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Chapter 2 Chemistry, Matter, and Life 39
High energy bonds
Phos
Phos
Phos
Ribose
Adenine
Figure 2-28 Components of adenosine triphosphate (ATP). Note
the three phosphate groups with high-energy bonds, ribose (a pentose
sugar), and adenine (a nitrogenous base).
Quick Check
2.20 What is the difference between saturated and
unsaturated fatty acids?
2.21 Analysis of a given nucleic acid reveals cytosine, uracil,
adenine, and guanine. Is this nucleic acid DNA or RNA?
2.22 Analysis of an organic compound shows it contains
only C, H, and a relatively small amount of O. Is this
compound likely a carbohydrate, protein, lipid, or
nucleic acid?
of nutrients releases energy that is used to synthesize ATP. In
this way, the nutrient energy is converted to a form that is
usable by the body through the high-energy bonds of ATP.
CHAPTER SUMMARY
Elements
Define matter, element, and atom.
• Matter is anything that takes up space and has weight.
• An element is the simplest form of matter.
• An atom is the smallest unit of an element.
Use chemical symbols to identify elements.
• Chemical symbols are abbreviations used to identify elements.
Structure of Atoms
Illustrate the structure of an atom with a simple diagram
showing the protons, neutrons, and electrons.
• Protons are positively charged particles in the nucleus of an atom
and have a mass of 1 amu.
• Neutrons, also in the nucleus, have the same mass as protons but
have no charge.
• Electrons are negatively charged particles with negligible mass
that are in constant motion in orbits outside the nucleus.
Distinguish between atomic number and mass number
of an element.
• The atomic number of an element is the number of protons in the
nucleus of an atom.
• The mass number of an element is the number of protons plus the
number of neutrons in the nucleus of an atom
Describe the electron arrangement that makes an atom
most stable.
• The most stable atoms have eight electrons in their highest energy
level or shell.
Isotopes
Distinguish between isotopes and other atoms.
• An atom of a given element that has a different number of
neutrons in the nucleus, and consequently a different atomic
weight, is an isotope.
Describe a radioactive isotope.
• A radioactive isotope has an unstable nucleus that decomposes
and releases energy or atomic particles.
Chemical Bonds
Describe the difference between ionic bonds, covalent
bonds, and hydrogen bonds.
• Chemical bonds are forces that hold together atoms.
• An ion is an atom that has lost or gained one or more electrons;
a positively charged ion is a cation; a negatively charged ion is
an anion.
• Ionic bonds are the attraction forces between cations and anions
to form ionic compounds.
• Covalent bonds result when atoms share electrons; atoms may
share more than one pair of electrons, which results in double or
triple covalent bonds; an unequal sharing of electrons results in
polar covalent bonds.
• Hydrogen bonds are intermolecular bonds, or attractions between
molecules, that are formed by the attraction between the
electropositive hydrogen end of a polar covalent compound and
the negative charges of other molecules or ions.