Atomic Structure

Atomic Structure

1. The Atom

   • Atoms are made up of protons, neutrons, and electrons
   • Electrons have a -1 charge. They are in orbitals which take up most of the volume of the atom
   • Most of the mass of the atom is concentrated in the nucleus. The diameter of the nucleus is tiny compared to the rest of the atom. You find protons and neutrons in the nucleus
   • For neutral atoms which have no overall charge, the number of electrons is the same as the number of protons. The number of neutrons is the mass number - the atomic number

2. Models of Atomic Structure

   • 1) 19th century John Dalton described atoms as solid spheres, and said that the different spheres made up the different elements
   • 2) 1897: J.J Thompson discovered the electron, plumb pudding model
   • 3) 1909: Rutherford conducted his gold foil experiment. Fired positively charged alpha particles at a very thin sheet of gold. Proved that most of the atom is empty space
   • 4) Scientists realised that electrons in a "cloud" around the nucleus of an atom would quickly spiral down causing the atom to collapse. BOHR proposed a new model of the atom where electrons exist in shells or orbits of fixed energy.
   • 5) Not all electrons in a shell have the same energy. Refined to include sub-shells.

3. RAM and Mass Spec

   • Relative masses are masses of atoms compared to carbon-12: RAM = the average mass of an atom of an element on a scale where an atom of carbon-12 is 12, Relative Isotopic mass = mass of an atom of an isotope of an element where an atom of Carbon-12 is 12, Mr = the average mass of a molecule on a scale where an atom of carbon-12 is 12
   • Relative masses can be measured using a mass spectrometer

4. Electronic Structure

   • Electron shells are made up of sub-shells and orbitals
   • Fill the lowest energy levels first: 1s, 2s, 2p, 3s, 3p, 4s, 3d
   • Electronic structure decides the chemical properties of an element: Groups 1 & 2 are in the S block , Groups 5,6 & 7 are in the P block

5. Ionisation Energy

   • Trends

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