How Atoms Differ

a. Properties of Subatomic ParticlesParticle Symbol Location Relative

Charge

Relative mass

Actual mass (g)

Electron

Proton

Neutron

b. Atomic Number• the number of protons in an atom• Identifies element

c. Mass Number•represents the total number of protons and neutrons in the nucleus

AZatomic number

XMass number

d. Isotopes• Atoms that have the same number of protons

but have a different masses• Ex: 3 isotopes of carbon:

126C 136C 146C

e. Average Atomic Mass• the weighted average of the isotopes of that element.• Formula:

Atomic mass of

an element= (

% abundance

ofIsotope #1

x

massof

Isotope #1

) + (

% abundance

ofIsotope #2

xmass

ofIsotope #2

) + …

Example 1Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of 106.9 amu. Ag-109 has a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the average atomic mass of silver.

Example 2Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?

8537

8737

Example 3Boron has two naturally occurring isotopes. If the abundance of 11B is 80.10% with an amu of 11.0093, find the abundance of 10B.