Periodic trends

Periodic Trends Overview

  • Periodic trends are patterns that can be observed among elements on the periodic table.
  • These trends arise from the regular increase in proton number and the way electrons fill the atomic orbitals.
  • There exist several key trends including atomic radius, ionisation energy, electron affinity, and electronegativity.

Atomic Radius

  • The atomic radius is half the distance between the nuclei of two atoms of the same element when joined together.
  • Across a period, the atomic radius generally decreases. This is because electrons are added to the same energy level while the positive charge in the nucleus also increases, pulling electrons closer.
  • Down a group, atomic radius increases. This is due to electron being added to a new energy level, farther from the nucleus.

Ionisation Energy

  • Ionisation energy is the energy required to remove an electron from an atom.
  • Across a period, ionisation energy increases. Greater nuclear charge pulls electrons closer to the nucleus making them harder to remove.
  • Down a group, ionisation energy decreases. Electrons are further from the nucleus and shielded by more inner layers, so are easier to remove.

Electron Affinity

  • Electron affinity measures the attraction of an atom for an additional electron, determined by the energy change when an electron is added to a neutral atom.
  • Across a period, electron affinity increases. Atoms with more protons have a stronger pull on additional electrons.
  • Down a group, electron affinity usually decreases. Electrons are added to energy levels further from the nucleus and therefore experience less nuclear pull.

Electronegativity

  • Electronegativity is a measure of how strongly an atom pulls on the electrons in a bond.
  • Across a period, electronegativity increases. With increase in nuclear charge, the pull on bonding electrons becomes stronger.
  • Down a group, electronegativity decreases. Electrons are more distant from the nucleus and are more shielded, hence the pull on bonding electrons is less.

In studying the periodic trends, it’s essential to keep in mind that these are general trends, and some exceptions may occur due to the unique properties of certain elements.