Properties of ionic compounds

Standard chemObjectives 7

Properties of ionic compounds and relation to the ionic bond

Ionic compounds

Salts – ionic compoundsmetal + nonmetal or ion + ionEx. NaCl, MgO, K2S

Or NH4Cl, Ca3(PO4)2

take a look at the back of periodic table for list of common polyatomic ions and charges

What is the cause of the Properties of Ionic compounds?

• Strong forces of attraction between positive ions and negative ions make the ionic bond very strong

• Strong bonds leads to high melting and boiling points, so ionic compounds usually solids at room temperature

• Since an ionic compound is made up of ions (charged particles) it can conduct electricity when the ions are free to move – in aqueous solution or in molten state)

Properties of Ionic Compounds

- Do not consist of molecules – called formula units (there are no individual groupings of NaCl)

Crystal lattice• A regular pattern in which a crystal is arranged

The crystal lattice arrangement of sodium chloride

Properties of ionic compounds

Salts are hard and brittlehard – able to resist a large force applied to itbrittle – when the applied force becomes too strong to resist, the crystal develops a widespread fracture rather than a small dent

Brittle because of the positions of ions relative to each other

Draw diagram showing why salts are brittle

How to identify a compound as ionic1. All ionic substances are solid at room temperature (but

not all solids are ionic compounds)2. Tap substance gently – should not break apart easily, if it

breaks, should fracture into tinier crystals, not crumble into a powder

3. Heat substance – should have a high melting and boiling point

4. If it melts, check its conductivity – does it conduct electricity – ionic substance conduct electricity well when molten

5. Dissolve in water and check conductivity – ionic compounds conduct electricity when dissolved in water

Ionic CompoundsCrystalline solids (made of ions) High melting and boiling points Conduct electricity when melted Many soluble in water but not in nonpolar liquid

Covalent CompoundsGases, liquids, or solids (made of molecules) Low melting and boiling points Poor electrical conductors in all phases Many soluble in nonpolar liquids but not in water

1. The energy released when a salt is formed from gaseous ions is called thea. bond energy. b. potential energy. c. lattice energy. d. energy of crystallization. 2. The lattice energy is a measure of thea. strength of an ionic bond. b. strength of a metallic bond. c. strength of a covalent bond. d. number of ions in a crystal. 3. When an electron is added to an atom,a. an input of energy is required. b. energy is usually released. c. a stable octet is always formed. d. ionic bonds are broken. 4. Which of the following is NOT a property of an ionic compound?a. low boiling point b. brittleness c. hardness d. molten compound conducts electricity

5. Compared with ionic compounds, molecular compoundsa. have higher boiling points. b. are brittle. c. have lower melting points. d. are harder. 6. Because ions are more strongly attracted in an ionic compound

than molecules are attracted in molecular compounds, the melting points of ionic compounds are

a. equal for all ionic compounds. b. lower than the melting points of molecular compounds.c. higher than the melting points of molecular compounds.d. approximately equal to room temperature. 7. In a crystal of an ionic compound, each cation is surrounded bya. molecules. b. positive ions. c. dipoles. d. anions.

Summarize the following

List 4 properties of ionic compoundsExplain with a diagram why ionic compounds

are brittleWhat has to move in order to get an electric

current?