Mixtures and Compounds

Objectives: Describe the characteristics of mixtures

18-1 Mixtures

A mixture is formed when any two elements or compounds are blended together.

These blended materials touch each other but are not chemically combined, so a mixture can be physically separated. Dirt – a mixture of clay, sand, particles or dead

plants, and water. Cake and pancake mixes are other familiar

mixtures.

Mixture

Objectives: Identify the properties of solutions Distinguish between solute and solvent Compare the type of solutions Describe suspensions

18-2 Solutions

Liquid mixtures such as sugar dissolving in water are called solutions

Solutions have two parts: Solvent – is the part that dissolves another

material Solute – is the material that is dissolves

For example in the sugar water, water is the solvent and sugar is the solute.

Solutions

When a small amount of solute is dissolved in a solvent, the solution is called a dilute solution.

If a large amount of solute is dissolved in the solvent, the solution is said to be a concentrated solution.

When a solvent has dissolved all the solute it can at its present temperature, it is called saturated.

Heating and then cooling a solution to dissolve more solvent is called supersaturated solution.

Solutions

Gases and liquids can all be solvents and solutes. The air we breathe is a solution of nitrogen and

oxygen with other gases dissolved in them Carbon dioxide gas is dissolved in water to make

carbonated drinks, when you open the bottle the carbon dioxide bubbles out of the solution.

Metal alloys are solid solutions made by melting and mixing two of more metals

A suspension is a special type of solution that forms when a solvent cannot actually dissolve the solute because the molecules of the solute are larger than the molecules of the solvent.

Solutions

Objectives Distinguish between compounds and mixtures Identify common compounds and their

formulas Distinguish between organic and inorganic

compounds

18-3 Compounds

Compounds occur when two or more different kinds of atoms combine chemically.

Water is composed of two atoms of hydrogen and one atom of oxygen.

Compounds have physical and chemical properties that are different from the properties of the elements from which they are made.

Compounds

Compounds are written as chemical formulas, using the symbols of the elements that combine to make the compound

Compounds can be classified as organic or inorganic. Organic compounds always contain carbon.

These compounds can also contain hydrogen, oxygen, nitrogen, and sulfur.

The remaining noncarbon compounds are called inorganic because it contains carbon.

Compounds

Objectives Explain what a chemical bond is Distinguish between covalent, ionic, and

metallic bonds, and give an example or each Describe valence

18-4 Chemical Bonding

The force that binds atoms together is called a chemical bond

Bonding occurs when atoms gain, lose, or share electrons in their outer energy level.

There are three common types of chemical bonds: Covalent Ionic Metallic

Chemical Bonding

Covalent bonds occur when atoms share electrons

Compounds formed by covalent bonds generally melt at low temperatures and do not conduct electricity when in solutions.

Examples include: carbon dioxide, water, ozone, sugar

Covalent

Ionic bonds form when electrons are exchanged between atoms rather than being shared

Compounds formed by ionic bonds generally melt at high temperatures and conduct electricity when in a solution

Ions are atoms that gain or lose electrons; they have different properties than the original atom

Cations, positive ions, form when atoms lose electrons Anions, negative ions, form when atoms gain electrons Examples include sodium chloride, iron oxide.

Ionic Bonds

Metallic bonds result from the attraction between positive ions and surrounding electrons.

Metallic bonds are similar to ionic bonds Examples include copper, gold, silver,

mercury

Metallic Bonds

Each atom has a specific number of electrons that can be given or received to form a bond.

This number of electrons is called the atom’s valence.

Chemical Bonding