Unit 1: Matter and Atomic Structure

Atom

The smallest unit of matter. Has all the chemical properties of an element.

Proton

Subatomic particle with a mass of 1 amu and a charge of +1, located in the nucleus.

Neutron

Subatomic particle with a mass of 1 amu and a charge of 0 or neutral, located in the nucleus.

Electron

Subatomic particle with a mass of 0 amu and a charge of -1, located in the electron cloud.

Atomic Number

The number of protons in an atom, which determines the identity of the element.

Mass Number

The sum of the number of protons and the number of neutrons in an atom.

Average Atomic Mass

A weighted average of the different masses of each element.

Element Symbol

A one or two-letter abbreviation used to represent an element in the periodic table.

Hyphen Notation

The element is written as Element Name-Mass number, e.g., Carbon-13.

Nuclear Symbol

The element symbol is written with the mass number on the top and the atomic number on the bottom, e.g., 12/6 C.

Ion

Atoms that have a charge due to a different number of electrons than protons.

Cation

An atom that lost electrons, resulting in a positive charge.

Anion

An atom that gains electrons, resulting in a negative charge.

Matter

Anything that has mass and takes up space.

Pure Substance

Has a fixed composition and cannot be separated physically.

Element

A pure substance consisting of only one type of atom.

Compound

A pure substance formed from two or more elements that are chemically combined.

Mixture

Two or more pure substances mixed together that can be separated physically.

Homogeneous Mixture

A mixture that appears uniform throughout.

Heterogeneous Mixture

A mixture that does not appear uniform and where the differences can be seen.

Electron Shells/Rings

Regions around the nucleus where electrons are likely to be found.