Atomic Mass, Atomic Number, Ions and Isotopes

Atomic mass unit

(amu) A small mass unit used to describe the mass of very small particles such as atoms and subatomic particles

Atomic number

Number of protons in the nucleus of an atom

Average atomic mass (amu)

*The mass of a single atom

Net charge

How many protons and electrons "balance out"

Zero net charge

Atoms with an EQUAL number of protons and electrons

# Protons = # Electrons

Positive net charge

Atoms with more protons than electrons

# P > # E

Atoms with a positive charge are called: Cations

Negative net charge

Atoms with less protons than electrons

# P < # E

Atoms with a negative net charge are called: Anions

Ions

Atoms with a charge

Atoms become ions by gaining or losing electrons

Anion

Atoms that have GAINED electrons

Electrons have a NEGATIVE CHARGE. When an atom gains electrons, there are more electrons than protons

+1 charge

The atom (ion) has 1 MORE PROTON than electrons

-1 charge

The atom (ion) has 1 MORE ELECTRON than protons

+2 charge

The atom (ion) has 2 MORE PROTONS than electrons

-2 charge

The atom (ion) has 2 MORE ELECTRONS than protons

Cation

An atom that LOST electrons and therefore has a positive charge.

Neutral atom

Protons = Electrons

The number of protons and electrons are the SAME (equal) and the atom has NO CHARGE

Atom

smallest part of matter that still acts like the element it is

Isotope

Atoms of the same element that have different numbers of neutrons

Isotope notation example

Isotopes of Carbon