chapter 2 : atomic structure

• Subatomic particles

  • Protons
  • Neutrons
  • Electrons
• How protons behave in an electric field

  Deflected towards the negative plate
• How neutrons behave in an electric field

  Not affected due to lack of charge
• How electrons behave in an electric field

  Deflected towards the positive plate, greater deflection than protons due to smaller mass
• Most of the mass of an atom is concentrated in the nucleus
• Atomic number

  Number of protons in the nucleus of an atom
• Mass number

  Sum of the numbers of protons and neutrons in the nucleus of an atom
• In a neutral atom, the atomic number is the same as the number of electrons
• Isotopes

  Atoms of the same element with the same number of protons but a different number of neutrons
• Orbital

  A region that holds up to 2 electrons, with opposite spin
• 1. orbital

  • Spherical shape
• 1. orbital

  • Dumb-bell shape
• Subshell

  A division of electron shells into different orbitals (s, p, d, and f)
• Rules for filling up orbitals

  1. Electrons always occupy the lowest energy orbital available

  2. Electrons only pair up when there are no empty orbitals of the same energy level as the half-filled orbitals
• Number of orbitals and electrons in each subshell

  • s-subshell: 1 orbital / 2 electrons
  • p-subshell: 3 orbitals / 6 electrons
  • d-subshell: 5 orbitals / 10 electrons
  • f-subshell: 7 orbitals / 14 electrons
• s has the lowest energy and d has the highest energy
• Subshells found in shells 1 to 4, and maximum number of electrons in each shell

  • Shell 1: s, 2 electrons
  • Shell 2: s, p, 8 electrons
  • Shell 3: s, p, d, 18 electrons
  • Shell 4: s, p, d, f, 32 electrons
• Order of filling up subshells

  Follow the arrow
• Principal quantum number (n)

  Represents the shell that electrons occupy, the larger n the higher the energy and further from the nucleus
• The periodic table is divided into s, p, d and f blocks based on the subshell containing the valence electrons
• First ionisation energy


  The energy required to remove an electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
• First ionisation energy is endothermic
• How successive ionisation energies tell you which group an element belongs to

  Look for a large increase between two different successive ionisation energies, indicating the 8th electron is being taken from a new, full, stable shell, so the element belongs to group 7
• First ionisation energy increases across periods 2 and 3
• First ionisation energy decreases down a group
• Electron affinity

  The enthalpy change that accompanies the addition of 1 electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions