Chemistry AS - Atomic Structure

What it says on the tin - all about AS Chemistry Atomic Structure!


Introduction to my Revision cards

Hi there, budding Chemists!

These revision cards are for AQA AS Chemistry 2009 onwards. (ie. The new specification)

I'm sure if you're on a different exam board they will still be useful.

I'm afraid I can't put diagrams in. So I will set a task at the end of each subtopic, probably to research (ie. Read your notes) a diagram or something to this effect. Like in electronic configuration, as there are lots of things I can't show you on here.

The task may also be working some questions out. You don't have to do them if you don't want to. I will put the answers (and the working out) on a few cards at the back.


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Basic Atomic Structure

Electronic Configuration

An electron has a certain amount of uncertainty as to where it will be from one nanosecond to the next. Using quantum mechanics (but I thought we were Chemists!) for a particular energy of an electron, we can describe the area it is most likely to be in. This is called an orbital.

  • There are 4 types of orbital: s, d, p and f
  • An s orbital is shaped like a ball, 'o'
  • 3 orbitals in a 'p' level of equivelent energy. A bit like '8' and then on their side and diagonal.
  • Each orbital can hold 2 electrons (e-s) because e-s spin and so one will spin up as the other spins down.
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Basic Atomic Structure


  • Electrons fill from the lowest energy sublevels first
  • A sublevel does not exist unless there is an electron occupying it.
  • Orbitals fill singularly in a sublevel before pairing up, due to electron repulsion.

Task: Research the energy sublevel diagram (where you have a graph type thing with energy on the y axis and you draw in the sublevels according to their energy values.)

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Introduction to my Revision Cards

I hope you find these cards useful - it was useful for me to revise writing them!

Last but not least, happy revising...I hope you do well in your test/exam!

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More Electronic Configuration

Writing Electronic configuration without drawing diagrams

Example: Magnesium's electronic configuration (full)

  • Mg: 1s2 2s2 2p6 3s2 (bear in mind that the numbers after the letters should be superscript)

Magnesium's shorthand electronic configuration

  • [Ne] 3s2
  • We use a Noble Gas at the beginning to signify the rest of the electronic configuration.
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Ionic electronic configuration

What about ions?

Ions formed from elements in the 's' or 'p' block of the Periodic table will gain a Noble Gas electronic configuration, ending in a p6.

For transition metal ions, (d block elements) the 4s electrons are removed before the 3d because they are higher in energy.

Task: Write the full and shorthand electronic configurations of:

  • S, Ge, Al, Zn, N, Fe 2+, Rb, Ar, Be, In, Cu, Cl, Tc, I (if you want to do only some, take a range from here, not just the first few)
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Ionisation energies

The First Ionisation energy

X(g) --> X+(g) + e-

The first Ionisation Energy (IE) of an element is the energy required to remove one mole of electrons from one mole of gaseous atoms.

Learn the above. This is an exam/test perfect answer.

There are three factors that affect the ionisation energy.

  • Nuclear charge - the greater the nuclear charge, the greater the 1st IE
  • Atomic radius - the greater the atomic radius, the lower the 1st IE
  • Shielding - the greater the number of inner electrons, the greater the shielding, so the lower the 1st IE
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More Ionisation energies

Generally across a period, the 1st IE increases, this is because the nuclear charge

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