1. Exceptions to the Rule…
For each given element, the number of protons is ALWAYS the same
If you change the number of protons, you are now working with a different element
Each element can have a different number of neutrons or a different number of electrons, but it will still be the same element
A different number of electrons is called an ion
A different number of neutrons is called an isotope

2. Isotopes
If the number of neutrons is different, it will have a different atomic mass number
For example carbon can have a mass of 12 (usually) or 13 (rarely, but still exists)
Hydrogen has three isotopes, Hydrogen 1 (called Hydrogen), Hydrogen 2 (Deuterium), or Hydrogen 3 (Tritium)

3. Here are three isotopes of an element:
612C 613C C
The element is: __________________
The number 6 refers to the _________________________
The numbers 12, 13, and 14 refer to the ________________________
How many protons and neutrons are in the first isotope? _________________
How many protons and neutrons are in the second isotope? _________________
How many protons and neutrons are in the third isotope? _________________

4. 92 uranium-235 92 uranium-238 5 boron-10 5 boron-11 Isotope name
atomic #
mass #
# of protons
# of neutrons
# of electrons
92 uranium-235
92 uranium-238
5 boron-10
5 boron-11

5. ASSESSMENT TIME! Elements – names / symbols Classifying Matter - Pure Substances / Mixtures Atomic Structure – Protons, Neutrons, Electrons, neutral atoms,

6. Ions
When an element has no charge, its number of protons (positive) is equal to its number of electrons (negative)
When it has a charge, called an Ion, it has a different number of electrons (remember, the number of protons can not change)
Fluorine, neutral is 9 protons and 9 electrons
Fluoride ion, -1 charge is 9 protons and 10 electrons
Sodium, neutral is 11 protons and 11 electrons
Sodium ion, +1 is 11 protons and 10 electrons