Atoms and Subatomic Particles: Quick Review

Matter

  • Definition: Anything that has mass and takes up space; exists as solid, liquid, or gas.

Mass

  • Definition: A measurement of how much matter is in an object; units: gg, kgkg.

Element

  • Definition: A pure substance that cannot be broken down into other substances.

Periodic Table

  • Definition: Arrangement of elements sorted by increasing atomic number; groups elements by properties.

Atom

  • Definition: The smallest particle of an element that still retains the properties of the element.

Subatomic Particle

  • Definition: Particles that make up atoms: protons, neutrons, and electrons.

Electron

  • Definition: Particle with charge −1-1; surrounds the nucleus.

Valence Electron

  • Definition: The electrons in the outermost shell, or energy level.

Electron Cloud

  • Definition: The area surrounding the nucleus where the electrons are most likely to be found.

Orbitals / Energy Level

  • Definition: The energy levels around the nucleus where electrons reside.

Neutron

  • Definition: Electrically neutral particle inside the nucleus.

Proton

  • Definition: Particle in the nucleus with charge +1+1.

Nucleus

  • Definition: The small, positively charged center of an atom; contains protons and neutrons.

Atomic Number

  • Definition: Number of protons in the nucleus; protons determine an atom's identity.

Atomic Mass

  • Definition: The decimal number used on the periodic table indicating the average mass of the nucleus.

Mass Number

  • Definition: Number of protons and neutrons in the nucleus; it is the atomic mass rounded to the whole number with no decimals.