- Pure Substances - Mixtures - Physical and Chemical Changes Chapter 2 – Properties of Matter

Chemistry is the study of matter and its changes…… So, what is matter?

Everything that has mass and volume is called matter.

The atom consists of a central, positively charged core, the nucleus and negatively charged particles called electrons that are found in orbits around the nucleus. Ex: Wood is matter…when wood is burned, it gets charred and turns into Carbon The smallest unit of a chemical element that has the properties of an element

Atoms can join together to make millions of different molecules. A molecule is the smallest unit of a substance that exhibits all of the properties characteristic of a substance. Molecules can be made up of two or more different atoms or two or more of the same atom. Example: Cl 2 is a Molecule of two of the same atoms. NaCl is a combination of two atoms.

Pure means “not mixed with anything else.” A pure substance is any matter that has a fixed composition and definite chemical properties. A mixture is a combination of more than one pure substance. Pure Substances vs. Mixtures

Elements Cannot be broken down into simpler substances by chemical changes Compounds Can be broken down into simpler substances by chemical changes, always in a definite ratio Pure substances: element or compound NaCl (salt) Sulfur Sodium bicarbonate H2OH2O

1. Heterogeneous mixture The substances in this kind of a mixture are not spread out evenly. Example: a bottle of liquid salad dressing. Mixtures are classified by how thoroughly the substances mix Suspension – is a heterogeneous mixture where particles will settle out of the solvent over time. Example: muddy water

2. Homogeneous mixture - the substances are spread evenly throughout, a homogeneous mixture is called a solution. -May or may not scatter light Solution –homogeneous mixture that does not scatter light (it’s clear looking). Example: vinegar (water and acetic acid are mixed evenly throughout), sea water, kool- aid, glass Colloid – homogeneous mixture that scatters light. Example: milk, fog or whipped cream Vinegar Milk

Fresh squeezed orange juice. pure water pure iron pure methane pure octane pure silver pure ammonia pure oxygen, pure sodium chloride (salt) NaCl Our Air: Nitrogen & Oxygen tap water 14 karat gold (gold with nickel or copper added) ammonia solution (ammonia mixed with water) vinegar (acetic acid, water, sometimes trace flavorings) iodized salt (sodium chloride with some sodium iodide added) gasoline (various organic compounds)

Some can be separated easily by physical means: rocks and marbles, iron filings and sulfur (use magnet) Differences in physical properties can be used to separate mixtures. Filtration - separates a solid from the liquid in a heterogeneous mixture (by size) – Figure 14, page 50 Separating Mixtures

Components of dyes such as ink may be separated by paper chromatography. Separation of a Mixture

Distillation: takes advantage of different boiling points. Separation of a Mixture

Chemical Property: The way a substance reacts with others to form new substances with different properties…. Physical Property: A characteristic of a substance that can be observed or measured without changing the composition of the substance.

 Properties used to describe matter can be classified as: 1)Extensive – depends on the amount of matter in the sample -mass, volume, length, shape -Intensive – depends on the type of matter, not the amount present - hardness, density, boiling point, color Describing Matter

-Viscosity -Malleability -Ductility -Electrical Conductivity -Heat Conductivity Ex: Oil or Honey is more viscous than water

The ability of a substance to be shaped by hammering or pressure with out breaking

Ductility - The ability for a substance to be drawn out into a wire or thread. The more ductile, then the thinner and longer the wire. Ex: Gold, Platinum, steel, Copper and Tungsten are all very ductile. Gold Platinum Tungsten

Electrical Conductivity The ability of a substance to conduct (or allow) current to flow through it. Ex: metals and tap water are good conductors of electricity but wood and pure water are not good conductors.

Heat (thermal) Conductivity - How easily heat can travel through a substance Ex: Silver and Copper are excellent thermal conductors but Lead, wood or concrete are not good thermal conductors.

 Physical change will change the visible appearance, without changing the composition of the material.  Chemical change - a change where a new form of matter is formed.  Can the change be reversible, or irreversible?? Reversible = Physical Change Irreversible = Chemical Change

Grinding dirt together and causing it to mix and change color. Change of state is a physical change: such as water changing over to steam (water vapor); Melting Ice Tearing Paper Painting Wood Cutting a wire made of Copper Breaking Glass Salt Dissolving in Water fading of dye on your shirt Digestion of food Cooking Decomposition of old leaves Metal rusting Precipitate being formed Glass being melted to make a vase Healing of a wound wood or match burning & producing ash and carbon gas Photosynthesis