Combinations of Atoms
Chapter 8.2
Compounds
1.Compounds
a.Elements are rarely found pure in the
earth, they are generally found as
compounds.
b.A compound is a substance that results
when the atoms of two or more elements
are chemically combined.
Compounds
i.The result is a new substance with
properties different from those of
elements that compose it.
ii.Example: Water is a compound
formed from the atoms of hydrogen
and oxygen.
Compounds
a.A molecule is the smallest complete
unit of a compound. Water is formed
from two hydrogen molecules and
one oxygen molecule. H-O-H
b.Diatomic molecules are molecules
that exist naturally as two atoms.
Compounds
i. Hydrogen atoms always exist
naturally as a diatomic
molecule.
ii. The oxygen atoms you breath
are O2 atoms.
Energy Levels
1.Energy Levels
a.Energy levels are the arrangement of
electrons within the electron cloud of an
atom; they are also the specific energies
an atom can have.
i. Atoms have a specific number of energy
levels to contain the amount of electrons they
have.
Energy Levels
a.The electrons in an atom travel
on the energy levels in a set of
“paths” called orbitals.
i.An orbital is the region of space in
the energy level where an electron
is likely to be found.
Energy Levels
The following table describes the energy
levels, orbitals, and # of electrons.
Energy Level
Operation
Orbital
Operation
# of Electrons
1
X Self
1
X2
2
2
X Self
4
X2
8
3
X Self
9
X2
18
4
X Self
16
X2
32
Energy Levels
a.When electrons are in their highest
energy levels the atom is said to be in
an excited state.
b.When electrons are in their lowest
energy levels the atom is said to be in
a ground state.
Energy Levels
a.Atoms with filled energy levels are stable
and do not react. This group of elements
is the “Noble Gases”.
i. Elements that are near the edges of the
period table are the most reactive, because
they are closest to having a complete set of
electrons.
ii.Elements nearest the bottom are also more
reactive because they have more energy
levels.
Chemical Bonds
1.Chemical Bonds
a.A chemical bond is produced by the
interaction of valence electrons (electrons
in the outermost energy) and is the force
that holds atoms together.
b.Atoms can form chemical bonds by either
sharing electrons or transferring
electrons from one atom to another.
Ionic Bonds
a.An ionic bond is a bond formed through
the transfer of electrons from one atom to
another.
i. When an ionic bond is formed, both atoms
become either positively or negatively
charged and are called ions.
ii.An ion is an atom or group of atoms that
carry a charge.
Ionic Bonds
i.When an atom gives away electrons the
atom becomes positively charged and is
called a cation.
ii.When an atom gains electrons the
atom becomes negatively charged and
is called an anion.
Covalent Bonds
1.Covalent Bonds
a.A covalent bond is a bond between atoms
that share electrons.
b.When electrons are shared in a diatomic
molecule the nuclei of each atom pull on
the electrons with the same force and
create a neutral molecule.
Covalent Bonds
a.When electrons are shared in a molecule
of different elements the electrons are
shared unequally.
i. For example, in a water molecule the two
oxygen molecules pull on the electrons
greater than the one hydrogen molecule
which gives the molecule a slightly positive
charge at its hydrogen end and a slightly
negative charge at its oxygen end.
Chemical Formulas
1.Chemical Formulas
a.A chemical formula is symbols indicating the
elements a compound contains and the relative
number of each element.
i. In a compound the number of elements in the same
compounds are always found in the same
proportion.
ii.For example, the chemical formula for water is H2O,
which represents two hydrogen atoms and one
oxygen atom for every H2O molecule.
Mixtures
1.Mixtures
a.A mixture is material that contains
two or more substances that are not
chemically combined.
i.The substances in a mixture keep their
individual properties, and can be
separated by a physical means.
Solutions
a.A solution is a mixture in which one
substance is uniformly dispersed in
another substance.
i. An example of a solution is Kool-Aide. The
sugar is completely dissolved in the water.
ii.Not all solutions are liquids. Gases and solids
can also form solutions.
iii.An alloy is a solution of two or more metals,
such as brass (Cu & Zn) and bronze (Cu &
Sn).