That which has mass and occupies space.
An artifact that is one of the individual parts of which a composite entity is made up.
A substance formed by chemical union of two or more elements or ingredients in definite proportion by weight.
An element indispensable for life but required in extremely minimum amounts.
The smallest component of an element having the chemical properties of the element.
The particles of the nucleus that have no charge.
Positively charged particles located in the nucleus.
Negatively charged particles found outside the nucleus.
An atom's dense central core, containing protons and neutrons.
A measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.
The order of an element in Mendeleyev's table of the elements.
The sum of the number of neutrons and protons in an atomic nucleus.
Total mass of the protons and neutrons in an atom, measured in atomic mass units.
Atoms of the same element that have different numbers of neutrons.
Isotope in which the nucleus decays (breaks down) over time, giving off radiation in the form of matter and energy.
An exertion of force.
Energy stored due to an object's position or arrangement.
An energy level representing the distance of an electron from the nucleus of an atom.
Electrons on the outermost energy level of an atom.
The outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom.
A region in an atom where there is a high probability of finding electrons.
An electrical force linking atoms.
A chemical bond that involves sharing a pair of electrons between atoms in a molecule.
The simplest structural unit of an element or compound
A bond formed when two atoms share a pair of electrons.