Chemistry AS & A Level: Atomic Structure and Electrons in Atoms

Vocabulary flashcards covering core definitions and terms from Chapter 1 (Atomic structure) and Chapter 2 (Electrons in atoms).

Atom

The smallest part of an element that can take part in a chemical change.

Nucleus

The tiny region in the centre of an atom containing protons and neutrons where nearly all of its mass is concentrated.

Nucleons

The subatomic particles (protons and neutrons) present in the nucleus of an atom.

Atomic number (proton number)

The number of protons in the nucleus of an atom, represented by the symbol $Z$.

Mass number (nucleon number)

The total number of protons plus neutrons in the nucleus of an atom, represented by the symbol $A$.

Isotopes

Atoms of the same element that have different numbers of neutrons and therefore different mass numbers.

Ions

Electrically charged particles formed by the loss or gain of electrons from an atom or group of covalently bonded atoms.

First ionisation energy

The energy needed to remove one electron from each atom in one mole of atoms of the element in the gaseous state to form one mole of gaseous $1+$ ions.

Second ionisation energy

The energy needed to remove one electron from each ion in one mole of gaseous $1+$ ions to form one mole of gaseous $2+$ ions.

Successive ionisation energies

The sequence of ionisation energies required to remove electrons one by one from an atom until only the nucleus is left.

Shielding effect

The repulsion of outer-shell electrons by full inner shells of electrons, which reduces the attractive force felt from the positive nuclear charge.

Principal quantum shells

The main energy levels outside the nucleus (designated by symbol $n$) numbered according to how far they are from the nucleus.

Atomic orbital

A region of space around the nucleus of an atom that can be occupied by one or two electrons.

Spin-pair repulsion

The repulsion between two electrons occupying the same atomic orbital in a sub-shell, which makes it easier to remove one of the paired electrons.

Free radical

A species with one or more unpaired electrons.