Notes on Isotopes

• Remember Protons are (+) and Electrons are (-).

• Neutrons were the last sub-atomic particles to be discovered because they have no electrical charge.

• All atoms of an element have the same number of protons. (Atomic #)

• The number of neutrons can vary from one atom of an element to another.–These variations are called ISOTOPES.

• Isotopes are atoms of the same element that have different masses because they have different numbers of neutrons.

–Protons and Neutrons have about the same mass.

–Electrons have so little mass they don’t affect the atom’s mass.

• Mass number tells us how many protons and neutrons are in the nucleus of an atom.–It is always a whole number.

Isotope Notation

• 2 Forms:

Carbon-12 (12 is the mass number)

• Carbon will always have 6 protons

How many neutrons does Carbon-14 have?

there are 14 total protons and neutrons.6 of them are protons.So 14 (total) – 6 (protons) = 8 Neutrons

How many neutrons does Carbon-12 have?

• Atomic Mass (atomic weight) is the average mass of all of the known stable isotopes of an element.– Most have decimals because they are

averages.– This is the # on the periodic table

• Mass Number is specific to an isotope.– Not written on periodic table– Rounding the atomic mass usually gives you

the most common mass number.