Science: Atoms

Electron

A negatively charged particle that moves around the nucleus The mass of an electron is less than one thousandth of the mass of a proton

Neutron

A particle with no charge located in the nucleus of an atom. Neutrons have slightly more mass than protons. The number of neutrons is described by the neutron number, N. To find the number of neutrons, subtract the atomic number from the mass number.

Energy Level

A particular region where electrons can orbit a nucleus

Proton

A positively charged particle located in the nucleus of an atom. Protons have slightly less mass than neutrons The number of protons determines the element

Element

A pure substance that cannot be broken down into simpler substances by ordinary chemical means Elements are mad of one type of atom Atoms of different elements are distinguished by the number of protons in the nucleus. For example, all carbon atoms have 6 protons.

Radioactive

Capable of releasing radiation In a radioactive atom, the nucleus can spontaneously decay and emit particles and/or light. These emissions are called radiation. The energy released by radioactive substances can be harnessed to produce electricity in a nuclear power plant. This energy also can be used to create a massive explosion in a nuclear bomb. If the emissions change the number of protons in the nucleus, the atom becomes a different element.

Valence electrons

Electrons found in the outermost energy level of an atom.

Atomic Number

The number of protons in the nucleus of an atom. Elements are distinguished from one another by their atomic numbers. For example any atom with two protons is an atom of helium The symbol for the atomic number is Z In an element symbol, the atomic number is shown at lower left.

Nucleus

The positively charged, dense center of an atom. The nucleus contains protons and neutrons,

Periodic table

a chart that organizes the chemical elements based on their properties

Electron dot diagram

a diagram that shows the element symbol surrounded by dots representing valence electrons For example, the electron dot diagram at right shows that neutral helium atoms have two valence electrons.

Ion

an atom that has an electrical charge because it has gained or lost electrons. An atom with more protons than electrons is a positively charged ion or cation An atom with more electrons than protons is a negatively charged ion, or anion In an element symbol, the electric charge is shown at upper right

Isotope

one of several forms of the same element. All isotopes of a given element have the same number of protons, but differ in the number of neutrons. Most isotopes are radioactive. Usually only one or two stable isotopes exist for a given element

Atom

the basic unit of matter An atom is the smallest particle of an element that still has all the properties of the element. Atoms are made up of smaller particles called protons, neutrons, and electrons. The smaller electrons orbit around a central nucleus of protons and neutrons.

Mass Number

the number of protons plus neutrons in the nucleus of an atom for example, the mass number of helium is 4 (2 protons and 2 neutrons). The symbol for the mass number is A. In an element symbol, the mass number is shown at upper left.