S1L4: Atomic Mass

Atomic Number

The top number on an element that determines the number of protons in its nucleus.

Isotopes

Atoms with the same number of protons but a different number of neutrons.

Mass Number

The total number of protons and neutrons in the nucleus of an atom.

Neutrons Calculation

Subtracting the atomic number from the mass number gives the number of neutrons.

Atomic Mass Unit (amu)

A mass equal to 1/12th the mass of a carbon-12 atom, used for measuring protons, neutrons, and electrons.

Carbon-12

The reference standard atom chosen by scientists to compare all other atomic masses.

Period

A horizontal row in the periodic table, with a total of 7 periods.

Group

A vertical column in the periodic table based on the organization of outer shell electrons.

Periodic Trends

The arrangement of elements in the periodic table that reveals different aspects and patterns.

Atomic Radius

The distance from the nucleus to the outer shell of an atom.

Ionization Energy

The energy required to remove an electron from an atom.

Ionization Energy Trend

Generally increases from the bottom left to the top right of the periodic table.

Electron Affinity

The energy change associated with a neutral atom gaining an electron, increasing from bottom left to top right on the periodic table.

Metallic Character

The reactivity of a metal based on how easily it can lose an electron.

Electronegativity

The degree to which elements in covalent bonds attract shared electrons.

General Trend

Most trends in the periodic table increase from bottom left to top right.

Percent Natural Abundance

The relative amount of an element found in nature.

Average Atomic Mass

Calculated as Isotope A(amu x percent abundance) + Isotope B(amu x percent abundance), with percent abundance as a decimal.

Radioactivity

The spontaneous emission of radiation in the form of particles or high-energy photons due to a nuclear reaction.

Unstable Isotopes

All unstable isotopes are radioactive.

Decay Product

The final product formed as a radioisotope decays or decomposes.

Energy Levels (Electron Shells)

Fixed energies associated with average distances from the nucleus where electrons are found.

Electron Shell Capacities

Energy Level 1 holds a maximum of 2 electrons, and Energy Level 2 holds a maximum of 8 electrons.

Orbitals

Regions of space where the probability of finding an electron is very high, with varying shapes.

Electronic Configuration

A map showing the likely locations and distribution of electrons in an atom.

Aufbau Principle

The rule stating that electrons occupy orbitals from lowest energy to highest.

Ground State

The lowest energy state of a nucleus, atom, or molecule.