Ions & Compounds

Ions• atoms that have lost or gained electrons• do this to get a stable outer shell (8)• they now have a charge

Example 1

Lithium Atom

• Li• 3 protons• 3 electrons

Example 1

Lithium Atom

• Li• 3 protons• 3 electrons

Lithium Ion

• Li+

• 3 protons• 2 electrons

Example 2

Calcium Atom

• Ca• 20 protons• 20 electrons

Example 2

Calcium Atom

• Ca• 20 protons• 20 electrons

Calcium Ion

• Ca2+

• 20 protons• 18 electrons

• As you can see from the two examples, metals tend to have 1, 2, or 3 valence electrons

• When they combine with other elements, they tend to lose these electrons

Example 3

Fluorine Atom

• F• 9 protons• 9 electrons

Example 3

Fluorine Atom

• F• 9 protons• 9 electrons

Fluoride Ion

• F-

• 9 protons• 10 electrons

Example 4

Sulfur Atom

• S• 16 protons• 16 electrons

Example 4

Sulfur Atom

• S• 16 protons• 16 electrons

Sulfide Ion

• S2-

• 16 protons• 18 electrons

• As you can see from the last two examples, nonmetals tend to have 5, 6, or 7 valence electrons

• As you can see from the last two examples, nonmetals tend to have 5, 6, or 7 valence electrons

• When they combine with other elements, they tend to gain electrons

• As you can see from the last two examples, nonmetals tend to have 5, 6, or 7 valence electrons

• When they combine with other elements, they tend to gain electrons

• Naming nonmetal ions – ending changes to “ide”

Cations vs. Anions

• Cations are atoms that have lost an electron to become positively charged

Cations vs. Anions

• Cations are atoms that have lost an electron to become positively charged

Calcium Ion = Ca2+

Cations vs. Anions

• Anions are atoms that have gained an electron to become negatively charged

Cations vs. Anions

• Anions are atoms that have gained an electron to become negatively charged

Fluoride Ion = F-

IONIC COMPOUNDS

• atoms combine with other atoms to form compounds and fill their outer shell

• this makes them stable• one is now a cation and other an anion• opposite charges so are ATTRACTED to each

other (ionic bond)• stay together• stable compound

Properties of Ionic Compounds

• strong bond between + and – charged ions• crystalline-shaped compound, so is hard and

brittle• high melting point (needs a lot of energy to

break the bonds)• conducts electricity when dissolved in water

(doesn’t conduct in a solid state)• Most are soluble in water (except CaCO3)

Writing Formulas for Ionic CompoundsZero Sum Rule:•sum of the charges must equal zero•total # of + charges + total # of - charges•ex Mg + Cl1.Write symbols, metal first

Mg Cl2.Write the charge above the symbol

+2 -1

Mg Cl

3. Determine how many of each ion are needed to bring total charge to zero

1 (+2) + 2 (-1) = 0

Mg Cl4. Write the chemical formula using the

coefficients (red) as subscripts.Mg1 Cl2

5. Don’t write subscript 1Mg Cl2

Find the formula for aluminum and oxygen

Crisscross Method• a shortcut method• eg calcium and flourine1.Write the symbols and their charges

2+ 1-

Ca Cl2. Crisscross the charges above so they now become coefficients

Ca Cl2

• use the crisscross to find the formula for magnesium and oxygen

Naming Ionic Compounds

• the metal always goes 1st, non-metal 2nd

• non-metal’s ending changes to ‘ide’• ex sodium + chlorine sodium chloride• name the other ionic compounds you’ve

written the formula for

Multiple Ionic Charges• some metals can form more than one ion

(multivalent)• ex. iron can be Fe2+ or Fe3+

Naming Multivalent Compounds

• must include the ionic charge of the compound in the name

• comes after the metal, written in Roman Numerals (I, II, III, IV, V)

• ex. FeCl2

Iron (II) Chloride• whenever writing chemical name of a compound

check to see if it has more than one charge

Polyatomic Ions

• stable gp of several atoms acting together as a single ion

• don’t break apart• together have an overall charge• ex. phosphate PO4

3-