chapter 2, part a
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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
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