Page 3 - Herlihy: The Human Body in Health and Illness, 3rd Edition

b. Other characteristics of atoms
i. Atomic number: the number of protons in the
nucleus
ii. Atomic weight: the sum of the protons and neutrons
in the nucleus

iii.Isotopes
a. An atom that has the same atomic number but a
different atomic weight (due to different numbers
of neutrons)
b. Unstable isotopes. Give off subatomic particles as
they decay (trying to become stable)
Clinical Correlates Use of I 131 diagnostically and
therapeutically in thyroid disease… radiation
hazards
iv. Electron shells
a. The inner shell holds two electrons
b. Second and third shells hold eight electrons
c. The outer shell (third), if incomplete can receive
or donate electrons ( 2 -8-8)

B. Chemical Bonds (Figure 2-3)
1. Ionic bonds: achieved by the transfer of electrons
between atoms

2. Covalent bonds
a. Formed through the sharing of electrons
b. Excellent example is water, the covalent bonding
between the hydrogen and oxygen W A T E R ( H2O)