3.1.1 Atomic Structure Overview
3.1.1.1: Fundamental particles
Understanding of atomic structure changed over time:
Dalton: atoms are small invisible particles
Electrons discovered: Thompson’s Plum Pudding Model: ball of positive change with negative electrons evenly scattered within it
Alpha particle scattering experiment: Rutherford’s nuclear model: tiny positive nucleus at centre, mostly empty space, cloud of electrons
Bohr model: electrons orbit in shells
Relative masses:
Proton: 1 Neutron: 1 Electron: 1/1840 , very small
Relative charges:
Proton: +1 Neutron: 0 Electron: -1
An atom consists of a nucleus containing protons and neutrons surrounded by electrons.
3.1.1.2: Mass number and isotopes
Mass number: sum of protons and neutrons
Atomic number: number of protons
Explain existence of isotopes: Atoms of the same element with the same atomic number, but a different number of neutrons, and thus a different mass number.
Neutral atoms of isotopes will chemically react the same, as they have the same proton number, but will have different physical properties due to the different neutron amount.
Time of Flight mass spectrometry:
Ionisation: Sample of an element is vaporised and injected into a mass spectrometer, as high voltage is passed through, causing electrons to be removed- leaving +1 ions.
Acceleration: Positively charged ions are accelerated towards a negatively charged detection plate.
Ion drift: Ions are deflected by a magnetic field in a curved path.
Detection: When the positive ions hit the negatively charged plate, they gain an electron, and produce a flow of charge. The greater the abundance, the greater the current produced.
Analysis: Using Ke=½ mv², you can determine the mass of the sample.
Mass spectrometry: Analysis technique, used to identify different isotopes and find the overall relative atomic mass of the element.
Using mass spec:
Relative atomic mass (Ar) : m/z x abundance / total abundance
m/z (mass to charge ratio) = x axis
abundance= y axis
3.1.1.3: Electron configuration