Properties of Matter Chapter 2

2-1: Classifying Matter

Pure Substances Pure substance – matter that always has exactly the same composition Table salt and table sugar are two examples of pure substances. Substances can be classified into two categories—elements and compounds.

Elements Element – a substance that cannot be broken down into simpler substances An element has a fixed composition because it contains only one type of atom Examples: The elements oxygen and nitrogen are the main gases in the air you breathe.

Elements Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized. C represents carbon. Al represents aluminum. Au represents gold.

Compounds Compound – a substance that is made from two or more simpler substances and can be broken down into those simpler substances Ex. – Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.

Mixtures Heterogeneous mixture – the parts of the mixture are noticeably different from one another The sand is a heterogeneous mixture of different kinds of grains.

Mixtures Homogeneous mixture – the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.

Solutions Solution – The mixture that forms when substances dissolve and form a homogeneous mixture

2-2: General Properties of Matter

Matter – anything that has mass and volume Properties – characteristics of matter Ex. – Color, odor, shape, texture, and hardness

Mass – The amount of matter in an object The mass of an object does not change unless some matter is either added to or removed from an object

Weight – response of mass to the pull of gravity Gravity – force of attraction between all objects in the universe

Volume – the amount of space an object takes up Measured in liters (L), milliliters (mL), and cubic centimeters (cm3) 1 L = 1000 mL or 1000 cm3 ______ mL = 3.5 L 3500 mL = 3.5 L

Densities of Some Common Substances Density – the mass per unit volume of an object Densities of Some Common Substances Substances Density (g/cm3) Air 0.0013 Gasoline 0.7 Wood (oak) 0.85 Water (ice) 0.92 Water (liquid) 1.0 Aluminum 2.7 Steel 7.8 Silver 10.5 Lead 11.3 Mercury 13.5 Gold 19.3

2-3: Phases of Matter

Phase – state in which matter can exist: solid, liquid, gas or plasma

Sodium Chloride (Table Salt) Solid – matter with a definite shape and a definite volume Crystal – solid in which the particles are arranged in a regular, repeating pattern Quartz Sodium Chloride (Table Salt)

Amorphous solid – solid that loses its shape under certain conditions Sealing Wax

Liquid – matter with no definite shape but with a definite volume Viscosity – the resistance of a liquid to flow Honey has a higher viscosity than water

Gas – matter with no definite shape or volume Plasma – high-energy phase of matter Plasma is one of the most common phases of matter in the universe

2-4: Phase Changes

Solid-Liquid Phase Changes Melting – the change of a solid to a liquid Melting point – the temperature at which a solid changes to a liquid

Solid-Liquid Phase Changes Freezing – the change of a liquid to a solid Freezing point – the temperature at which a liquid changes to a solid The freezing point of a substance is equal to its melting point

Liquid-Gas Phase Changes Vaporization – the change of a substance from a liquid to a gas Evaporation – vaporization at the surface of a liquid

Liquid-Gas Phase Changes Boiling – the process in which particles inside a liquid as well as those on the surface change to a gas

Liquid-Gas Phase Changes Boiling point – temperature at which a substance changes from the liquid phase to the gas phase Boiling point of water – 100 degrees Celsius Boling point of a diamond – 4200 degrees Celsius

Liquid-Gas Phase Changes At high altitudes, air pressure is lower, so the boiling point is reduced. Water will boil at a temperature lower than 100 degrees Celsius at high altitudes

Liquid-Gas Phase Changes Condensation – the change of a gas to a liquid Water vapor in the surrounding air loses heat energy when it comes in contact with the cold glass Water vapor condenses and becomes liquid

Solid-Gas Phase Changes Sublimation – the surface particles of a solid escape directly into the gas phase Ex. – snow turns to water vapor Ex. – dry ice

Heat, Temperature, and Phase Changes Heat is energy that causes the particles of matter to move faster and farther apart. As the particles move faster, they leave one phase and pass into another.

2-5: Chemical Changes

Observing Chemical Properties Chemical property – any ability to produce a change in the composition of matter

Observing Chemical Properties Two chemical properties: Flammability – a material’s ability to burn in the presence of oxygen Reactivity – The property that describes how readily a substance combines chemically with other substances Iron + Oxygen = Rust

Chemical Changes Chemical changes – the changes that substances undergo when they change into new and different substances

Chemical Changes A change in color is a clue that a chemical change has produced at least one new substance (most of the time) As a match burns, it shrivels up and turns black.

Physical Property Physical property can be observed with senses and can be determined without destroying matter

Physical Changes Physical change – a change in size, shape, or state of a substance but no new substance is formed