Bonding

Bonding

1. Describing an atom

   • The atomic number tells you how many protons there are.
   • Atoms of the same element all have the same number of protons.
   • Atoms of different elements will have a different number of protons.
   • To get the number of neutrons, just subtract the atomic number from the mass number.

2. Compounds are chemically bonded

   • They are formed when atoms of two or more elements are chemically combined together, eg. carbon dioxide.
   • Its difficult to separate the two original elements out again.

3. Isotopes

   • They are: different atomic forms of the same element, which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS.
   • Isotopes must have the same atomic number but different mass numbers.
   • If they had different atomic numbers, they'd be different elements altogether.
   • Carbon-12 and Carbon-14 are a very popular pair of isotopes.

4. Ionic bonding

   • Transferring electrons
     • In ionic bonding, atoms lose or gain electrons to form charged particles (ions) which are strongly attracted to eachother.
   • Ionic compounds have a regular lattice structure
     • Always have giant lattice structures.
     • The ions form a closely packed regular lattice arrangement.
     • There are strong electrostatic forces of attraction between oppositely charged ions, in all directions.
   • Ionic compounds all have similar properties
     • All have high melting points and high boiling points.
       • Due to strong attraction between the ions. Takes a lot of energy to overcome this.
     • When ionic compounds melt, the ions are free to move and they'll carry the electric current.
     • Dissolve easily in water. Ions separate and are all free to move in the solution, so they carry the electric charge.

5. Covalent bonding

   • Where atoms share electrons with each other so that they've got full outer shells.
   • Only share electrons with the outer shell (highest energy level)
   • Having a full outer shell gives them the electronic structure of a noble gas.
   • Each covalent bond provides one extra shared electron for each atom.
   • A covalent bond is a shared pair of electrons.
   • Each atom involved has to make enough covalent bonds to fill up its outer shell.
   • Hydrogen
   • Chlorine
   • Methane
   • Hydrogen chloride
   • ammonia
   • Water
   • Oxygen

6. Metallic

   • Metal properties are all due to the sea of free electrons.
     • Metals also consist of giant structures.
     • Free electrons produce all the properties of metals.
     • These delocalised electrons come from the outer shell of every metal in the structure.
     • These electrons are free to move through the whole structure making metals good conductors of heat and electricity
     • These electrons hold the atoms together in a regular structure.
     • There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
     • They also form layers of atoms to slide over each other, allowing metals to be bent and shaped.
   • Alloys are harder than pure metals
     • Pure metals often aren't right for certain jobs. Scientists mix two or more metals together - creating an alloy.
     • DIfferent elements have different sized atoms. So when another metal is mixed with a pure metal, the new metal will distort they layers.
       • Harder to slide over each other.
         • So alloys are harder.