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Chemistry Review
9-16-09
Atoms
 Atoms
are the basic unit of matter. They
are made up of 3 subatomic particles:



Protons
Neutrons
Electrons
 Elements
are pure substances that
consist entirely of one type of atom.


Atomic number- the number of protons
in an atom.
Atomic mass- the number of protons
and neutrons in an atom.

Isotopes- atoms of
the same element
that differ in the
number of neutrons
they contain.
Compounds
 Compounds
are substances formed by
the chemical combination of 2 or more
elements in definite proportions.
Chemical bonds hold the atoms of
a compound together.
 Ionic
bonds- formed when one or more
electrons are transferred from one atom to
another.
 Example: Na + Cl → Na+ + Cl− → NaCl


Cation- atom that loses one or more
electrons.
Anion- atom that gains one or more electrons.

Covalent bonds- forms when electrons are
shared between atoms. The electrons actually
travel in both orbitals.
• Metal – non-metal

Molecules- formed when atoms are joined by
a covalent bond.
Water Molecules

Polarity is present when there is an uneven
distribution of electrons between atoms.
 A water molecule has this distribution because
the Oxygen has a stronger attraction for
electrons than the 2 Hydrogens.
 This uneven distribution causes one end of a
molecule to have a slightly positive charge and
one end to have a slightly negative charge.
 These
slightly opposite charges attract
other water molecules and they are then
joined by a Hydrogen bond.
 Cohesion- an attraction between
molecules of the same substance.

Water is extremely cohesive.
 Adhesion-
an attraction between
molecules of different substances.
 Mixture-
a material composed of two or
more elements or compounds that are
physically mixed together but not
chemically combined.

Example: salt and pepper mixed together.
 Solutions-
mixtures that contain ions
evenly dispersed throughout the solution.


Solute- the substance that is dissolved.
Solvent- the substance in which the solute
dissolves.
 Suspensions-
mixtures of water and a
non-dissolved material.
 Acids
range from 0 to 7 and have a higher
concentration of H+ ions.

Examples:

Bases range from 7
to 14 and have a
higher concentration
of OH- ions.

Examples:
 Pure
water has a pH of 7 and has equal
concentrations of H+ ions and OH- ions. It
is neutral.
 Buffers are weak acids or bases that can
react with strong acids or bases to prevent
sharp, sudden changes in pH.