Atomic Structure

An atom is the smallest unit of matter that will retain it's physical and chemical properties. Because of this we will not be talking about many of the particles that make up atoms. However we will focus on 3 subatomic particles (particles smaller than an atom): the proton, neutron, and electron.

Anatomy of an Atom

Protons

found in the nucleus (center) of the atom
have a positive charge (+1)
has a mass of 1 atomic mass unit (AMU)

Neutrons

found in the nucleus (center) of the atom
have no electrical charge (0)
has a mass of 1 atomic mass unit (AMU)

Electrons

found in orbitals outside of the nucleus of the atom
have a negative charge (-1)
The mass is so small compared to protons and neutrons that its mass is ignored.

Elemental symbols

Each type of atom is represented by an elemental symbol. For example, atoms with an atomic number of 11 are known as sodium and are represented by the symbol Na. Atoms can have either 1 letter or 2 letters in their atomic symbols. In either case the first letter of the atomic symbol is always capitalized. If there is a second letter it is always lowercase. Sometimes the atomic symbol is accompanied by a few numbers that represent different characteristics of the atom.

Atomic Number (Z number)

The atomic is determined by the number of protons. This is the most important characteristic of an atom. It determines the atoms chemical identity.

Atomic Mass (A number)

This is determined by the total number of protons and neutrons. Also sometimes called the atomic weight. This characterizes how much matter an atom has. Atomic mass is measured in atomic mass units (amu)

Charge (Q number)

The charge or electrical charge is determined by the number of protons minus the number of electrons. Protons have a positive charge and electrons have a negative charge. If there are more protons than electrons the atom will have a overall positive charge. If there are more electrons the atom will have a net negative charge. Atoms that have a charge are called ions.

Practice

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