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.
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)
Element
Ex: Sodium Na
Compound
Ex: Sodium Chloride
Mixture
of Substance:
Variable Composition
Homogeneous
Mixture:
Uniform; also called
a Solution
Ex: 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 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
• 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.