Science 3-1 3-2

Energy Level

a region of an atom in which electrons of the same energy are likely to be found

Mass Number

the sum of neutrons and protons in an atomic nucleus

Periodic Table

An arrangement of the elements showing the repeating pattern of their properties

Isotope

An atom with the same number of protons and a different number of neutrons from other atoms of the same element.

Group

Elements in the same vertical column of the periodic table; also called family

Proton

Small, positively charged particles that are found in the nucleus of an atom

Atomic Mass

The average mass of all the isotopes of an element

Atom

The basic particle from which all elements are made; the smallest particle of an element that has the properties of that element

Atomic Number

The number of protons in the nucleus of an atom

Electron

A tiny, negatively charged particle that moves around the nucleus of an atom

Nucleus

1. In cells, a large oval organelle that contains the cell's genetic material in the form of DNA and controls many of the cell's activities. 2. The central core of an atom which contains protons and neutrons. 3. The solid core of a comet.

Period

A horizontal row of elements in the periodic table

Chemical Symbol

A one or two letter representation of an element

Neutron

A small particle in the nucleus of the atom, with no electrical charge