• smallest unit of an element
• maintains the properties of that element
• is made up of matter

• subatomic particle
• has a negative charge
• found outside the nucleus

• "brain of the atom"
• made up of protons & neutrons

a region (place) around the nucleus of an atom

• likely place to find electrons

• all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed
• Atoms of the same element are exactly alike, & atoms of different elements are different
• Atoms join with other atoms to make new substances

• nucleus (center of the atom)
• Protons (+ charge inside the nucleus)
• Neutrons (neutral - no charge inside the nucleus)
• Electrons (- charge outside the nucleus in the electron cloud)

• subatomic particles
• positive charge
• found in the nucleus of the atom

Atomic Mass Unit

(amu)

• Expresses the mass of an atom or particle
• Each proton has a mass of about 1 amu

• subatomic particle
• has no charge
• found in the nucleus of the atom

1. Protons
2. Neutrons

• a charged atom or molecule.
• It is charged because the number of electrons do not equal the number of protons in the atom or molecule.

• the number of protons (+ charge) in the nucleus of the atom
• all atoms of an element have the same atomic number

• have the same number of protons but have different numbers of neutrons

• Radioactivity - caused by an atom with a nucleus that will change over time
• radioactive atoms spontaneously fall apart after a certain amount of time
• when they fall apart they give off energy

• the mass of an atom expressed in atomic mass unit (amu)
• the number of protons & neutrons
• it's a weighted average of natural isotopes of an element