17.1 Notes Composition of Matter

Composition of Matter Pure Substances Substances cannot be broken down into simpler components and still maintain their original properties. Elements – all the atoms in the substance are the same (90 – natural, over 20 synthetic) Compounds – are substances in which the atoms of two or more elements are combined in fixed proportions. (Example : Water)

Composition of Matter continued Mixtures Mixtures are materials that are made up of two or more substances that can be easily separated by physical means. Heterogeneous mixture – different materials can be easily distinguished. (Ex. Granite, Concrete) Homogeneous mixture – two or more gaseous, liquid or solid substances blended evenly throughout. (Ex. Soft drinks, Vinegar)

Composition of Matter Continued Colloids – type of mixture that never settles. (Ex. Paint, fog, smoke) Tyndall effect – scattering of light by colloidal particles. (Ex. Light beam through a solution) Suspension – heterogeneous mixture containing a liquid in which visible particles settle. (Ex. Pond water)

17.2 Properties of Matter Physical Properties - A physical property is any characteristic of a material that you can observe or attempt to observe without changing the identity of the substance. (Ex. Color, shape, size, melting/boiling point, texture, hardness)

Properties of Matter continued… Physical Change A physical change is a change in size, shape or state of matter. These changes accompany energy changes but the identity does not change. (Ex. Cutting paper, tearing paper, coloring water) Distillation – process for separating substances in a mixture by evaporating a liquid and re-condensing its vapor.

Properties of Matter continued… Chemical Properties and Changes A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change. (Ex. Flammability, ability to rust or tarnish, etc.) - A chemical change is the changing of one substance into another substance. (Ex. Burning wood, rust, acid on paper, baking a cake)

Other Important Information Detecting a chemical change You can use smell to detect a chemical change, such as smelling rotten eggs or a dead animal. You can also see a rapid release of energy in some chemical changes.

Weathering Weathering - Weathering can be a physical change if the water that gets into rocks expands causing the rocks to break. Weathering can be a chemical change if water is involved in the breakdown of limestone into soluble compounds.

Law of Conservation of Mass - The law of conservation of mass states that the mass before a chemical change equals the mass of all the substances that remain after the change.