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Matter, and more!
MatterAnything that has MASS and takes up SPACE
How is Matter classified?
1) Pure Substances
2) Mixtures
1) Pure SubstancesComposition remains the same, does
not depend on a sample = Fixed composition
Homogenous—same throughout.
Example: Compound (NaCl) or Element (Fe)
2) Mixtures 2+ substances combined together
Substances do not change their properties or name.
Able to be separated, not chemically combined.
Possess a combination of properties based on the substances present.
Types of Mixtures1) Homogenous
Uniform compositionAlso known as “true solutions”Ex. Salt-water
2) HeterogeneousNo uniform compositionCan easily see the different components
of the mixtureEx. Italian dressing
Mixture Types---More Detail
True SolutionWhat we normally think of as a “solution”HomogenousSolute/solvent completely dissolved
How are mixtures separated?Thin-Layer Chromatography
Filtration
Centrifuge
Identify whether a substance is pure/mixture and
homogenous/heterogeneous. 1) Salad
2) Kool-Aid
3) Vegetable soup
4) Ca
5) Water
Properties of Matter1) Chemical
Ability to go through changes resulting in a different substance
The substance is no longer the same, different identity
Evidence of chemical reaction: color change, precipitate forms, gas formation, and/or temperature change
Ex. Burning
2) Physical Observed or measured property Substance identity is not changed Ex. melting point, boiling point, density
Classify each change as either chemical or physical.
1)Gasoline in your engine burns as you start the car.
2)Distilled water
3)Rust on a nail
4)Glow sticks
5)Medicine crushed into a powder
The Atom
How far back does the “atom” go?
Democritus400 B.C.Called the basic unit of
matter an atom or “atomos”
Law of Conservation of Mass/Matter
Matter cannot be created or destroyed
Total mass is constant in chemical reactions.
Originated with Antoine Lavoister (1700s) Quantitative mass data of
reactants and products in mercury oxide decomposition.
Law of Definite Proportions
Proposed by Joseph Proust (late 1700s)Decompositions and research with copper
carbonate
Compound composition and properties are fixedAll compound samples have the same
compositionSame % of elements in the compoundEx. H2O
TerminologyElement– basic unit of a substance, contain only
ONE type of atom, represented by symbol.
Example: Ag, only contains Ag atoms.
Atom—smallest particle of an element that still contains element properties.Example: One atom of Au, cannot have a smaller
particle of gold and still be gold.
Compound vs. MoleculeCompounds:
more than one elementelements combined in definite proportions
Molecule:Smallest unit of a compound that still retains the
properties of the compound.
Dalton Atomic Theory1800s
Atoms make up elements.
Atoms form compounds as a whole and cannot be divided. Compounds formed from atoms joining in FIXED proportions
Dalton Atomic Theory (cont.)
All matter made of atoms
Atoms of an element have the same size, mass, etc.
Different atoms have various sizes, mass, etc.
Atoms cannot be divided, destroyed, or created.
Atoms rearrange in chemical reactions.
John Thomson1897
Cathode-Ray experiments.
Discovered the electron particle and its possible charge.
Stated electrons have a negative charge
Determined ratio between mass and charge of an electron
Early Models of the AtomThompson
Must be a balance between negative and positive charges
“Raisin-Pudding” model
Uniform distribution of positive chargePositive cloud with stationary electrons
Early Models of the AtomRutherford
How are electrons distributed in an atom?
Discovered alpha particles as 42He
Experiments with Au, Ag, and Pt foils bombarded with alpha particles
Early Models of the Atom Rutherford
Mostly empty space
Small, positive nucleus
Contained protons
Negative electrons scattered around the outside
Atomic StructureNucleus
ProtonsNeutrons
Electrons
Atomic StructureElectrons
Tiny, very light particles
Have a negative electrical charge (-)
Move around the outside of the nucleus
Atomic StructureProtons
Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom
Atomic StructureNeutrons
Large and heavy like protons
Neutrons have no electrical charge
Located in the nucleus of the atom
Describing AtomsAtomic Number (Z) =
number of protonsIn a neutral atom, the # of
protons = the # of electrons
Mass Number (A)= the number of protons + the number of neutrons
IsotopesThe number of protons for a given atom never
changes.
The number of neutrons can change.
Two atoms with different numbers of neutrons are called isotopes have the same atomic #have different atomic Mass #’sBehave the same chemically
Isotopes
Atomic MassWeighted average of element’s natural isotopes
Some isotopes are more abundant than others….
SO atomic mass leans towards more abundant mass
How do we calculate atomic mass?
1) Masses of Isotopes
2) Fraction of the abundance of each isotope usually a percentage
Average atomic mass = mass contributed by all isotopes Fraction of abundance (isotope mass) = mass from a
particular isotope
Example 1:
Neon has 3 natural isotopes. Ne-20 (90.51%, 19.99244 u)Ne-21 (0.27%, 20.99395 u) Ne-22 (9.22%, 21.99138 u)
What is the weighted average atomic mass for Ne?
Example 2: Two natural copper isotopes are Cu-63 (62.9298 u) and Cu-65 (64.9278 u)
If copper’s atomic mass is given as 63.546 u, what are the percent abundances of these isotopes? Which isotope is the most abundant?
Homework
pp. 66-67 #7, 31-33, 37, 39-42
Finish “Atomic Theory I” worksheet