Matter & Change

What is Chemistry? The study of the composition, structure & properties of matter & the changes it undergoes

Why Study Chemistry? To explain the natural world To prepare for a career To be an informed citizen

The Scientific Method

Mass vs. Matter Mass: the measure of the amount of matter in something Matter: anything that has mass and takes up space.

Mass vs. Weight 1) Mass is a measurement of the amount of matter something contains, while weight is the measurement of the pull of gravity on an object. 2) Mass is measured by using a balance comparing a known amount of matter to an unknown amount of matter. Weight is measured on a scale. 3) The Mass of an object doesn't change when an object's location changes. Weight, on the otherhand does change with location.

Atom vs. Element Atom: the smallest unit of an element that maintains the properties of that element. Element: pure substance made only of one kind of atom (found on the periodic table) You only need 1 atom to call matter an element

What is a Compound? Compound: is a substance that is made from the atoms of two or more elements that are chemically bonded. Ex: H 2 O, glucose (C 6 H 12 O 6 ), NaCl

Classification of Matter Pure Substances vs. Mixtures All pure substances are either elements or compounds!! ***If you can write the chemical formula for a substance it is a pure substance Ex: H 2 O, Ag (silver), CO 2, Pb (lead)

What is a Mixture? Mixture: made up of two or more kinds of matter that retains its own properties and identity. You cannot write a chemical formula for a mixture Ex. Oil/water, pop, ketchup, air.

Be Careful With Mixtures! You may write the chemical formula for the individual components of a mixture but not the mixture as a whole unit. Example: Air (no chemical formula) – Individual components include: N 2, O 2, CO 2

Two Types of Mixtures Homogeneous: same proportion of components It looks uniform/same throughout Ex. Salt water, milk (not spoiled!) Heterogeneous: does not have the same proportion of components Can see more than one substance Ex. oil and water, granola bars

Properties of all Matter Extensive vs. Intensive Extensive Property: DEPENDS on the amount of matter that is present & will change if amount of matter changes Examples: volume, mass and energy - A pencil is 15 cm in length - The chemical reaction gave off 165 kilojoules of energy

Intensive Property: DOES NOT depend on the amount of matter present and will not change if the amount of matter is changed Examples: Color, Boiling/Freezing/Melting Points, Density, Malleability, Ductility - The color of the clown shoes are red - The density of water is 1 g/cm 3 & its bp is 100°C

Quantitative vs. Qualitative Measurements Quantitative – a description of a relevant characteristic that involves a numerical measurement Ex: The bird has a wingspan of 2 meters Qualitative – a description of a relevant characteristic that does not involve a numerical measurement Ex: The bird has a long wingspan

States of Matter Solid: has definite size and shape. Liquid: definite size, not a definite shape (takes the shape of the container it’s in). Gas: no definite size or shape (fills the container it is in). Plasma: no definite size or shape (very energetic, constant electron movement, looks like runny jello, its gooey). Plasma is very rare.

Liquid Versus Aqueous Liquids are chemicals that are in the pure form. The only pure liquid that we work with in chemistry (unless otherwise noted by the teacher) is water, H 2 O. Aqueous solutions are homogeneous mixtures where water acts as a solvent. Examples include: vinegar (HC 2 H 3 O 2 in H 2 O), salt water (NaCl in H 2 O)

Law of Conservation of Mass Mass is neither created or destroyed in chemical reactions The mass of a system may change state (liquid to gas) but is never lost in ordinary chemical reactions For this law to be tested properly a closed system must be used

Physical Properties Physical Properties: are a characteristic feature of a sample that can be observed or measured without changing the identity of the substance Examples: Melting/freezing/boiling points, conductivity, malleability, density, color, hardness, texture, taste, smell, viscosity

Chemical Properties Chemical Properties: are a characteristic feature that relates to a substance’s ability to undergo changes that transform it into another/different chemical To identify this type of property, a chemical change must be performed Examples: Reactivity, Flammability, new color, new smell

Chemical Change A Chemical Change is a change in which one or more substances are converted into different substances A log burning or iron rusting MAKING COOKIES

Indicators of a Chemical Change Color change Precipitation formed (ppt.): when 2 transparent liquids mix and a solid is formed Gas production (fizzing, bubbling) Odor change Explosion, flame or light production Thermal change when no outside energy is added or subtracted from the system

Physical Change A physical change is a change in the substance that DOES NOT involve a change in the identity of the substance Examples: Cutting Hair or melting snow (all changes of state are physical changes)

Phase changes are considered physical changes. (No new substances are being formed.) Melting = solid to a liquid Freezing = liquid to a solid Boiling = liquid to a gas Condensation = gas to a liquid Evaporation = liquid to a gas Sublimation = solid to a gas Deposition = gas to a solid

Property vs. Change Examples The pencil is 15 cm in length (property) The pencil is cut in half and each piece is now 7.5 cm in length (change) The color of phenolphthalein is clear (property) Phenolphthalein is reactive in basic solutions. (property) The color of phenolphthalein changed from clear to magenta when placed in ammonia (change)