Chemistry Fundamentals: Atomic Mass and Isotopes

Practice flashcards covering the definition of the unified atomic mass unit, the masses of subatomic particles, atomic numbers, isotopes, and the difference between average and relative atomic mass.

Unified atomic mass unit

A unit of mass defined as $1.66054027 \times 10^{-27}\,\text{kg}$.

Mass of a proton

Approximately $1$ unified atomic mass unit, more specifically about $1.007$ atomic mass units.

Mass of a neutron

Approximately $1$ unified atomic mass unit, more specifically about $1.008$, which is slightly more than the mass of a proton.

Mass of an electron

A mass that is far smaller than a proton or neutron, approximately two thousandth ($1/2000$) of their mass.

Atomic number

The number that tells you how many protons an atom has, which defines the identity of the element.

Isotopes

Versions of a given element that have the same number of protons but different numbers of neutrons.

Average atomic mass

A number calculated as the weighted average of the various isotopes for a given element.

Atomic weight

An older term for average atomic mass commonly used in older chemistry textbooks.

Relative atomic mass

A unitless number on the periodic table that expresses the average mass of an atom relative to others (e.g., carbon is roughly $12$ times heavier than hydrogen).

Hydrogen-1 abundance

Roughly $99.98\%$ of the hydrogen in the universe, consisting of one proton and zero neutrons.