AS-Level Chemistry: Unit 1:The Atom

The Structure of an Atom
1. atoms form everything in our universe.
  1. They consist of three particles: the proton, neutron and electron.
    1. electrons have a -1 charge.
      1. electrons 'whizz' around the nucleus of the atom in 'orbitals'.
      2. their relative mass is: 1/2000
    2. protons have a +1 charge
      1. Relative mass: 1
    3. neutrons don't have a charge!
      1. Relative mass: 1
Nuclear Symbols
1. you can work out the no. of protons, neutrons and electrons from the nuclear symbol
2. mass number: the number of protons and neutrons in the atom's nucleus
3. atomic (proton) number: number of protons in the atom.
  1. all atoms of the same element have the same proton number!
Atoms and Ions
1. neutral atoms (no charge) have the same electron and proton number.
2. the neutron number is just the mass no. minus the atomic no., i.e. "the top minus the bottom" (Nuclear Symbols)
3. Ions
  1. Ions have different no. of protons and electrons.
  2. Negative ions (e.g. Br-) have more electrons than protons.
  3. Positive ions (e.g. Mg2+) have more protons than electrons.
  4. Exam Tip: Ions
    1. Ions are easy to spot: they always have a plus or minus charge (+ or -) next to them! If the charge is a plus, it means an electron has been lost, e.g. Mg2+ means that the Magnesium ion has lost two electrons. If there is a minus sign, it means electrons have been gained. For example, 3- means 3 electrons have been lost!
Isotopes
1. isotope isn't just a scary science word, nope! Isotopes of an element are atoms with the same proton no., but different neutron number.
  1. basically atoms with the same no. of protons but different neutron no. are isotopes.
  2. different isotopes of the same element react (chemically) the same way

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4 comments

Sayda Eiliya

about 8 years ago

3- means 3 electron gained

s0120054325

over 9 years ago

Actually the mass of an electron is 1/1840 not 1/2000 this needs to be amended or people will lose marks in exams for writing this

orporman

about 10 years ago

Would like to clarify, in the exam tip at the bottom it says 3- is 3 electrons lost, it's actually 3 electrons gained, because the atom becomes negative as more electrons are gained.