1. Atoms, Ions, and Isotopes

2. Quick Review Atoms are made up of three particles:
Protons
Neutrons
Electrons
Question: Which of the three particles identifies what element an atom is?
The PROTON! (very important)

3. Different Forms of the Same Element
In any element, the # of protons is always constant.
Unlike the number of protons, the number of electrons and neutrons can vary within an element without changing the identity of the element.
Ex. Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-8 neutrons and 2-10 electrons

4. Isotopes The # of protons does NOT change!
An ISOTOPE is a form of an element that has a different number of neutrons than “normal”
The # of protons does NOT change!
Ex:
The most abundant Carbon has 6 protons, electrons and neutrons
So the atomic number is 12
There is also Carbon 14 which still has 6 protons and electrons, but 8 neutrons
The atomic mass is now 14 because of the extra neutrons

5. Other Isotopes Most atoms have naturally occurring isotopes including:
Radon
Potassium
Uranium
When an element is “radioactive” it means it has an unstable number of neutrons (an unstable ISOTOPE)

6. IONS
An atom usually has a neutral charge. That means it has the same number of protons as electrons
Remember, a proton has a positive charge and an electron has a negative charge
ION – an atom that has lost or gained one or more electrons and has become charged either positively or negatively

8. Positive Ions When an atom LOSES electrons, it becomes more POSITIVE
Why?
If you are getting rid of negative particles (electrons) but your number of positive particles (protons) are staying the same.
In other words, you are subtracting negative numbers

9. Examples What would the charge be if:
The neutral form of Gold (Au) lost 4 of its 79 electrons. It now has 79 protons and 75 electrons
The neutral form of Mg lost 2 of its 12 electrons. It now has 12 protons and 10 electrons.

10. Negative Ions When an atom GAINS electrons it becomes more NEGATIVE
Why?
Electrons have a negative charge, so the more you have, the more negative you become

11. Representing Ions
Ions are represented by placing a “superscript” charge number next to the atomic symbol.
Ex.
O-2 = oxygen with a negative 2 charge
K+ = potassium with a positive 1 charge
N-3 = nitrogen with a negative 3 charge
And so on