72
UNIT ONE
e. Ions with opposite charges attract and join by ionic
bonds; atoms that share electrons join by covalent
bonds.
f. A structural formula represents the arrangement of
atoms within a molecule.
g. Polar molecules result from an unequal sharing of
electrons.
h. Hydrogen bonds occur between polar molecules.
6. Chemical reactions
a. In a chemical reaction, bonds between atoms, ions,
or molecules break or form.
b. Three types of chemical reactions are synthesis,
in which larger molecules form from smaller
particles; decomposition, in which smaller
particles form from breakdown of larger molecules;
and exchange reactions, in which parts of two
different molecules trade positions.
c. Many reactions are reversible. The direction of a
reaction depends upon the proportion of reactants
and products, the energy available, and the
presence or absence of catalysts.
7. Acids, bases, and salts
a. Compounds that ionize when they dissolve in
water are electrolytes.
b. Electrolytes that release hydrogen ions are acids,
and those that release hydroxide or other ions that
react with hydrogen ions are bases.
c. Acids and bases react to form water and
electrolytes called salts.
8. Acid and base concentrations
a. pH represents the concentration of hydrogen ions
(H
+
) and hydroxide ions (OH
) in a solution.
b. A solution with equal numbers of H
+
and OH
is neutral and has a pH of 7.0; a solution with
more H
+
than OH
is acidic (pH less than 7.0);
a solution with fewer H
+
than OH
is basic (pH
greater than 7.0).
c. A tenfold difference in hydrogen ion concentration
separates each whole number in the pH scale.
d. Buffers are chemicals that resist pH change.
2.3
CHEMICAL CONSTITUENTS OF CELLS
(PAGE 60)
Molecules containing carbon and hydrogen atoms are
organic and are usually nonelectrolytes; other molecules
are inorganic and are usually electrolytes.
1. Inorganic substances
a. Water is the most abundant compound in cells.
Many chemical reactions take place in water. Water
transports chemicals and heat and helps release
excess body heat.
b. Oxygen releases energy needed for metabolic
activities from glucose and other molecules.
c. Carbon dioxide is produced when energy is
released during metabolic processes.
d. Inorganic salts provide ions needed in a variety of
metabolic processes.
e. Electrolytes must be present in certain
concentrations inside and outside of cells.
CHAPTER SUMMARY
2.1
INTRODUCTION (PAGE 51)
Chemistry deals with the composition of substances
and changes in their composition. The human body is
composed of chemicals. Biochemistry is the chemistry of
living organisms.
2.2
STRUCTURE OF MATTER (PAGE 51)
Matter is anything that has weight and takes up space.
1. Elements and atoms
a. Naturally occurring matter on earth is composed of
ninety-two elements.
b. Elements occur most frequently in chemical
combinations called compounds.
c. Elements are composed of atoms.
d. Atoms of different elements vary in size, weight,
and ways of interacting.
2. Atomic structure
a. An atom consists of electrons surrounding a
nucleus, which has protons and neutrons. The
exception is hydrogen, which has only a proton in
its nucleus.
b. Electrons are negatively charged, protons
positively charged, and neutrons uncharged.
c. A complete atom is electrically neutral.
d. The atomic number of an element is equal to
the number of protons in each atom; the atomic
weight is equal to the number of protons plus the
number of neutrons in each atom.
3. Isotopes
a. Isotopes are atoms with the same atomic number
but different atomic weights (due to differing
numbers of neutrons).
b. All the isotopes of an element react chemically in
the same manner.
c. Some isotopes are radioactive and release atomic
radiation.
4. Molecules and compounds
a. Two or more atoms may combine to form a
molecule.
b. A molecular formula represents the numbers and
types of atoms in a molecule.
c. If atoms of the same element combine, they
produce molecules of that element.
d. If atoms of different elements combine, they form
molecules of substances called compounds.
5. Bonding of atoms
a. When atoms combine, they gain, lose, or share
electrons.
b. Electrons occupy space in areas called electron
shells that encircle an atomic nucleus.
c. Atoms with completely F
lled outer shells are
inactive, whereas atoms with incompletely F
lled
outer shells gain, lose, or share electrons and thus
achieve stable structures.
d. Atoms that lose electrons become positively
charged; atoms that gain electrons become
negatively charged.
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