Full transcript
0:07You can learn a lot about the physical properties of an element
0:10by reviewing the periodic table. Let’s take a look at carbon
0:14as an example.
0:17The number that appears above the element’s symbol is called the atomic number.
0:21The atomic number tells you the number of protons that are in the nucleus
0:25of an atom. So in the case of carbon, you can see that it
0:29has 6 protons in its nucleus.
0:33In an atom of carbon that is neutral, there must also be 6 electrons.
0:37This is because the positive charge of carbon’s protons must
0:41be balanced by the negative charge of carbon’s electrons.
0:45Because electrons and protons have an equal and opposite charge,
0:49there must be an equal number of both protons and electrons
0:53in a neutral atom of an element. The number that
0:57appears below the element’s symbol is called the atomic mass.
1:01The mass of an atom depends on the number of protons, neutrons and
1:05electrons it contains. However, since electrons
1:09are so small, their mass is assumed to be zero in most calculations.
1:14Therefore,
1:15the atomic mass of an atomic is equal to the sum of its protons
1:19and neutrons. However, you’ll notice that carbon has an atomic
1:23mass of 12.01. This is because the number
1:27associated with the atomic mass on the periodic table, is
1:31equal to the average of its naturally occurring isotopes.
1:34All of the isotopes of carbon vary slightly in their atomic mass.
1:38When we average these together,
1:41we get 12.01. If you know the
1:45atomic number and atomic mass, you can determine the number of neutrons
1:49in an element. Simply subtract the atomic number,
1:53or the number of protons, from the atomic mass,
1:57the number of protons plus neutrons, and take the closest whole
2:01number. So 12.01
2:05minus 6 equals 6.01, which
2:09rounds to 6. So the number of neutrons in a neutral atom
2:13of carbon, is 6.