Physical Science, Unit 4: Atoms and Periodic Table, Vocabulary
Atomic Number
The number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element.
Atom
The smallest unit of an element that maintains the properties of that element.
Electron Cloud
A region around the nucleus of an atom where electrons are likely to be found.
Electron
A subatomic particle that has a negative charge.
Neutron
A subatomic particle that has no charge and that is located in the nucleus of an atom.
Proton
A subatomic particle that has positive charge and that is located in the nucleus of an atom; the number of protons in the nucleus is the atomic number, which determines the identity of the element.
Atomic Mass Unit
A unit of mass that describes the mass of an atom or molecule.
Group
A vertical column of elements in the periodic table; elements in a group share chemical properties.
Isotope
An atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)
Halogen
One of he elements of Group 7 of the periodic table (fluorine, chlorine, bromine, iodine, and astatine); halogens combine with most metals to form salts.
Alkali Metal
One of the elements in Group 1 of the periodic table (lithium, sodium, potassium, rubidium, cesium, and francium.
Noble Gas
One of the elements of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, and radon); noble gases are unreactive.
Alkaline-earth Metal
One of the elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, and radium)
Periodic Law
The law that states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of elements.
Atomic Mass
The mass of an atom expressed in atomic mass units.
Mass Number
The sum of the numbers of protons and neutrons in the nucleus of an atom.
Periodic
Describes something that occurs or repeats at regular intervals.
Period
In chemistry, a horizontal row of elements in the periodic table.
Nucleus
In physical science, an atom's central region, which is made up of protons and neutrons.