How Atoms Differ

I. Properties of Subatomic Particles

Particle Symbol Location Relative

Charge

Relative mass

Actual mass (g)

Electrone- or In the space

surrounding the nucleus

1-1

1840

9.11

x 10-28

Protonp+ or

In the nucleus 1+ 1

1.673

x 10-24

Neutron

n0 or In the

nucleus 0 11.675

x 10-24

e01

p11

n10

II. Atomic Number• the number of protons in an atom• Identifies element – each atom has unique #– # never changes

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

•# of neutrons = mass number – atomic number

IV. Isotopes• Atoms of the same element but have a

different # of neutrons• Ex: 3 isotopes of carbon:

• All elements have isotopes (some 2, some 3, etc.)

• Some isotopes are naturally radioactive.• Ex: Plutonium

V. Representing Isotopes• In Ag-107, the 107 represents the mass number (neutrons + protons)• the 47 represents the number of protons

Practice:

1. What is the mass number for Co-59?2. What is the mass number for

597

VI. Atomic Mass•The standard is the atomic mass unit (amu): defined as 1/12 of the mass of a carbon-12 atom

•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

) + …

Practice 3• Silver 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 atomic mass of silver.

Practice 4

• Rubidium 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

Vocabulary to Know

• Atomic #- same # of protons & electrons• Mass #-protons + neutrons

written 2 ways: Carbon-14 or C• Isotopes-same # of protons, different # of

neutrons• Atomic mass-weighted average mass

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