CH. 2.1MATTER AND CHANGE

CH. 2.1DESCRIBING 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.

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 → NaClSodium + 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

ElementEx: Sodium Na

CompoundEx: Sodium Chloride

Homogeneous

Mixture:Uniform; also called

a SolutionEx: Salt in Water

Heterogeneous Mixture:

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 chromatographySeparating 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

• 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.