Chapter 2 Matter and Energy

2.1 Properties of Matter Extensive Properties depend on the amount of matter in a sample: mass, volume Intensive properties depend on the type of matter/substance, not the amount: density, color, hardness, conductivity, reactivity, solubility Identifying properties: Physical: density, color, melting point, boiling point Chemical: reactivity

States of Matter Solid: definite shape and volume, lowest energy, particles are closest together and vibrate Liquid: definite volume, particles slide across each other Gas: takes the shape and volume of their container, highest energy, particles are most spread out. Vapor is the gaseous form of what are normally solids and liquids at room temperature,

Physical Changes Composition of the material does not change, although some of the physical properties may change Changes of state: boiling, freezing, melting, condensing Irreversible changes such as breaking, splitting, grinding, cutting and crushing

2.2 Mixtures A mixture is a physical combination of 2 or more substances. Examples: Heterogeneous: a mixture that is not uniform throughout. Examples: Homogeneous: the composition of materials is uniform throughout. Also called a solution. Examples: Separating mixtures: differences in physical properties enable us to separate mixtures Filtration can be used to separates solid from a liquid in a heterogeneous mixture Distillation is the boiling of a mixture of liquids with different boiling points

2.3 Elements and Compounds A substance that contains 2 or more elements Chemically combined Fixed proportion of elements such as: water always has 2 atoms of hydrogen for every one oxygen Can be broken down into simpler substances by chemical means Examples: Simplest form of matter that has a unique set of properties Cannot be broken down into simpler substances Examples:

Compounds Physical methods that are used to break down mixtures CANNOT be used to separate the substances in a compound. Chemical changes are required to break down a compound into its components such as: heating (not just boiling) and electricity

Pure Substance or Mixture? Substances Composition is fixed Can be separated by physical means Physical combination of 2 or more substances Examples: Composition can vary Cannot be separated physically Element or compound Examples:

The Periodic Table An arrangement of elements into groups based on a set of repeating properties Permits the comparison of properties of one element to another Horizontal rows of the table are called periods and properties vary as you move across a row and and that pattern repeats in the next row. Vertical columns of the table are called groups (or family) and elements in groups have similar chemical and physical properties. Symbols represent elements Chemical Formulas represent compounds

2.4 Chemical Reactions (or chemical changes) A chemical property describes the ability of a substance to undergo a chemical change. While it can help identify a substance, the substance actually undergoes a chemical change and thus becomes a new substance. Reactants are present at the start of a reaction. Products are the substances produced from a reaction. Evidence: transfer of energy (sound, light, heat, electricity) color change, production of gas, formation of a precipitate (a solid that forms and settles out of a liquid mixture)

Conservation of Mass During any chemical reaction, the mass of the products is always equal to the mass of the reactants AKA: The Law of Conservation of Mass states that in any physical or chemical reaction, mass is conserved. Understanding this law and its application is very important to chemistry!!!!!