Trends in the Periodic Table - Vocabulary

Vocabulary flashcards covering atomic radius, covalent radius, screening effect, nuclear charge, ionisation energies (first and second), energy levels evidence, Be/B and N/O dip explanations, potassium ionisation pattern, electronegativity, and group trends.

Atomic radius

Half the distance between the nuclei of two identical atoms joined by a single covalent bond.

Covalent radius

A measurement of an atom's size based on half the distance between two covalently bonded identical atoms; used to compare sizes in molecules.

Screening effect

The shielding of outer electrons from the nucleus by inner electron shells, reducing the effective nuclear attraction.

Nuclear charge

The total positive charge of the nucleus (number of protons) pulling on electrons.

First ionisation energy

The minimum energy required to remove the most loosely bound electron from a neutral gaseous atom.

Second ionisation energy

The energy required to remove an electron from a singly charged positive ion (a +1 ion) in the gaseous state.

Ionisation energy trend down a group

Decreases down a group because atomic radius grows and screening effect increases, making it easier to remove an electron.

Ionisation energy trend across a period

Increases across a period (main group) due to increasing nuclear charge with little additional shielding and decreasing atomic radius.

Be to B dip in ionisation energy

From Be to B, the outer shell changes from full 2s to partially filled 2p, giving Be a higher IE; B’s IE is lower due to a less stable outer sublevel.

N to O dip in ionisation energy

N has a half-filled 2p subshell (2p3), while O (2p4) disrupts that stability, causing a drop in IE from N to O.

Potassium successive ionisation pattern

First ionisation removes the outermost electron from n=4; subsequent removals come from closer shells (n=3, then n=2, then n=1), with large energy jumps between shells.

Alkali metals (Group 1) reactivity trend

Very reactive due to having one electron in the outer shell; reactivity increases down the group because atomic radius increases.

Halogens (Group 7) reactivity trend

Very reactive because they need one electron to complete the outer shell; reactivity generally decreases down the group as electronegativity decreases.

Electronegativity

Relative attraction of an atom in a molecule for the shared electrons in a covalent bond.

Electronegativity trend down group

Decreases down a group due to increasing atomic radius and screening.

Electronegativity trend across period

Increases across a period due to rising nuclear charge and decreasing atomic radius.

Atomic radius trend summary

Increases down a group and decreases across a period for covalent radii.

Evidence for energy levels in successive ionisation

Large increases in successive ionisation energies occur when electrons are removed from inner shells, revealing the energy level structure.