Ions

An ion is a charged atom. That means that the number of protons does not equal the number of electrons, as it does in a neutral atom

Remember the charges of subatomic particles:

To calculate charge:

charge = # of protons – # electrons

Example: If an atom of fluorine(atomic # 9) has 10 electrons, its charge is 9 - 10 = -1

Ions are chemically different from their neutral counterparts. Example: F - (fluoride: in naming negative ions, we

change the suffix of the neutral element's name to ide.) can be used in toothpaste to prevent cavities.

F (fluorine) however, is extremely poisonous. In fact it is the most poisonous gas of the

periodic table.

Characteristics of ions

Negative ion

# of electrons > # of protons

Overall charge is negative

Positive ion

# of electrons < # of protons

Overall charge is positive

Rutherford-Bohr model

Protons are located in the nucleus (center)

Electrons orbit the shells

Lewis notation

The Lewis notation is a simplified representation of the atom where only the valence electrons are illustrated (using dots)

Gaining/Losing electrons

The octet rule says that atoms tend to gain, lose or share electrons so as to have eight electrons in their outer electron shell

They all want to be like the noble(inert) gases (who have 8 valence electrons) so they will either gain or lose electrons to accomplish this task

***Remember valence electrons are the number of electrons in the outermost shell***

Tendency to gain/lose electrons for the elements in Group AFamily

number

IA II A III A IV A V A VI A VII A VIII A

Example of element

Li Be B C N O F Ne

Number of valence electrons

1 2 3 4 5 6 7 8

Tendency

Lose 1 electron

Lose 2 electrons

Lose 3electrons

Gain or lose 4 electrons

Gain 3 electrons

Gain 2 electrons

Gain 1 electron

Nothing

MOLECULE

Definition:

A molecule is the combination of two or more atoms that are chemically bonded together

Solutions

A solution is a homogeneous mixture (1 phase) where we can’t distinguish the substances that compose it even with the aid of observation instruments

Aqueous solution

An aqueous solution is a solution where the solvent is water

Concentration

The concentration of a solution corresponds to the quantity of solute over the quantity of solution

Dilution/Dissolution

Dilution : add solvent to the solution

Dilution = decrease in concentration

Dissolution: add solute to the solution

Dissolution = increase in concentration

Ways of expressing concentration

In number of grams of solute per litre of solution (g/L)

In number of grams of solute per 100 ml of solution ( % m/v )

In number of millilitres of solute per 100 ml of solution ( % v/v)

In number of grams of solute per 100 g of solution ( % m/m)

Calculating ConcentrationTo calculate concentration in g/L we can

usethis formula

C = m V

C (concentration g/L) m ( mass in g) V (volume in L)

Concentration in ppm

Concentration in ppm corresponds to the number of parts of solute dissolved in one million parts of solution

1 ppm = 1 g = 1 mg = 1 mg/kg

1 000 000 g 1000 g

In aqueous solutions:

1 ppm = 1 g = 1 mg/L 1000L

Questions

1. What are 2 ways that we can change the concentration of a solution?

2. Which of the following is most concentrated?

A. 24 g solute in 150 ml solutionB. 21 g solute in 125 ml solutionC. 32 g solute in 250 ml solution

__________ __________ _________Most least

Questions

3. Fill in the table