Bell Work
Ionic and Covalent Compounds
Ions and molecules can combine to form
compounds. Because there are millions
of compounds, scientists organize them
into groups. One way compounds are
grouped is by the kind of chemical bond
they have. A chemical bond is the
combining of atoms to form molecules
or compounds.
• Ionic and Covalent
Compounds
• Bonding can occur between the
valence electrons of different
atoms. The behavior of valence
electrons determines if an ionic
compound or a covalent
compound is formed.
• Ionic Compounds and Their
Properties
• The properties of ionic compounds
are a result of strong attractive
forces called ionic bonds. An ionic
bond is an attraction between
oppositely charged ions. The
compounds that contain ionic
bonds are called ionic compounds.
• Ionic Compounds and Their
Properties
• Ionic compounds can be formed by
the reaction of a metal with a
nonmetal. Metal atoms become
positively charged ions and the
nonmetal atoms become negatively
charged ion when the electron is
transferred. Sodium chloride,
table salt, is an ionic compound.
• Ionic Compounds Properties
• Brittleness - Ionic compounds tend to be
brittle solids at room temperature, so they
usually break apart when hit. High Melting
Points - Strong ionic bonds have high
melting points. This is why most ionic
compounds are solids at room temperature.
Solubility and Electrical Conductivity Many ionic compounds are highly soluble
and dissolve easily in water. The solution
that forms when an ionic compound
dissolves in water can conduct an electric
current because the ions are charged and are
able to move freely past each other.
• Covalent Compounds and Their
Properties
• Most compounds are covalent
compounds. Covalent compounds are
compounds that form when a group of
atoms shares electrons. The group of
atoms that make up a covalent
compound is called a molecule.
• Covalent Compounds Properties
• Low Solubility Most covalent compounds are not
soluble in water. Low Melting Points The forces of
attraction between molecules of covalent compounds
are much weaker than the bonds holding ionic solids
together, so less heat is needed to separate the
molecules of covalent compounds. Low Electrical
Conductivity Although most covalent compounds do
not dissolve in water, some do. Most of the covalent
compounds that dissolve in water form solutions that
have uncharged molecules. Some covalent compounds
do form ions when they dissolve in water. Many acids,
for example, form ions in water and these solutions do
conduct electricity.
• Organic compounds are
covalent compounds
composed of carbonbased molecules. More
than 90% of all
compounds belong to this
group.
• All organic compounds
contain carbon. Each
carbon atom has four
valence electrons so each
carbon atom can make
four bonds with four
other atoms.
• Organic compounds may
also contain hydrogen,
oxygen, sulfur, nitrogen,
and phosphorus.
• Carbon atoms bond
together to form a
structure called a
backbone. It makes the
molecule very strong.
There are three types of
structures for organic
compounds.
• Many organic compounds contain
several kinds of atoms, but some
contain only two. Organic
compounds that contain only
carbon and hydrogen are called
hydrocarbons.
• Organic compounds
made by living things are
called biochemicals.
Biochemicals are divided
into four categories:
carbohydrates, lipids,
proteins, and nucleic
acids.
• Carbohydrates are
biochemicals composed
of one or more simple
sugar molecules bonded
together. Carbohydrates
are used as a source of
energy.
• Lipids are biochemicals
that do not dissolve in
water. Fats, oils, and
waxes are kinds of lipids.
Lipids are also used to
store some vitamins.
• Lipids store excess
energy in the body.
When an organism has
used up most of its
carbohydrates, it can
obtain energy by
breaking down lipids.
• Proteins are biochemicals
composed of “building
blocks” called amino
acids. Amino acids are
small molecules made up
of carbon, hydrogen,
oxygen, and nitrogen
atoms, and sometimes
sulfur atoms.
• Most of the biochemicals
found in living things are
proteins. Proteins
function in the body to
regulate chemical
activities, transport and
store materials, build and
repair body structures,
and regulate processes.
• Nucleic Acids
• The largest molecules made
by living organisms are
nucleic acids. Nucleic acids
are bio-chemicals made up
of nucleotides. Nucleotides
are molecules made of
carbon, hydrogen, oxygen,
nitrogen, and phosphorus
atoms.
• There are only five kinds
of nucleotides, but
nucleic acids may have
millions of nucleotides
bonded together.
• Nucleic acids have
several functions. One
function is to store
genetic information. They
also help build proteins
and other nucleic acids.
• Nucleic acids are
sometimes called the
blueprints of life,
because they contain all
the information needed
for a cell to make all its
proteins.
• DNA and RNA There are two
kinds of nucleic acids: DNA and
RNA.
• DNA (deoxyribonucleic acid) is
the genetic material of the cell.
DNA molecules can store a
huge amount of information -DNA molecules in a single
human cell have a length of
about 2 m.