A positively charged particle located in an atom's
A particle that has no electric charge and is located in an
The central region of an atom where most of the atom's
mass is found in protons and neutrons.
A negatively charged particle located outside an atom's
nucleus. An electron is about 2000 times smaller than
either a proton or neutron.
The number of protons in the nucleus of an atom.
atomic mass number
The total number of protons and neutrons in an atom's
An atom of one element that has a different number
of neutrons than another atom of the same element.
An atom or group of atoms that has a positive or
negative electric charge.
The average mass of the atoms of an element.
A table of the elements, arranged by atomic number,
that shows the patterns in their properties.
A vertical column in the periodic table of the elements.
Elements in a group have similar properties.
A horizontal row in the periodic table of the elements.
Elements in a period have varying properties.
A substance that is present at the beginning of a chemical
reaction and is changed into a new substance.
An element that tends to be shiny, easily shaped, and a
good conductor of electricity and heat.
An element that is not a metal and has properties
generally opposite to those of a metal.
The process by which the nucleus of an atom of an
element releases energy and particles.
The amount of time it takes for half of the nuclei of
a radioactive isotope to decay into atoms of another