All atoms of a particular element have the
same atomic number; this means that they all
have the same number of protons.
But sometimes you can find heavy atoms of
a particular element. These atoms have a higher
mass number.
The mass number is equal to the number of
protons plus the number of neutrons, and we
can ignore the electrons as their mass is
so tiny.
If the number of protons always stays the
same in a particular element, and we are ignoring
the mass of electrons it must mean the number
of neutrons is causing this difference in
mass.
Atoms of the same element with a different
mass number are known as ISOTOPES.
They are defined as:
Atoms of an element which have the SAME number
of PROTONS, but a DIFFERENT number of NEUTRONS
If we look at Carbon and Nitrogen, are they
isotopes? They have different mass numbers.
BUT they also have different numbers of protons
therefore they are not isotopes, they are
completely different elements.
Different isotopes of elements do not have
separate positions on the periodic table.
They occupy the same spot because they have
the same number of protons.
What about Carbon-12 and Carbon-14?
Both Carbon-12 and Carbon-14 have the same
atomic number, which means they have the same
number of protons, but they have different
masses.
Carbon 12 has a mass of 12, and 6 protons.
REMEMBER: mass number = protons + neutrons
So we can rearrange this formula to give us:
neutrons = mass number - protons
12 -- 6 = 6 therefore it has 6 neutrons
Carbon 14 has a mass of 14, but it still only
has 6 protons.
Mass number = protons + neutrons. Rearrange:
neutrons = mass number - protons
14-6 = 8 therefore Carbon 14 has 8 neutrons.
Carbon-12 and Carbon-14 are not the only examples
of isotopes. There are many more, such as
Hydrogen, Deuterium, and Tritium, and Chlorine-35
and Chlorine-37.
Isotopes only differ in their number of neutrons
and their mass, their chemical properties
are exactly the same because neutrons have
no effect on elements chemical behavior. This
is controlled by electrons which we will discuss
in another video.
So, Isotopes are atoms of the same element
with the SAME number of Protons, but a DIFFERENT
number of NEUTRONS.
They have different masses, but their chemical
properties are exactly the same.
