chp 8.1 notes

8.1 Compounds and Chemical Bonds
Compounds: a substance whose
smallest particles include more than
one element chemically bonded
Example: H2O is a compound of
hydrogen and oxygen atoms bonded
Mixture: a substance that includes
more than one type of element
and/or compound NOT bonded
Most matter is in the form of
Our atmosphere is a mixture of
nitrogen and oxygen molecules.
Nitrous Oxide (N2O) is a compound
because oxygen and nitrogen atoms
are bonded together into one
Virtually everything you eat is a
compound: Salt is a compound of
sodium and chlorine: NaCl
Sugar is a compound of carbon,
hydrogen, and oxygen.
Glucose: C6H12O6
Body turns carbohydrates into glucose, the preferred energy sugar of the
body. Stored in muscles and liver until needed.
Fructose: C6H12O6
Found in fruits and sugar cane; body turns excess in to fat
Most matter is in the form of blends
of compounds. All sugars taste
sweet, but fructose tastes much
sweeter than glucose.
There are thousands of different
compounds in a single sample of
animal or vegetable tissue.
p. 159 Molecules and covalent
Chemical bond: a bond formed
between atoms through sharing or
transferring of electrons
Almost all elements form chemical
bonds easily.
Covalent bond: a type of chemical
bond formed by shared electrons
Example: There are two covalent
bonds in a water molecule, between
the oxygen and each of the
hydrogen atoms. Each bond
represents one electron. The
electrons are SHARED not
4 Examples of molecules held
together by covalent bonds:
Double bond:
(2 electrons)
Triple bond:
Ammonia (NH3):
Methane (CH4):
(3 electrons)
Molecule: a group of atoms held
together by covalent bonds in a
specific ratio and shape
P160: Chemical formulas and
Chemical formula: identifies the
number and element of each type of
atom in a compound
For example: Fe2O3 is for a
compound with iron (Fe) and oxygen
(O) in a ratio of 2 iron atoms for
every 3 oxygen atoms.
H2O: The subscript 2 indicates that
there are 2 hydrogen atoms in the
molecule. No subscript means there
is one molecule.
The formula also tells you that water
always contains twice as many
hydrogen atoms as oxygen atoms.
The shape of a molecule is also
important to its function and
properties, so they are represented
by structural diagrams which show
the shape and arrangement.
Of course, real molecules are threedimensional, not flat as shown in the
structural diagram. Methane is
really a 4-sided pyramid called a
P161 Structure and Function
Properties come from the molecule:
properties of a compound depend
MUCH more on the exact
composition and shape than on the
elements of which it is made.
Aspirin (acetylsalicylic acid) is made
from carbon, hydrogen, and oxygen
(H8C9O4) which reduces pain and
fever in humans.
By themselves, H, C, and O do NOT
reduce pain and fever. Polyethylene
plastic wrap and formaldehyde (a
toxic preservative) are also made
from carbon, oxygen, and hydrogen.
If the ratio of elements change, the
resulting molecule would NOT be
Aspirin (C9H8O4)
Acetyl Benzoyl Peroxide (C9H8O4)
Benzodioxole-5 carboxylic acid
methyl ester (C9H8O4)
P162 Ionic Compounds
Ion: an atom that has an electric
charge different from zero. Ions are
created when atoms gain or lose
Ionic Bond: a bond that transfers an
electron from one atom to another
resulting in attraction between
oppositely charged ions.
Not all compounds are made of
molecules. Sodium Chloride (NaCl)
is a compound of Na and Cl in a ratio
of one sodium per chlorine atom. In
Sodium Chloride, the electron is
transferred from the sodium atom
to the chlorine atom. When atoms
gain or lose an electron, they
become ions. An ion is a charged
atom. By losing an electron, sodium
becomes a sodium ion with a charge
of +1. Chlorine gains an electron,
and becomes a chloride ion with a
charge of -1 (when chlorine
becomes an ion, the name changes
to chloride)
Ionic bond: Sodium and chlorine
form an ionic bond because the
positive sodium ion is attracted to
the negative chloride ion. Ionic
bonds are bonds in which electrons
are transferred from one atom to
Ionic compounds do NOT form
The atoms bond through attraction
between positive and negative
Ionic compounds also have ratios of
elements – like one sodium per
chloride ion in sodium chloride.
Sodium involves the transfer of ONE
electron; however, ionic compounds
may also be formed by transferring
two or more electrons.
Example: magnesium chloride
(MgCl2). The magnesium gives up
two electrons to become a
magnesium ion with a charge of +2.
(Mg²+). Each chlorine atom gains
one electron to become a chloride
ion with a charge of -1 (Cl-). The ion
charge is written as a superscript.
P163 Why Chemical Bonds form
Atoms form bonds to reach a lower
energy state.
Energy is released when chemical
bonds form because chemically
bonded atoms have less total energy
than free atoms.
All elements except noble gases
form chemical bonds. However,
some elements are more reactive
than others. “Reactive” means an
element readily forms chemical
bonds with other elements.
Example: Sodium is a highly reactive
metal. Chlorine is a highly reactive
gas. If pure sodium and pure
chlorine are placed together, a
violent explosion occurs as the
sodium and chlorine combine and
form ionic bonds. The explosion is
the energy given off by the
formation of the chemical bonds.
Grease fire in kitchen:
The closer an element is to a noble
gas, the more reactive it is. The
alkali metals are very reactive
because they are just one electron
away from the noble gases. The
halogens are also very reactive
because they are also one element
away from the noble gases. The
beryllium group and the oxygen
group are less reactive because each
element in these groups is two
electrons away from a noble gas.