MicrobiologyB.E Pruitt & Jane J. Stein

AN INTRODUCTIONEIGHTH EDITION

TORTORA • FUNKE • CASE

Chapter 2, part AChemical Principles

Chemistry

• Chemistry is the study of interactions between atoms and molecules.

• The atom is the smallest unit of matter that enters into chemical reactions.

• Atoms interact to form molecules.

Atoms are composed of• Electrons: negatively charged particles, no weight• Protons: positively charged particles, 1 amu• Neutrons: uncharged particles, 1 amu

• Amu = atomic mass unit 6 X 1023 = 1 gram

Atomic weight is the weight of the atom - the sum of it’s parts: protons and neutrons

Atomic number is the number of protons.

The Study of Atoms

• Protons and neutrons are in the nucleus.• Electrons move around the nucleus.

The Study of Atoms

Figure 2.1

• Each chemical element has a different number of protons - it’s atomic number.

• Isotopes of an element are atoms with different numbers of neutrons than typical for that atom. Carbon 14 versus 12. Isotopes of oxygen are:

Chemical Elements

168 O 17

8 O 188 O

Table 2.1

• Electrons are arranged in electron shells corresponding to different energy levels.

Electronic Configurations

Electronic Configurations

Table 2.2.1

Electronic Configurations

Table 2.2.2

• Atoms combine to complete the outermost shell.• The number of electrons in this shell is the valence.

How Atoms Form Molecules: Chemical Bonds

• A compound contains different kinds of atoms.

H2O

• The forces holding atoms in a compound are chemical bonds.

Types of bonds:• Ionic - exchange of electronics making ions• Covalent - shared electrons

• Polar unequal sharing• Hydrogen bonds - between molecules

How Atoms Form Molecules: Chemical Bonds

• The number of protons and electrons is equal in a neutral atom.

• Ions are atoms that have gained or lost electrons and are charged.

How Atoms Form Molecules: Chemical Bonds

Figure 2.2a

• Ionic bonds are attractions between ions of opposite charge. One atom loses electrons and another gains electrons.

Ionic Bonds

Figure 2.2b

• Covalent bonds form when two atoms share one or more pairs of electrons.

Covalent Bonds

Figure 2.3a

• Hydrogen bonds form when a hydrogen atom covalently bonded to an O or N atom in another molecule.

Hydrogen Bonds

Figure 2.4

• The sum of the atomic weights in a molecule is the molecular weight.

• One mole of a substance is its molecular weight in grams.

Molecular Weight and Moles

H2O

2H = 2 1 = 2

O = 16

MW = 18

1 mole weighs 18 g

• Chemical reactions involve the making or breaking of bonds between atoms.

• A change in chemical energy occurs during a chemical reaction.

• Endergonic reactions absorb energy.• Exergonic reactions release energy.

Chemical Reactions

• Occur when atoms, ions, or molecules combine to form new, larger molecules

• Anabolism is the synthesis of molecules in a cell.

Synthesis Reactions

A + B ABAtom, ion,

or molecule A

Atom, ion,

or molecule BNew molecule

AB

• Occur when a molecule is split into smaller molecules, ions, or atoms.

• Catabolism is the decomposition reactions in a cell.

Decomposition Reactions

A + BABAtom, ion,

or molecule A

Atom, ion,

or molecule BNew molecule

AB

Breaksdown into

• Are part synthesis and part decomposition.

Exchange Reactions

NaCl + H2ONaOH + HCl

• Can readily go in either direction.• Each direction may need special conditions.

Reversible Reactions

A + BWater

ABHeat