Bonding

Bonding

Describing an atom
1. The atomic number tells you how many protons there are.
2. Atoms of the same element all have the same number of protons.
3. Atoms of different elements will have a different number of protons.
4. To get the number of neutrons, just subtract the atomic number from the mass number.
Compounds are chemically bonded
1. They are formed when atoms of two or more elements are chemically combined together, eg. carbon dioxide.
2. Its difficult to separate the two original elements out again.
Isotopes
1. They are: different atomic forms of the same element, which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS.
2. Isotopes must have the same atomic number but different mass numbers.
3. If they had different atomic numbers, they'd be different elements altogether.
4. Carbon-12 and Carbon-14 are a very popular pair of isotopes.
Ionic bonding
1. Transferring electrons
  1. In ionic bonding, atoms lose or gain electrons to form charged particles (ions) which are strongly attracted to eachother.
2. Ionic compounds have a regular lattice structure
  1. Always have giant lattice structures.
  2. The ions form a closely packed regular lattice arrangement.
  3. There are strong electrostatic forces of attraction between oppositely charged ions, in all directions.
3. Ionic compounds all have similar properties
  1. All have high melting points and high boiling points.
    1. Due to strong attraction between the ions. Takes a lot of energy to overcome this.
  2. When ionic compounds melt, the ions are free to move and they'll carry the electric current.
  3. Dissolve easily in water. Ions separate and are all free to move in the solution, so they carry the electric charge.
Covalent bonding
1. Where atoms share electrons with each other so that they've got full outer shells.
2. Only share electrons with the outer shell (highest energy level)
3. Having a full outer shell gives them the electronic structure of a noble gas.
4. Each covalent bond provides one extra shared electron for each atom.
5. A covalent bond is a shared pair of electrons.
6. Each atom involved has to make enough covalent bonds to fill up its outer shell.
7. Hydrogen
8. Chlorine
9. Methane
10. Hydrogen chloride
11. ammonia
12. Water
13. Oxygen
Metallic
1. Metal properties are all due to the sea of free electrons.
  1. Metals also consist of giant structures.
  2. Free electrons produce all the properties of metals.
  3. These delocalised electrons come from the outer shell of every metal in the structure.
  4. These electrons are free to move through the whole structure making metals good conductors of heat and electricity
  5. These electrons hold the atoms together in a regular structure.
  6. There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
  7. They also form layers of atoms to slide over each other, allowing metals to be bent and shaped.
2. Alloys are harder than pure metals
  1. Pure metals often aren't right for certain jobs. Scientists mix two or more metals together - creating an alloy.
  2. DIfferent elements have different sized atoms. So when another metal is mixed with a pure metal, the new metal will distort they layers.
    1. Harder to slide over each other.
      1. So alloys are harder.

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