Chapter 15

Classification of Matter

Pure Substances• Materials are made of a pure substance or a

mixture of substances• A pure substance, or substance, is a type of

matter with a fixed composition• A substance can either be an element or a

compound ex. Helium, Water, Salt

Elements• All substances are built from atoms• If all atoms in a substance have the same

identity, the substance is an element• Ex. Copper, gold, silver

All of the elements are found on the Periodic Table

Compounds• Two or more elements can combine to form a

compound• A compound is a substance in which the atoms of

two or more elements are combined in a fixed proportionEx. Table Salt

- Compounds have properties different from the elements that compose them

- Definite Ratio- Can only be decomposed into elements by

chemical rxns. (can’t physically separate them)

Mixtures• A mixture is a material made up of two or more

substances that can be easily separated by physical means• Components retain their own identifying

properties• No definite composition• Can be separated by dissolving, filtering,

evaporating, magnetics, screening, etc.• Mixtures can either be heterogeneous or

homogeneous

Heterogeneous mixtures

• A heterogeneous mixture is a mixture where different materials can be distinguished easily

• Some are easily seen while others are not• Ex. Pizza

Homogeneous Mixtures• A homogeneous mixture contains two or

more gaseous, liquid, or solid substances blended evenly throughout• Components can’t be seen with the naked

eyeEx. Soft Drink in a bottle – contains water, sugar, flavoring, coloring, CO2 gas

Solutions• Solution - A homogeneous mixture in which

the components are close to the size of individual particles of the substance and are too tiny to be seen with a microscope and will never settle to the bottom of a container

• Solutions remain constantly and uniformly mixed

Mixtures can occur between and among all phases of matter• Gas/gas (air)• Gas/liquid (oxygen in water)• Liquid/liquid (alcohol in water)• Liquid/solid – (sugar in water)• Solid/solid – (alloy such as steel)

Ex. The addition of 10-30% chromium creates stainless steel

Physical Properties• A physical property of a substance is any

characteristic of a material that you can observe without changing the identity of the substances that make up the material• Physical properties can be observed directly

of measured with a tool

• Examples of physical properties include boiling point, color, shape, size

Boiling/Freezing/Melting Points

• Boiling/Melting/Freezing points refer not to the phase change itself, but to a measurement: the temperature at which these changes occur

• Physical properties because the composition of a substance doesn’t change during phase change or when one measures temperature to determine these points

Density• Density is the mass of a substance per unit volume• The density of a particular substance (under

constant conditions) is always the same, regardless of sample size

• The composition of a substance doesn’t change when one measures mass and volume to find density -> physical property

Density = mass volume

Solubility• Solubility – the maximum amount of a solute

(substance being dissolved) that can dissolve in a given volume of solvent (the dissolving medium) at a particular temperature and pressure

• The components of solutions do not chemically combine to form a new substance, therefore solutions are composed of two substances which each retain their own properties -> physical property

Viscosity• Viscosity is a measure of a material’s

resistance to flow• High viscosity fluids take longer to pour than

low-viscosity fluidsThe composition of a fluid doesn’t change when it is poured -> physical property

Electrical Conductivity• A solid is either an electrical conductor or

insulator based on its ability to complete an electric circuit

Physical Changes Review

Any observations/measurement made WITHOUT changing the composition of the matter

ColorTextureDensityOdorSolubilityMelting/boiling point (Any Phase Change)

Physical Change• A change in size, shape, state• Identity of the element/compound does not

change• Change in Shape/Size

• Aluminum Foil cut in half• Chewing your food

• Change in State• Rubbing alcohol evaporates in your hand• Juice box freezes in freezer

Signs of a Physical Change

Any phase change

Change in energy of the particles

What you started off with is what you end up with chemically

Chemical Properties• A chemical property is a characteristic of a

substance that indicates whether it can undergo a change that will alter the composition of the substanceA change of one substance to another

• Ex. The capacity to oxidizeThe capacity to corrodeCombustibility

Chemical Changes• Substance(s) present at the beginning of the

reaction are changed into something new.• You BREAK or MAKE bonds!!• The change can’t be undone

Examples• Gasoline is ignited/burns• Car rusts• Milk goes sour• Bread -> toast• Food digesting in your stomach and small

intestine

Signs of Chemical Change

• Bubbles appear• Something is burning• A precipitate forms (solid appears)• Color Change• Temperature changes• Smell

The Capacity to Oxidize• A substance combines with oxygen to form

a new substance with new properties• The new substance formed is a combination

of the atoms of the original substance and oxygen

• Properties of a substance change during the process of oxidation

Combustibility• Combustion is a special type of oxidation• When combustion occurs, a substance

combines with oxygen to form a new substance with new properties in a process that releases heat and light

The Capacity to Corrode

• Corrosion – the process by which metals naturally combine with oxygen, sulfur, or other nonmetals

• When corrosion occurs, the new substance that is formed is a combination of a metal and a nonmetal

• The properties of a substance change during this process

Conservation of Mass• The mass of all substances present before a

chemical change equals the mass of all the substances that remain after the change (this will be more important later)• Ex. A burning log, even though ashes are left

and weigh less, if you could collect all the gases lost during the burning and measure their masses too, mass would be conserved