IONS

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?

ANSWERIf an element is neutral (does

not have a charge), then the element has the same number of electrons and protonsAll of the (+) from the

protons is cancelled out by the same number of (-) from the electrons

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

VOCABULARY DISTINCTION

If an element has the same number of protons and electrons (neutral), it is called an atom

If an element has a different number of protons and electrons (has a charge), it is called an ion

IONSAtoms start of with a neutral charge In other words, they have the same

number of e- and protonsExample: Oxygen (O) has an atomic

number of 8This means it has 8 protonsTherefore a neutral oxygen atom

also has 8 e-

IONSWhen an atom gains or loses

electrons the atom forms a chargeExample: Neutral oxygen (O) atom

has 8 protons and 8 electrons In a chemical reaction, O gains 2

electrons8 protons (+) and 10 electrons (-)

gives a net (-2) charge

IONS Formula for calculating ion charge:

#protons - #electrons = ion charge

How do we show an ion using a symbol? Neutral atom is the normal atomic

symbolFor example: Neutral oxygen = O

An ion shows the charge associated with the atomFor example: Oxygen with a -2 charge

= O-2

IONS Calculate the charge on the following ions

and write out the ion symbol:1. Chlorine (Cl) atom with 18 electrons2. Aluminum (Al) atom with 10 electrons3. Copper (Cu) atom with 27 electrons4. Potassium (K) atom with 18 electrons5. Sulfur (S) atom with 18 electrons

IONS Answers:

1. Cl-

2. Al+3

3. Cu+2

4. K+

5. S-2

NOTE: When an ion has a (+1) or a (-1) charge, we only write a (+) or a (-)

ION TYPES Definition of ions

Cation: an ion that has a positive charge

Anions: an ion that has a negative charge

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

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 7 (halogens): gain 1 e- to form (-1) charge

Group 16: gain 2 e- to form (-2) chargeGroup 15: gain 3 e- to form (-3) chargeTransition metals: lose different

amounts of e-

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

EXAMPLEHow would you write the symbol for

an atom that has 29 protons, 34 neutrons and 27 electrons?

Step 1: Find the symbolStep 2: Number of protons goes in

the bottom leftStep 3: Protons + neutrons goes in

the upper leftStep 4: Charge (protons – electrons)

go in the upper right

ANSWER

Cu63

29

+2

TRY THESE1. An atom with 35 protons, 45

neutrons, and 36 electrons.2. An atom with 12 protons, 13

protons, and 10 electrons.3. An atom with 10 protons, 10

neutrons and 10 electrons.

TRY THESE Write down the number of protons,

neutrons and electrons for the following:

32S-2

16

56Fe+3

26

39K+

19