Review
Particle
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
Isotopes
J.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
Isotopes
Contain 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 Uses
Carbon dating
Can determine the amount of carbon-14 in a sample to
find the age of rock
Smoke Detectors
When smoke is present, conductivity in detector
changes from small amount of radioactive material
Cancer treatments
Radiopharmaceuticals
Henry Moseley
Henry Moseley
Found 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-3
Isotopes of Neon
Neon-20: 10 neutrons
Neon-21: 11 neutrons
Neon-22: 12 neutrons
Atoms are Neutral
The 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 Mass
On 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
Helium
Ti
#
Electrons
# Neutrons Mass
Number
2
2
22
73
Nickel
108
28
Gallium
50
39
31
65
83
Bh
83
107
200