bond together they form a diatonic molecule.When two atoms of different chemi-
cal elements bond, they form a chemical compound.
Atoms are held together because there is an electrostatic attractive force
between the two atoms. Energy is required for the chemical reaction to bond
atoms. This energy becomes potential chemical energy that is stored in a mole-
cule or chemical compound.
For example, combining two atoms of hydrogen forms a hydrogen molecule,
H 2 (Fig. 2-3). Combing a hydrogen molecule consisting of two atoms with one
oxygen atom forms the compound we know as water, H 2 O (Fig. 2-4).
Bonds are formed in two ways:- Gain or lose an electron from the valence shell; called an ionic attraction.
- Share one or more electrons in the valence shell; called a covalent bond.
In reality, atoms bond together using a range of ionic and covalence bonds.
There are four kinds of chemical bonds: - Ionic bond.Transfer electrons from one atom to another atom. An atom
becomes unbalanced when it gains or loses an electron. An atom that gains
an electron becomes negatively charged. An atom that loses an electron
(^30) CHAPTER 2 Chemical Elements of Microorganisms
Fig. 2-4. Water is a compound consisting of two hydrogen atoms and one oxygen atom.
H
O H
O
H
H
- H
H
Fig. 2-3. Hydrogen becomes chemically stable by sharing a valence
electron with another hydrogen atom.