CHM1045 Chapter 2

Atomic Theory

An atom consists of a nucleus (protons and neutrons) surrounded by electrons. The electron’s motion around the nucleus give the atom most of its volume.

What is a neutron?

A neutron is a subatomic particle found in the nucleus of an atom. It has no electric charge and a mass slightly greater than that of a proton. Mass of about 1 amu

What is a proton?

A proton is a subatomic particle found in the nucleus of an atom. It has a positive electric charge and is a key component in determining an element's atomic number. Mass of about 1 amu

What is an electron?

An electron is a subatomic particle that orbits the nucleus of an atom. It has a negative electric charge and a very small mass compared to protons and neutrons.

Atomic Symbol

Abbreviated version of element. Ex: Be

Mass Number

The total of all the atom’s nuclear particles (neutrons+protons). Shown in top left corner left to atomic symbol

Atomic Number

The number of protons in the atom’s nucleus. Defines the element, and is how the periodic table is set up.

Isotope

An element has the same number of protons, but a different number of protons. Atomic mass will be different but isotopes behave the same chemically.

Monatomic Ions

Single atoms that have lost or gained electrons- becoming positively or negatively charged

Cations

Lost electrons and are positively charged

Anions

Have gained electrons and are negatively charged

Atomic Mass

The average mass of all an element’s stable isotopes, weighted by percent abundance. Shown below atomic symbol on periodic table

Percent Abundance

Tells how commonly an isotope is found in comparison to the others. Decimals should add up to 1.