Transcript Chapter 4 - Cloudfront.net

Chapter 4
The Structure of
Matter
4.1
Compounds & Molecules
A compound is different from the
elements it contains.
NaCl, Sodium chloride, is totally
different than the metal, sodium, or
the gas, chlorine.
Chemical bonds distinguish
compounds from mixtures
The forces that hold compounds together
are called chemical bonds.
During a chemical reaction chemical bonds
are broken & atoms are re-arranged to
form a new substance.
A compound has a specific formula
The formula for water is H2O
The formula for table sugar is
C12H22O11.
Compounds are always made of
specific elements in specific numbers.
A molecule of water is always H2O.
[two hydrogen atoms bonded to one
oxygen atom.]
Chemical structure illustrates the
bonding within a compound
The way the atoms are arranged in a
compound determine many of its properties.
[water is polar; oil is non-polar]
Two terms are used to specify the positions
of atoms relative to one another.
– 1. Bond length: the average distance between
the nuclei of the 2 bonded atoms
– 2. Bond angle: the angle formed by two bonds
to the same atom
Models of Compounds
A model helps you to “visualize”
something.
1. Ball & stick model: ball is the atom
& the stick is the bond.
2. Structural formulas: use symbols &
lines to depict the structure.
3. Space filling model: can’t “see” the
bonds. [Fig. 4.4 P.111]
Structure
Different structures give compounds
different properties.
Network structure: SiO2 is an ionic
compound which has a strong, rigid
structure. All the angles are the same
o
(109.5 ).
This is why rocks containing SiO2 are hard
& inflexible. It takes a lot of energy to
break these bonds. (high melting point)
Some network bonds are ionic
Some networks are made of bonded
ions (charged particles). NaCl is
made of a network of tightly packed
positive Na+ and negative Cl- ions.
The result is strong, rigid bonds that
have high melting & boiling points.
Ionic bonds occur between a positive
metal ion & a negative nonmetal ion.
Some compounds are molecules
Molecules are made when nonmetals
combine with nonmetals.
The bonds can be weak or strong.
Molecules of gases have little
attraction to each other, so they
spread out & fill any size container.
Strength of attraction between
molecules
Attraction forces are greatest in solids.
Attraction forces are less in liquids, and
even less in gasses. (see data table 4.2 on p. 113)
The higher melting & boiling points of
water are due to the strong bonds within
the water molecule.
Each water molecule is attracted to the
molecule next to it, due to the polar
nature of the molecule.
Teacher demo p.113
4.2
Ionic & Covalent Bonding
Atoms bond when their valence
electrons interact.
When atoms gain or lose electrons
they form ionic compounds.
When atoms share electrons they
form molecules.
4.2
Ionic & Covalent Bonding
Bonds between atoms act like
flexible springs, because they can
bend & stretch without breaking
Ionic Bonds
Ionic bonds occur between ions of
opposite charge.
Metals lose electrons to become
positive ions, called cations.
Nonmetals gain electrons to become
negative ions, called anions.
Ratio’s
NaCl means 1 atom of Na is bonded
to 1 atom of Cl.
The Na+ is attracted to the Cl- (opposites
attract).
Within a network there are millions
of positive ions being attracted to the
millions of negative ions. NaCl is the
formula unit.
The formula unit varies according to
the compound. Ex.: CaF2
Ionic compounds conduct electricity
when melted
Electric current is the result of
moving charges.
When in solid form, ionic compounds
do not conduct electricity because
the ions are locked in position
(crystal).
However, in liquid form, the ions are
free to move about and they do
conduct electricity
Metallic Bonds
Metals conduct electricity, are
malleable & ductile.
Electrons move freely between metal
atoms. “sea of electrons”
The atoms are packed so closely that
the valence electrons overlap each
other
(sea of electrons). This frees up the
electrons to move from atom to
atom.
Remember, electricity is the result of
moving charges.
Covalent Bonds
Covalent bonds form molecules
(nonmetals bonding to nonmetals)
Covalent compounds can be solid,
liquid or gas.
Most covalent substances have low
melting points.
Covalent bonds do not conduct
electricity.
Covalent bonds share electrons
Electrons are shared so that both
atoms achieve the “magic number”
of chemistry – 8, valence electrons.
If the shared electrons are equally
attracted to each nucleus, they
produce a nonpolar covalent bond.
The sharing is represented by a
single line between the atoms. See p.119
Atoms may share more than 1 pair
of electrons
In a double covalent bond, 2 pairs of
electrons are shared.
In a triple covalent bond, 3 pairs
electrons are shared.
Triple bonds are stronger than
double bonds.
Triple & double bonds are shorter
than single bonds.
Electrons are not always equally
shared
In some instances electrons are
attracted more to one nucleus than
another.
This results in a polar molecule.
Usually electrons are more attracted
to elements on the upper right side
of the Periodic Table.
Water is a good example of a polar
molecule.
Polyatomic ions
Some compounds have both ionic and
covalent bonds; such compounds contain
polyatomic ions.
Polyatomic ions are groups of covalently
bonded atoms that have either lost or gained
electrons.
Polyatomic ions act just like normal ions.
Parentheses are used to denote when more
than one ion is bonded to another.
The corresponding subscript indicates that
everything inside the parentheses is effected
by that subscript.
Naming the polyatomic ions
-ite & -ate are suffixes that indicate the
presence of oxygen.
These endings do NOT tell you how many
oxygen atoms are present.
If there is –ate at the end of the name,
there is 1 more oxygen atom than if there
is an –ite at the end.
The charge is the same for each ion
Some have neither –ite or –ate, these
don’t follow the rules.
4.3
Compound Names & Formulas
Naming ionic compounds – cations &
anions form compounds with strong
bonds.
Both elements’ names are represented in
the name. Ex.: BaF2 is Barium Fluoride.
In many cases, the name of the cation is
simply the name of the element.
When the anion is made of 1 element, the
anion has a name similar to the name of
the element but the ending is different. See
fig. 4.5 on p. 124
Some cation names reflect the
charge
According to what we have learned, FeO
and Fe2O3 should both be called iron
oxide.
Iron (Fe) is a transition metal.
Transition metals can lose 1 or 2 or 3
valence electrons. To distinguish between
the two a Roman numeral is added in
parentheses.
The Roman numeral tells the charge
3+
Iron (III) oxide tells us iron is Fe (a
cation that lost 3 electrons).
Determining the charge of
transition metals
Total charge of every compound must be
zero.
In Fe2O3 there are 3 oxygen atoms.
Oxygen & all elements in column 6 have
oxidation #’s of 23 oxygen atoms times – 2 charge = -6
To total zero for the whole compound, iron
must have a charge of +6.
There are 2 iron atoms, so each must
have a +3 charge
Therefore we are working with iron (III)
Naming Covalent Bonds
With two element covalent bonds,
numerical prefixes tell us the number
of atoms present in the compound.
If there is only 1 atom of the 1st
element listed, there is no prefix. For
2 atoms use the prefix di-, for 3
atoms tri- etc.
The element furthest to the right on
the Periodic Table is named 2nd &
ends in -ide
Naming Covalent Compounds
MonoDiTriTetraPentaHexaHeptaOctaNonaDeca-
One
Two
Three
Four
Five
Six
Seven
Eight
Nine
Ten
Naming Covalent Compounds
BF3
N2O4
Boron trifluoride
Dinitrogen tetroxide
A compound’s simplest formula is
its empirical formula
Empirical formula: the smallest whole
number ratio of the atoms in a compound.
We use the molecular formula to denote
exactly how many atoms are in one
molecule of a compound.
Some compounds have the same empirical
formula, but different molecular formulas.
For example, formaldehyde, CH2O; acetic
acid, C2H4O2; & glucose, C6H12O6 – all have
the empirical formula of CH2O
4.4
Organic & Biochemical Compounds
An organic compound is a covalently
bonded compound made of molecules.
Organic compounds contain carbon &
usually hydrogen.
When a compound has only carbon &
hydrogen it is called a hydrocarbon.
Methane, CH4, has 4 single bonds.
Methane is formed when living matter
decays.
Carbon can also form double bonds when
it shares 2 of its electrons. Triple bonds
are also possible but carbon can never
forms more than 4 bonds.
Alkanes
An alkane is a hydrocarbon that has
only single bonds – like we
mentioned for CH4.
Alkanes can have C-H bonds or C-C
bonds.
Alkanes names end in –ane.
Alkenes
Hydrocarbons that have at least 1
double bond, C=C
Alkenes names end in –ene.
Alcohols
Alcohols are organic compounds that
contain hydrogen, carbon & oxygen.
Alcohols have hydroxyl or –OH
groups
Polymers
A polymer is a large organic molecule made of
many smaller bonds.
Small organic molecules bond to form long
chains called polymers.
Polymers are found in your body, wood, rubber
& plastic.
Rubber, wood, cotton are examples of natural
polymers.
Man-made polymers are usually either plastic
or fibers.
The structure determines its properties, just as
for other compounds.
Polymers are likened to a bowl of spaghetti,
tangled but can slide over one another.
Biochemical Compounds
A biochemical compound is any organic
compound that is important to living
things.
Some examples include carbohydrates for
energy & proteins that form all the organs
in our body.
Carbohydrate: any organic compound that
is made of carbon, hydrogen & oxygen &
that provides nutrients to the cells of
living things.
Proteins
A protein is a biological polymer made of
bonded amino acids.
An amino acid is any of 20 different
naturally occurring organic molecules that
combine to form proteins.
Amino acids (there are 20) are made C, H,
O, & N.
How they combine determines the protein.
Proteins are long chains of amino acids.
DNA is a polymer w/complex
structure
DNA determines entire genetic make
up & is made of C, H, O, N & P.
DNA has the shape of a twisted
ladder known as a double helix.
Every cell in your body has a copy of
your genetic make up.