Moodle

• Going across a period, nuclear charge decreases.
• Going across a period, distance between the outermost electron and the nucleus decreases.
• Going across a period, shielding stays the same.
• Down a group, shielding increases.
• Down a group, nuclear charge increases.
• Down a group, distance between the outermost electron and the nucleus increases.
• Ionisation energy always decreases down a group.
• Atomic number is the number of protons in the nucleus.
• Mass number is the number of protons and neutrons in the nucleus.
• Relative isotopic mass is the mass of an atom of an isotope compared with 1/12 the mass of one atom of C-12.
• Relative atomic mass is the weighted mean mass of an atom of an element compared with 1/12th the mass of one atom of C-12.
• Al has a lower first ionisation energy than Mg because the outermost electron of Al is in a different subshell, further from the nucleus than the outermost electron in Mg.
• First ionisation energy is the energy required to remove one mole of electrons from one mole of atoms to create one mole of +1 ions in the gaseous state.