Concepts of Matter and Energy
Composition of Matter
Molecules and Compounds
Chemical Bonds and Chemical Reactions
- Matter is anything that occupies space and has weight.
- Matter exist in three states: gas, liquid, and solid.
- Energy is the capacity to do work or to put matter into motion.
Energy has kinetic (active) potential (stored) work capacities.
- Types of energy that are important in body functions include,
chemical, electrical, mechanical, and radiant.
- Energy can be converted from one form into another, but some
energy is always unuseable (lost as heat) in such transformations.
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- Elements and atoms
- Each element is a unique substance that can not be decomposed
into simpler substances by ordinary chemical methods. A total of
112 elements exist; they differ from one another in their chemical
and physical properties.
- Four elements (carbon, hydrogen, oxygen, and nitrogen) make
up 96% of living matter. Several other elements are present in small
or trace amounts.
- The building blocks of elements are atoms. Each atom is described
by an atomic symbol consisting of one or two letters.
- Atomic structure
- Atoms are composed of three subatomic particles: protons, electrons,
and neutrons. Because all atoms are electrically neutral, the number
of protons in any atom is equal to its number of electrons.
- The planetary model of the atom portrays all the mass of the
atom (protons and neutrons) concentrated in a minute central nucleus
(Figure 2.1). Electrons
orbit the nucleus along specific orbits. The orbital model also
locates protons and electrons in a central nucleus, but it depicts
electrons as occupying areas of space called orbitals and forming
an electron cloud of negative charge around the nucleus.
- Each atom can be identified by an atomic number, which is equal
to the number of protons contained in the atom's nucleus.
- The atomic mass number is equal to the sum of the protons and
neutrons in the atom's nucleus.
- Isotopes are different atomic forms of the same element; they
differ only in the number of neutrons in the nucleus. Many of the
heavier isotopes are unstable and decompose to a more stable form
by ejecting particles of energy from the nucleus, a phenomenon called
radioactivity. Such radioisotopes are useful in medical diagnosis
and treatment and in biochemical research.
- The atomic weight is approximately equal to the mass number
of the most abundant isotope of any element.
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- A molecule is the smallest unit resulting from the binding of two
or more atoms. If the atoms are different, a molecule of a compound
- Compounds exhibit properties different from those of the atoms
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- Bond formation
- Chemical bonds are energy relationships. Electrons in the outermost
energy level (valence shell) of the reacting atoms are active in
- Atoms with a full valence shell (2 electrons in shell 1, or
8 in the subsequent shells) are chemically inactive. Those with
an incomplete valence shell interact by losing, gaining, or sharing
electrons to achieve stability (that is, to fill the valence shell).
- Ions are formed when valence-shell electrons are completely
transferred from one atom to another. The oppositely charged ions
formed attract each other, forming an ionic bond. Ionic bonds are
common in salts (Figure 2.2).
- Covalent bonds involve the sharing of electron pairs between
atoms (Figure 2.3). If
the electrons are shared equally, the molecule is a nonpolar covalent
molecule. If the electrons are not shared equally, the molecule
is a polar covalent molecule. Polar molecules orient themselves
toward charged particles.
- Hydrogen bonds are fragile bonds that bind together different
parts of the same molecule (intramolecular bonds). They are common
in large, complex organic molecules, such as proteins and nucleic
acids and between water molecules (Figure
- Patterns of chemical reactions
- Chemical reactions involve the formation or breaking of chemical
bonds. They are indicated by the writing of a chemical equation,
which provides information about the atomic composition (formula)
of the reactant(s) and product(s).
- Chemical reactions that result in larger, more complex molecules
are synthesis reactions; they involve bond formation (Figure
- In decomposition reactions, larger molecules are broken down
into simpler molecules or atoms. Bonds are broken (Figure
- Exchange reactions involve both the making and breaking of
bonds. Atoms are replaced by other atoms (Figure
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- Inorganic compounds
- Inorganic compounds making up living matter do not contain
carbon. They include water, salts, acids, and bases.
- Water is the single most abundant compound in the body. It
acts as a universal solvent in which electrolytes (salts, acids,
and bases) ionize and in which chemical reactions occur, and it
is the basis of transport and lubricating fluids. It slowly absorbs
and releases heat, thus helping to maintain homeostatic body temperature,
and it protects certain body structures (e.g., the brain) by forming
a watery cushion. Water is also a reactant in hydrolysis reactions.
- Salts in ionic form are involved in nerve transmission, muscle
contraction, blood clotting, transport of oxygen by hemoglobin,
cell permeability, metabolism, and many other reactions. Additionally,
calcium salts (as bone salts) contribute to bone hardness (Figure
- Acids are proton donors. When dissolved in water, they release
hydrogen ions (H+). Strong acids dissociate completely; weak acids
- Bases are proton acceptors. The most important inorganic bases
are hydroxides (OH-). Bicarbonate ions are important bases in the
body. When bases and acids interact, neutralization occur that is,
a salt and water are formed.
- pH is a measure of the relative concentrations of hydrogen
and hydroxyl ions in various body fluids. Each change of one pH
unit represents a 10-fold change in hydrogen (or hydroxyl) ion concentration.
A pH of 7 is neutral (that is, the concentrations of hydrogen and
hydroxyl ions are equal). A pH below 7 is acidic; a pH above 7 is
alkaline (basic) (Figure 2.9).
- Normal blood pH ranges from 7.35 to 7.45. Slight deviations
outside this range can be fatal.
- Organic compounds
- Organic compounds are the carbon-containing compounds that
living matter comprises. Carbohydrates, lipids, proteins, and nucleic
acids are examples. They all contain carbon, oxygen, and hydrogen.
Proteins and nucleic acids also contain substantial amounts of nitrogen.
- Carbohydrates contain carbon, hydrogen, and oxygen in the general
relationship (CH2O) their building blocks are monosaccharides. Monosaccharides
include glucose, fructose, galactose, deoxyribose, and ribose, disaccharides
include sucrose, maltose, and lactose; and polysaccharides include
starch and glycogen (Figure
2.10). Carbohydrates are ingested as sugars and starches. Carbohydrates,
and in particular glucose, are the major energy source for the formation
- Lipids include the neutral fats or triglycerides (glycerol
plus three fatty acid chains) (Figure
2.11), phospholipids, and steroids (most importantly, cholesterol).
Neutral fats are found primarily in adipose tissue, where they provide
insulation and reserve body fuel. Phospholipids and cholesterol
are found in all cell membranes. Cholesterol also forms the basis
of certain hormones, bile salts, and vitamin D. Like carbohydrates,
the lipids are degraded by hydrolysis and synthesized by dehydration
- Proteins are constructed from building blocks called amino
acids; 20 common types of amino acids are found in the body. Amino
acid sequence determines the proteins constructed (Figure
2.12). Fibrous, or structural, proteins are the basic structural
materials of the body. Globular proteins are functional molecules;
examples of these include enzymes, some hormones, and hemoglobin.
Disruption of the hydrogen bonds of functional proteins leads to
their denaturation and inactivation.
- Enzymes increase the rates of chemical reactions by combining
specifically with the reactants and holding them in the proper position
to interact. They do not become part of the product. Many enzymes
are produced in an inactive form or are inactivated immediately
after use (Figure 2.13).
- Nucleic acids include deoxyribonucleic acid (DNA) and ribonucleic
acid (RNA). The building unit of nucleic acids is the nucleotide;
each nucleotide consists of a nitrogenous base, a sugar (ribose
or deoxy ribose), and a phosphate group. DNA (the "stuff" of the
genes) maintains genetic heritage by replicating itself before cell
division and contains the code-specifying protein structure is a
double-stranded helix (Figure 2.14).
RNA acts in protein synthesis to ensure that instructions of the
DNA are executed and is single-stranded (Figure
- ATP (adenosine triphosphate) is the universal energy compound
used by all cells of the body. When energy is liberated by the oxidation
of glucose, some of that energy is captured in the high-energy phosphate
bonds of ATP molecules and is stored for later use (Figure