Atomic Number- the number of protons in the nucleus of an atom of that element

Ex: Hydrogen atoms have only one proton in the nucleus, so the atomic number is 1.

Atoms are neutral, so the # of protons =# of electrons.

Total number of protons and neutrons in an atom.

Mass = # protons + # neutrons The # of neutrons in an atom is the

difference between mass # and atomic #. # Neutrons = Mass # - Atomic #

Atoms that have the same # of protons, but different # of neutrons.

If they have more/less neutrons, then the mass number will be different!

Have same number of protons and electrons. Only difference is # of neutrons!

A way to measure the mass of an atom, using a standard (carbon-12).

Carbon-12 has 6 protons and 6 neutrons. It’s mass is set at 12 amu. So the mass of a single proton or neutron is about 1 amu.

Atomic Mass- weighted average mass of the atoms in a naturally occurring sample of the element.

Ca

P-3

Al+3

1. Change abundance percents into decimals.

2. Multiply the mass of each isotope by its natural abundance. (expressed as decimal)

3. Add the products.

Element X has two natural isotopes. The isotope with a mass of 10.012 amu has a relative abundance of 19.91%. The isotope with a mass of 11.009 amu has a relative abundance of 80.09%. Calculate the atomic mass and identify this element.

The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass = 62.93 amu, and 30.8% for mass = 64.93 amu. Calculate the average atomic mass of copper.

Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).