1. IONS

2. SO FAR . . .
So far we’ve discussed how to find the number of protons and neutrons in an element.
How many electrons do we have in an element?
WHAT DO YOU THINK?

3. ANSWER
If an element is neutral (does not have a charge), then the element has the same number of electrons and protons
All elements on the Periodic Table are neutral
All of the (+) from the protons is cancelled out by the same number of (-) from the electrons

4. IONS
In chemical reactions, atoms often gain or lose electrons (e-) to form charged particles
IONS: an atom or group of atoms that has an electric charge because it has lost or gained electrons
NOTE: From now on, I will abbreviate (e-) for electrons

5. VOCABULARY DISTINCTION
If an element has the same number of protons and electrons (neutral), it is called an atom
atom=neutral
If an element has a different number of protons and electrons (has a charge), it is called an ion
Ion= have a charge

6. IONS Atoms start of with a neutral charge
In other words, they have the same number of e- and protons
Example: Oxygen (O) has an atomic number of 8
This means it has 8 protons
Therefore a neutral oxygen atom also has 8 e-

7. IONS When an atom gains or loses electrons the atom forms a charge
Example: Neutral oxygen (O) atom has 8 protons and 8 electrons
In a chemical reaction, O gains 2 electrons
8 protons (+) and 10 electrons (-) gives a net (-2) charge

8. IONS Formula for calculating ion charge:
#protons - #electrons = ion charge
8-10=-2
How do we show an ion using a symbol?
Neutral atom is the normal atomic symbol
For example: Neutral oxygen = O
An ion shows the charge associated with the atom
For example: Oxygen with a -2 charge = O-2

9. IONS
Calculate the charge on the following ions and write out the ion symbol:
Chlorine (Cl) atom with 18 electrons
Aluminum (Al) atom with 10 electrons
Copper (Cu) atom with 27 electrons
Potassium (K) atom with 18 electrons
Sulfur (S) atom with 18 electrons

10. IONS
Answers:
Cl-
Al+3
Cu+2 K+
S-2
NOTE: When an ion has a (+1) or a (-1) charge, we only write a (+) or a (-)

11. ION TYPES Cation: an ion that has a positive charge
Definition of ions
Cation: an ion that has a positive charge
Anions: an ion that has a negative charge

12. IONS
Ions behave differently than the atoms from which they are formed.
Na (neutral sodium)  very reactive and will explode in pure water
Na+ (sodium ion)  very stable (is in the table salt we eat)
Cations and anions combine together to form neutral compounds

13. AGAIN, LOOK AT YOUR PERIODIC TABLES
Group 1 (alkali metals): lose 1 e- to form (+1) charge
Group 2 (alkali earth metals): lose 2 e- to form (+2) charge
Group 15 (7A) (halogens): gain 1 e- to form (-1) charge
Group 16: gain 2 e- to form (-2) charge
Group 15: gain 3 e- to form (-3) charge
Transition metals: lose different amounts of e-

14. HOW DO WE COMBINE THE SYMBOLS FOR IONS AND ISOTOPES
Previously, we looked at how to show the symbol for atoms that have a certain number of protons and neutrons
Today, we will combine this with the number of electrons also

15. EXAMPLE
How would you write the symbol for an atom that has 29 protons, 34 neutrons and 27 electrons?
Step 1: Find the symbol
Step 2: Number of protons goes in the bottom left
Step 3: Protons + neutrons goes in the upper left
Step 4: Charge (protons – electrons) go in the upper right

16. ANSWER Cu +2 63 29

17. TRY THESE An atom with 35 protons, 45 neutrons, and 36 electrons.
An atom with 12 protons, 13 protons, and 10 electrons.
An atom with 10 protons, 10 neutrons and 10 electrons.

18. TRY THESES
Write down the number of protons, neutrons and electrons for the following:
32S-2 16
56Fe+3 26
39K+ 19

19. Fe+2 Roman Numerals When an element has a Roman Numeral after its name
Ex. Iron (II)
This is referring to its charge
Fe+2