Chemistry

Term 1

Emission spectra

Spectra obtained due to radiations emitted by excited atoms.

Absorption spectra

Spectra obtained when atoms absorb energy.

Electronegativity

The tendency of an atom to bond with another using shared electrons, reflecting its ability to attract electrons in a chemical bond.

First ionisation energy

The minimum energy required to remove the outermost electron from a neutral atom in its gaseous state.

Atomic number

The number of protons in an atom, represented as Z.

Atomic mass

The mass of an atom, usually measured in atomic mass units (AMU).

Neutrons

Calculated as atomic mass (AMU) minus atomic number (Z).

Protons

Identical to the atomic number (Z).

Electrons

Also equal to the atomic number (Z).

Alpha decay

A process where an alpha particle (2 protons and 2 neutrons) is emitted from an atom's nucleus, resulting in a new element with an atomic number reduced by 2.

Beta Minus decay

A decay process where a neutron transforms into a proton while emitting a beta particle (an electron) and an antineutrino.

Beta Plus decay

A decay process where a proton transforms into a neutron while emitting a positron.

Atomic radius

The size of an atom, which decreases across a period and increases down a group.

Shielding effect

The phenomenon where inner electrons block the attractive force from the nucleus to the outer electrons.

Noble gases

Elements that have zero valent electrons, leading to low reactivity.

Group number

Corresponds to the number of valence electrons for main group elements, determining chemical reactivity.

Energy levels

Also called SDPF, referring to the different energies that electrons can occupy.

What affects electronegativity across a period

Electronegativity increases across a period due to a combination of increased nuclear charge and decreasing atomic radius.

What affects electronegativity down a group

Electronegativity decreases as you move down a group in the periodic table because the increased atomic size and enhanced shielding effect

Down a group, first ionisation energy

generally decreases due to increased atomic radius and shielding and the increased amount of electrons in different energy levels

Across a period, first ionisation energy

amount of electrons remain in the same energy level, decreasing the atomic radius therefore increasing the first ionisation energy.