3.1.1 Atomic Structure

• Fundamental particles include protons, neutrons, and electrons.
• Nucleons are protons and neutrons, as they are found in the nucleus.
• The strong nuclear force is the force that holds the protons and neutrons in the centre of the atom, overcoming the electrostatic forces of attraction and repulsion.
• John Dalton suggested in 1803 that elements are composed of indivisible solid spheres.
• JJ Thompson discovered the electron in 1897, showing that they are negatively charged. He proposed the ‘plum pudding model’.
• Ernest Rutherford and his team discovered in 1911 that most of the mass and all the positive charge of an atom is located in a small central nucleus.
• Neils Bohr suggested in 1913 that electrons orbit the nucleus in shells of fixed energy.
• James Chadwick discovered the neutron in 1932.
• Electrons fill the shells closest to the nucleus first.
• Gaining electrons forms negative ions, which have more electrons than protons.
• Losing electrons forms positive ions, which have more protons than electrons.
• The proton number/atomic number (Z) is the number of protons in the nucleus of an atom.
• The mass number (A) is the total number of protons and neutrons in an atom.
• Isotopes are atoms of the same element with different numbers of neutrons, but same number of protons.
• Relative atomic mass (Ar) is the average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12
• Relative molecular mass (Mr) is the average mass of a molecule compared to 1/12th the mass of an atom of carbon-12
• Mass spectrometer is used to identify the abundance and mass/charge ratios of isotopes of an element.
• A time of flight spectrometer is a piece of equipment that analyses a sample and tells you the Ar or Mr. 
• 4 steps in the TOF mass spectrometer: ionisation, acceleration, ion drift and detection.
• Electrospray ionisation

  • the sample is dissolved and pushed through a small nozzle at high pressure.
  • a high voltage is applied to it, causing each particle to gain an H+ ion.
  • The sample is turned into a gas made up of positive ions.
• Electron impact ionisation

  • the sample is vaporised
  • an 'electron gun' is used to fire high energy electrons at it.
  • this knocks an electron off each atom so they become +1 ions.
• Acceleration

  • the positively charged ions are accelerated by an electric field so that they all have the same kinetic energy.
  • This means that the lighter ions will end up moving faster than the heavier ions.
• lon Drift

  • the ions enter a region with no electric field, so they just drift through it.
  • Lighter ions will drift through faster than heavier ions.
• Detection

  • because lighter ions travel at higher speeds in the drift region, they reach the detector more quickly
  • as positive ions hit detector, they gain an electron and this generates a current in the detector
  • more particles that hit the detector at the same time = greater current generated = greater abundance on spectrum.
• M/Z ratio of each peak in a mass spectrum is the same as the relative mass of that isotope.
• Electron shells are made up of subshells, each subshell has atomic orbitals.
• Sub-shell: A group of atomic orbitals of the same type within a shell
• Atomic Orbital: A region within an atom that can hold up to two electrons with opposite spin.
• The s-orbital is spherical shaped and has the lowest energy level.
• The p-orbital is dumbell shaped and has a higher energy level than the s-orbital.
• Group 1 and 2 are in the S-block of the periodic table because their outer electrons are in the S sub-shell
• Group 3-8 are in the P-block of the periodic table because their outer electrons are in the P sub-shell.
• The transition metals are in the D-block of the periodic table because their outer electrons are in the D sub-shell.
• The S sub-shell holds 2 electrons and has 1 orbital.
• The p sub-shell holds 6 electrons and has 3 orbitals.
• The d sub-shell holds 10 electrons and has 5 orbitals.
• The 4s sub-shell fills up before the 3d sub-shell because the 4s sub-shell is at a lower energy level.
• When transition metals become ions they lose electrons from their 4s sub-shell before their 3d electrons.
• The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atom to form one mole of gaseous +1 ions.
• What is the equation for the 1st ionisation energy of sodium?

  Na (g) → Na+ (g) + e-