.
Sheet is just one atom thick but it’s bonds make it extremely strong.
Also allows free electrons to move across surface so it is a good electrical conductor.
GRAPHENE- a single sheet of carbon with free electrons that can conduct electricity.
Often tubular molecules (nanotubes) or spherical- eg buckminsterfullerene (or Bucky ball) which has 60 carbon atoms that form a ball with the formula C60.
Is soft and slippery due to strong bonds within molecule but weak forces between molecules.
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