Chemistry Test Study guide

Explain what an atom is.
The smallest particle of an element.


Identify what particles of an atom are composed of.

Particles of an atom are made of protons, neutrons, and electrons. 
Identify particle charge and location.

Protons- positive charge- nucleus 

Neutrons- no charge- nucleus

Electrons- negative charge- outside of nucleus

Explain what the atomic number of an atom represents.
The atomic number is the number of protons in an atom.
Explain what the atomic mass of an atom represents.
The count of the number of particles in an atom’s nucleus.
How is the number of neutrons in an atom identified?
To find the number of neutrons in an atom subtract the atomic number from the atomic mass.
Describe what an electron shell is.

An electron shell is the “orbit” electrons follow around an atom’s nucleus.

Each shell can only hold a fixed amount.

Each shell must be filled before electrons fill the next shell.

Identify the maximum number of electrons found in each shell.


Distinguish between a group and a period.

A group goes in vertical columns and the elements have similar but not identical characteristics.

A period goes in horizontal rows, elements in a period are not alike in properties.

Describe what valence electrons are.
Valence electrons are electrons that are farthest away from the nucleus of an atom and involved in chemical reactions.