CH. 2.1 MATTER AND CHANGE

CH. 2.1 DESCRIBING MATTER Observation: using your senses to describe. White, waxy substance Inference: making a conclusion made of wax.

DESCRIBING MATTER Qualitative: describing matter using the senses. White, smooth, circular, smells like flowers, warm Quantitative: numerically descriptive 8.5 cm high, weighs 85 grams.

DESCRIBING MATTER Extensive Property: depends on the amount of the sample. (can vary from sample to sample even if same substance) Weight, volume, height, shape Intensive Property: depends on type (composition) of substance. (doesn’t change as long as samples are made of same substance) Color, melting point, reaction with other things

GIVE EXAMPLES OF EXTENSIVE AND INTENSIVE PROPERTIES OF THESE 2 SAMPLES OF SILICON

IDENTIFYING SUBSTANCES Physical Property: quality/condition of substance that can be observed or measured w/o changing substance. Color, weight, size, volume ,

IDENTIFYING SUBSTANCES Physical Change: changing the state but not the composition. Melting, boiling, vaporizing, freezing, crushing, dissolving

IDENTIFYING SUBSTANCES Chemical Property: how a substance react with another substance. Iron reacts with oxygen.

Chemical Change: the reaction that takes place when two substances react (Chemical Reaction). Composition changes. (observe bubbling, color change, precipitate) Iron reacts with oxygen to make rust.

COMMON STATES OF MATTER Solid: definite shape and volume Liquid: indefinite shape, flows, definite volume. Gas (Vapor): indefinite shape and volume, flows.

Mixtures, Elements, Compounds Ch. 2.2-2.4 Mixtures, Elements, Compounds

Symbols Chemists use chemical symbols to represent elements Chemical Symbol: 1st 1-2 letters of the name of the element 1st letter is always Capitalized 2nd letter is always lower case Examples: Co = Cobalt; O = Oxygen; Be = Berylium Exception: Some use the letters from the Latin name Examples: Fe = Iron (Ferrum) K = Potassium (Kalium) Cu = Copper (Cuprium)

Formulas Chemists use chemical formulas to represent compounds Compounds: 2 or more elements Examples: NaCl = Sodium Chloride H2O = Water

Breaking up Compounds can be broken down into simpler substances by chemical means, but elements cannot Chemical changes can be used to break down the substances Heating sugar can be heated until it breaks down into solid carbon and water vapor

Properties Properties of compounds differ greatly from the properties of the individual elements that make them up Solid sodium is extremely reactive Chlorine is a gas Combined they make up sodium chloride, aka table salt

Na + Cl2 → NaCl Sodium + Chlorine → Table salt

H2 + O2 → H2O

Classifying mixtures A mixture is a physical blend of two or more components Based on the distribution of the components, mixtures can be classified as heterogeneous or homogeneous mixtures

Heterogeneous mixture: a mixture in which the composition is not uniform throughout Ex: oil and vinegar, sand in water Homogeneous mixture: a mixture in which the composition is uniform throughout Also known as a solution

Homogeneous mixtures Many solutions are liquid, but can also be gas (air) or solids (stainless steel) The term “phase” can be used to describe any part of a sample with uniform composition and properties Homogeneous mixtures have 1 phase

Heterogeneous V. Homogeneous

Distinguishing Substance and Mixtures Matter Substance: Definite Composition (Homogeneous) Mixture of Substance: Variable Composition Element Ex: Sodium Na Compound Ex: Sodium Chloride Homogeneous Mixture: Uniform; also called a Solution Ex: Salt in Water Heterogeneous Non-uniform; Distinct phases Ex: Milk

Separating mixtures Different physical properties can be used to separate mixtures Different BPs or MPs can be used Filtration: separates a solid from a liquid Coffee filters separate grounds from water Distillation: a liquid is boiled to produce a vapor then condensed into a liquid

Paper chromatography Separating a mixture

Chemical reactions Chemical changes are signs of chemical reactions happening Iron reacting with oxygen to form rust Fe + O2 → Fe2O3 During a chemical reaction, the composition of matter always changes

A substance produced in the reaction is the “product” Fe + O2 → Fe2O3 Reactants Products A substance present at the start of a chemical reaction is called a “reactant” A substance produced in the reaction is the “product” Reactants react to produce products

Recognizing chemical reactions Signs a reaction may have occurred: Production of gas or bubbles Change in color Change in temperature Precipitate forms A solid that forms and settles out of a liquid mixture

Law of Conservation of Mass During any chemical reaction or physical change, the mass of the products is always equal to the mass of the reactants Bottom line: you cannot create or destroy matter. Matter is conserved.