theanatomyandphysiologylearningsystem4epdfdr-150930024720-lva1-app6891

Chapter 2 Chemistry, Matter, and Life 25
Table 2-2 Important Ions in the Body
Ion Symbol Importance
Calcium Ca 2+ Component of bones and teeth;
necessary for blood clotting and
muscle contraction
Sodium Na + Principal cation in fluid outside cells;
important in muscle contraction and
nerve impulse conduction
Potassium K + Principal cation in fluid inside cells;
important in muscle contraction and
nerve impulse conduction
Hydrogen H + Important in acid-base balance
Hydroxide OH − Important in acid-base balance
Chloride Cl − Principal anion in fluid outside cells
Bicarbonate HCO − 3
Important in acid-base balance
Ammonium NH + 4
Important in acid-base balance;
removes toxic ammonia from body
Phosphate PO 3− 4
Component of bones, teeth, and highenergy
molecules; important in acidbase
balance
Iron Fe 2+ Important component of hemoglobin
for oxygen transport
charged ions. A negatively charged ion is called an anion
(AN-eye-on). A chlorine atom has 17 protons and 17 electrons
to make it electrically neutral. When it gains or picks up an
electron, it still has 17 positively charged protons but now has
18 negatively charged electrons to make it a negatively charged
chloride ion (Cl − ) (see Figure 2-4).
When an atom such as sodium loses or gives up an electron
to another atom such as chlorine, two charged particles called
ions are formed. One is a positively charged cation; the other
is a negatively charged anion. Because of the opposite charges,
the two ions are attracted to each other. The force of attraction
between two oppositely charged ions is an ionic bond.
Oppositely charged ions that are held together by ionic bonds
are called ionic compounds. Sodium chloride (table salt),
formed from sodium ions and chloride ions, is an example of
an ionic compound.
Covalent Bonds
Covalent (koh-VAY-lent) bonds are formed when two atoms
share a pair of electrons. Two hydrogen atoms, for example,
can share their electrons to form a molecule of hydrogen gas.
Because only one pair of electrons is shared, a single covalent
bond is formed (Figure 2-5). Carbon has four electrons in its
outer shell that it can share with other atoms to form covalent
bonds. If it shares these electrons with four hydrogen atoms,
then four single covalent bonds are formed and a molecule of
methane gas results (Figure 2-6).
1p
Two hydrogen atoms each with one proton in the nucleus
and one electron in the energy shell
1p
1p
A molecule of hydrogen gas, H–H (H 2 )
The two hydrogen atoms share an
electron pair to form a single covalent bond
Figure 2-5 Single covalent bond in hydrogen gas.
1p
11p
12n o
17p
11p
12n o
18n o Sodium ion (Na ) Chloride ion (Cl )
17p
18n o
Sodium atom (Na)
Chlorine atom (Cl)
Sodium chloride
Figure 2-4 Formation of ionic bonds. An electron is transferred from the outer shell of the sodium
atom to the outer shell of the chlorine atom. This transfer results in a positively charged sodium
ion and a negatively charged chloride ion. The opposite charges attract to form the ionic bond
of sodium chloride.