Transcript General Chemistry, 5th ed. Whitten, Davis & Peck

General Chemistry
Chapter 2 Definitions
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ALLOTROPIC
MODIFICATIONS
(ALLOTROPES)
Different forms of the same element
in the same physical state
ANHYDROUS
Without water
ANION
A negative ion
ATOM
• The smallest particle of an element that
maintains its chemical identity through all
chemical and physical changes.
• Fundamentally consists of: electrons,
protons and neutrons
• Atom contains equal numbers of protons
and electrons
• Atoms are components of molecules
ATOMIC MASS UNIT (AMU)
One twelfth of the mass of an atom of
the carbon-12 isotope; a unit used for
stating atomic and formula weights
ATOMIC NUMBER
• The number of protons in the nucleus of an
atom.
• An atom contains an equal number of
electrons and protons.
ATOMIC WEIGHT
Weighted average of the masses of the
constituent isotopes of an element; the
relative mass of atoms of different
elements.
AVOGADRO’S NUMBER
6.02 x 1023 of the specified items.
CATION
A positive ion.
CHEMICAL FORMULA
Combination of symbols that
indicates the chemical composition of
a substance.
COMPOSITION
STOICHIOMETRY
Describes the quantitative (mass)
relationships among elements in
compounds.
EMPIRICAL FORMULA
The smallest whole-number ratio of
atoms present in a compound;
Also known as the simplest formula
FORMULA
Combination of symbols that
indicates the chemical composition of
a substance
FORMULA UNIT
The smallest repeating unit of a
substance- for non-ionic substances,
the molecule
FORMULA WEIGHT
The mass, in atomic mass units, of
one formula unit of substance.
Numerically equal to the mass, in
grams, of one mole of the substance.
This number is obtained by adding
the atomic weights of the atoms
specified in the formula.
HYDRATE
A crystalline sample that contains
water and another compound in a
fixed mole ratio.
Ex: CuCO4.5H2O
ION
• An atom or group of atoms that carries an
electrical charge.
• A positive ion is a cation; a negative ion is
an anion
• Ions are formed when neutral atoms lose or
gain electrons
IONIC COMPOUND
A compound that is composed of
cations and anions.
EX: NaCl
LAWS OF CONSTANT
COMPOSITION
Different samples of a pure compound
always contain the same elements in the
same proportions by mass; this
corresponds to atoms of these elements
in fixed numerical ratios.
Also known the Law of Definite
Proportions
LAW OF MULTIPLE
PROPORTIONS
When two elements, A and B, form
more than one compound, the ratio of
the masses of element B that combine
with a given mass of element A in
each of the compounds can be
expressed by small whole numbers.
MOLAR MASS
The mass of substance in one mole of
the substance; numerically equal to
the formula weight of the substance
Units= g/mol
MOLE
6.02 x 1023 formula units (or
molecules, for a molecular substance)
of the substance under discussion.
The mass of one mole, in grams, is
numerically equal to the formula
(molecular) weight of the substance.
MOLECULAR FORMULA
A formula that indicates the actual
number of atoms present in a
molecule of a molecular substance.
MOLECULE
• The smallest particle of an element or
compound that can have a stable
independent existence.
• Atoms are components of molecules, and
molecules are the components of many
elements and most compounds
MOLECULAR WEIGHT
The mass, in atomic mass units, of
one molecule of a nonionic
(molecular) substance. Numerically
equal to the mass, in grams, of one
mole of such a substance. This
number is obtained by adding the
atomic weights of the atoms specified
in the formula.
MONATOMIC
Consisting of a single atom. The
noble gases exist as monatomic
molecules. Chlorine gas is not
monatomic Cl2
PERCENT COMPOSITION
The mass percentage of each element
in a compound.
PERCENT PURITY
The percentage of a specified
compound or element in an impure
sample.
POLYATOMIC
Consisting of more than one atom.
Elements such as Cl2, P4 and S8 exist
as polyatomic molecules. Examples
of polyatomic ions are ammonium
ion, NH4+, and sulfate ion, SO4-2
STOICHIOMETRY
Description of the quantitative
relationships among elements in
compounds and among substances as
they undergo chemical changes
STRUCTURAL FORMULA
A representation that shows how
atoms are connected in a compound.
DALTON’S ATOMIC THEORY
1.
2.
3.
4.
5.
An element is composed if extremely small indivisible
particles called atoms.
All atoms of a given element have identical properties,
which differ from those of other elements.
Atoms cannot be created, destroyed, or transformed
into atoms of another element.
Compounds are formed when atoms of different
elements combine with each other in small wholenumber ratios.
The relative numbers and kinds of atoms are constant
in a given compound.
Diatomic Molecules
O2, H2, N2, F2, Cl2, Br2, I2
There are two atoms in each of these molecules.
1 mole =? particles
• 6.02 x 1023 particles
• 1 mol He = 6.02 x 1023 He atoms
• 1 mol H2 = 6.02 x 1023 H2 molecules
– Because this is a diatomic molecule,
1 mol H2 = 2(6.02 x 1023) H2 atoms