Module 5
Chemical Properties
5.01 – Electrons and Bonding
• Combined Elements
– Atoms bond with other atoms to become
stable
– Elements combine to form compounds and
molecules
5.01 – Electrons and Bonding
• Remember Periodic
Trends
– Number of valence
electrons increases as
you move left to right
– All elements in the same
column have the same
number of valence
electrons
• Number of valence
electrons determines how
atom will react with other
atoms
5.01 – Electrons and Bonding
• Remember Lewis Structures to represent
valence electrons
5.01 – Electrons and Bonding
• Stability of an Atom
– Depends on how full the outer
energy level is
– Filled energy levels = stable
– Unfilled energy levels =
unstable
• Octet Rule
– 8 is the number toward stability
– Exceptions to the octet rule is
hydrogen and helium
5.02 – Ionic and Covalent Bonds
• Atoms are electrically
neutral
– Why?
• Ions are not electrically
neutral
– Why?
– Can be negative or positive
• Atoms tend to lose or gain
electrons so they end up
with an outermost occupied
shell that is filled to capacity
• The Periodic table can be
used to determine the type
of ion that an atom tends to
form
5.02 – Ionic and Covalent Bonds
Positive Ion
(cation)
Negative Ion
(anion)
5.02 – Ionic and Covalent Bonds
Ionic Bonds Result from an
Transfer of Valence Electrons
• Result of transfer of electrons forms a
positive ion and a negative ion
• Ionic Bond –
• Ionic Compounds –
• Characteristics of Ionic Bonds –
–
–
–
–
5.02 – Ionic and Covalent Bonds
5.02 – Ionic and Covalent Bonds
Ionic Bonds: One big greedy thief dog!
Ionic bonding can be best imagined as one big greedy dog
steeling the other dog's bone. If the bone represents the
electron that is up for grabs, then when the big dog gains
an electron he becomes negatively charged and the little
dog who lost the electron becomes positively
charged. The two ions (that's where the name ionic
comes from) are attracted very strongly to each other as a
result of the opposite charges.
5.02 – Ionic and Covalent Bonds
• Properties of Ionic Compounds
– Solids at room temperature
– High melting and boiling points
– Dissolve in water and separates into ions
– Conducts electricity
5.02 – Ionic and Covalent Bonds
Covalent Bonds Result from a
Sharing of Valence Electrons
•
•
•
•
Covalent bond –
Covalent Compound –
Molecule –
Characteristics of Covalent Bonds –
–
–
–
–
• Can be single, double, or triple
5.02 – Ionic and Covalent Bonds
5.02 – Ionic and Covalent Bonds
5.02 – Ionic and Covalent Bonds
Covalent Bonds: Dogs of equal strength.
Covalent bonds can be thought of as two or more dogs
with equal attraction to the bones. Since the dogs (atoms)
are identical, then the dogs share the pairs of available
bones evenly. Since one dog does not have more of the
bone than the other dog, the charge is evenly distributed
among both dogs. The molecule is not "polar" meaning
one side does not have more charge than the other.
5.02 – Ionic and Covalent Bonds
• Properties of Covalent Compounds
– Exist as solids, liquids, or gases
– Molecules in covalent compounds easy to
separate
– Lower melting and boiling points
– Generally, do not dissolve in water
– Do not conduct electricity
5.03 – Chemical Formulas
• Chemical Formulas
– The symbols of each element in a molecule of the
substance
– A number indicating how many atoms of each
element are in each molecule of the substance
5.03 – Chemical Formulas
• Subscripts
– Small numbers to the right of the symbol
– Subscripts of 1 are not written
5.03 – Chemical Formulas
• Prefixes
– Indicate the number of atoms in a molecule of the
compound (covalently bonded compounds)
Prefix
di–
tri–
tetra–
penta–
hexa–
Meaning
two
three
four
five
six
Example
sulfur dioxide (SO2)
nitrogen trifluoride (NF3)
carbon tetrachloride (CCl4)
phosphorus pentachloride (PCl5)
sulfur hexafluoride (SF6)
5.03 – Chemical Formulas
• Names of some of the elements
in these compounds are slightly
different from their regular
element names.
• For example, the symbol O by
itself represents the element
oxygen, but when oxygen
combines with carbon to form
CO2, its name changes to oxide.
• In a compound made up of two
elements, the name of the first
element stays the same. The
ending of the second element
changes to –ide.
5.03 – Chemical Formulas
• Some of the compounds above
contain parentheses in their chemical
formulas.
• Parentheses are used for grouping.
5.04 – Hydrogen Hydroxide
• Water is all around us.
• Water is necessary for life on Earth. Let’s look
at some of the special properties of water that
all living things rely on every day.
5.04 – Hydrogen Hydroxide
• A water molecule contains covalent bonds
between the two hydrogen atoms and the
oxygen atom.
5.04 – Hydrogen Hydroxide
• The bonds between oxygen
and hydrogen in water are
called polar covalent bonds.
• In a polar covalent bond, the
electrons spend more time
near one of the atoms than the
other.
• Polar covalent bonds most
commonly form between
atoms of elements that are far
apart on the periodic table.
5.04 – Hydrogen Hydroxide
• the water molecule is said
to be a polar molecule.
• Each water molecule acts
like a tiny, electrically
charged particle.
• The positive "side" of the
water molecule can attract
negatively charged
particles. The negative
"side" can attract positively
charged particles.
5.04 – Hydrogen Hydroxide
• A covalent bond in which the
electrons are shared equally
between the atoms is called a
nonpolar covalent bond.
• Nonpolar covalent bonds
typically form between atoms
of the same element.
• It is important to realize that
most bonds are not completely
polar or completely nonpolar.
Some bonds lie somewhere in
between.
5.04 – Hydrogen Hydroxide
• Bonding Between Water Molecules
• In a glass of liquid water, water molecules will line
up like magnets, with each partially negative oxygen
atom on one molecule attracting a partially positive
hydrogen atom on a different water molecule.
• This attraction forms a type of bond between water
molecules called a hydrogen bond.
• Hydrogen bonds form between water molecules.
They are not as strong as the covalent bonds within
a water molecule.
5.04 – Hydrogen Hydroxide
Special Properties of Water
Freezing of Water
• When water molecules
freeze, they actually move
farther apart and arrange
themselves into rigid
structures resembling sixsided figures, or hexagons.
• As a result, frozen water,
or ice, is less dense than
liquid water. That means
ice will float in liquid
water.
5.04 – Hydrogen Hydroxide
• Unique property of water is
important to fish and all
aquatic life.
• Ponds freeze from the top
down. The ice that forms
floats on top of the water acts
as an insulator.
• This allows the organisms in
the water to survive when the
weather is cold.
5.04 – Hydrogen Hydroxide
Water as a Solvent
• the partial positive
charge of the hydrogen
atom and the partial
negative charge of the
oxygen atom
• water can also dissolve
many other solid ionic
compounds. The
partially charged water
molecules pull apart
the ions.
5.04 – Hydrogen Hydroxide
Water’s Surface Tension
• Water molecules at the surface are
attracted to other water molecules
around them too. They are attracted
to the water molecules directly
beneath them and to those on each
side.
• This causes the surface of the water
to behave as if it were tightened into
an elastic film. The film can actually
support small objects. The ability to
support light objects on the water’s
surface is called surface tension.
• Surface tension also causes small
amounts of water to form small
droplets on blades of grass and other
objects. It is surface tension that
allows some insects to walk on the
surface of ponds.
5.04 – Hydrogen Hydroxide
Specific Heat
• Water has a very high specific
heat.
• When heat is applied to water,
much of the heat energy is used
to break the hydrogen bonds.
That leaves less energy available
to heat up the water. As water
cools down, energy is used to
reform the hydrogen bonds
between the water molecules.
Less energy is released as heat,
so the water cools down slowly.
5.05 – Acids & Bases
• an acid is a compound that increases the
concentration of H+ (hydrogen) ions when
dissolved in water.
• A hydrogen atom is a proton and an electron.
When it loses the electron, it is just a proton.
Hydrogen ions are protons, but they do not
remain alone in water — they chemically bond to
water to form H3O+, or hydronium ions
5.05 – Acids & Bases
• some acids do not contain hydrogen
ions. These compounds, called acid
anhydrides, increase the H+
concentration by reacting with
water.
• Examples include CO2, which
creates carbonic acid in water, and
SO3, which creates sulfuric acid in
water.
• By tradition, acids that contain
hydrogen usually have H as the first
element in the chemical formula.
5.05 – Acids & Bases
• Most acids have some common physical and
chemical properties:
– Sour taste
– Corrosive
– Increases the concentration of hydrogen ions
when added to water
– Forms hydrogen gas when it comes in contact with
a metal
– Forms salt and water when added to a base
5.05 – Acids & Bases
• A base is a compound that increases the
concentration of hydroxide ions present in an
acidic solution. (OH−) when dissolved in water.
5.05 – Acids & Bases
• Many bases contain hydroxide
ions. Their chemical names
reflect this. Here are some
examples:
– Bitter taste
– Slippery feeling
– Increases the concentration of
hydroxide ions when added to
water
– Forms salt and water when
added to an acid
5.05 – Acids & Bases
• pH is a measure of the concentration of H+ ions in
a solution of an acid or base.
• The pH scale plots the concentration of solutions
in a range from 0–14.
• Pure water is a neutral substance and has a pH of
7. Substances with pH values below 7 are acids.
• Substances with pH values above 7 are bases.
5.05 – Acids & Bases
• Molarity is one way of measuring
the concentration of a solution.
We use the abbreviation "M" to
record "molarity."
• A solution with a H+
concentration of 1 M (read "one
molar") contains one mole of H+
ions per liter of solution. One
mole of H+ ions is equal to 6.02 ×
1023 H+ ions.
• When working with acids and
bases it is important to know the
pH of the solution.