ReviewParticle Symbol Charge Mass

(amu)Location

Electron e- -1 About 0.000544

Surrounding nucleus

Proton p+ +1 About 1 Inside nucleus

Neutron n0 0 About 1 Inside nucleus

IsotopesJ.J. Thomson saw that there were two different neon atoms in the cathode ray tube

These atoms were different in mass, but the same chemically

Atoms of the same element that have a different mass are known as Isotopes

IsotopesContain the same number of protons

Contain a different number of neutrons

Two definitions for isotopes:Atoms of the same element with different amount of neutrons

Atoms of the same element with difference in mass

Isotope UsesCarbon dating

Can determine the amount of carbon-14 in a sample to find the age of rock

Smoke DetectorsWhen smoke is present, conductivity in detector changes from small amount of radioactive material

Cancer treatmentsRadiopharmaceuticals

Henry Moseley

Henry MoseleyFound that the wavelength of X-rays depended on the number of protons in the nucleus of the atom

Also found that the number of protons is always the same in an element

Atomic number: number of protons in an element

Protons: positive charge, mass: about 1 amu, symbol p+

Looking at the Numbers

Nucleons: particles that make up the atomic nucleus

Mass Number: the total number of nucleons (protons and neutrons) in an atom

Neutrons: neutral charge, mass: about 1 amu, symbol n0

If you know this, you can figure out the number of protons, neutrons, and the mass number of anything!

Writing Isotopes There are two main ways that isotopes can be written for an element.

126I Hydrogen-3Isotopes of Neon

Neon-20: 10 neutrons

Neon-21: 11 neutrons

Neon-22: 12 neutrons

Atoms are NeutralThe number of protons must equal the number of electrons for the atom to be neutral

Isotopes change the number of neutrons

Let’s Practice!An atom of vanadium contains 23 electrons. How many protons does it contain?

An atom of silver contains 47 protons. What is its atomic number?

How many electrons, neutrons, and protons are found in a copper atom of mass number 65?

Atomic MassOn the periodic table, the AVERAGE atomic mass is given at the bottom

This number represents the average mass of all of the isotopes for that particular element

This number also involves the abundance of these particular isotopes in nature.

Atomic Mass Calculations

Calculate the average atomic mass of gold with 50% of gold being gold-197 and 50% being gold-198.

Element Symbol Atomic Number

# Electrons

# Neutrons

Mass Number

Helium 2 2

Ti 22 50

73 108

Nickel 28 39

Gallium 31 65

83 83

Bh 107 200