Microbiology Chapter 2

What is the nucleus of an atom composed of?

Protons and neutrons

What substance makes up most of the mass in living organisms?

Water

Matter

anything that takes up space and has mass

Atom

the smallest chemical unit of matter

Who proposed the model in which electrons orbit a central nucleus?

Niels H. D. Bohr

Electrons

negatively charged subatomic particles circling a nucleus

Nucleus

structure containing neutrons and protons

Neutrons

Uncharged particles

Protons

positively charged particles

Example of Bohr Model

Electron shells on outside with electrons on them, nucleus contains protons & neutrons

Element

composed of a single type of atom

Atomic number

Equal to the number of protons in the nucleus

Atomic Mass (Atomic Weight)

Sum of masses of protons, neutrons, and electrons

True or false: the sum of protons and neutrons estimates the atomic mass of an atom

TRUE → because electrons are so miniscule

Hydrogen

Sym = H

Atomic Number = 1

Atomic Mass = 1

Significance = component of organic molecules & water; H+ released by acids

Boron

Sym = B

Atomic Number = 5

Atomic Mass = 11

Significance = essential for plant growth

Carbon

Sym = C

Atomic Number = 6

Atomic Mass = 12

Significance = backbone of organic molecules

Nitrogen

Sym = N

Atomic Number = 7

Atomic Mass = 14

Significance = component of amino acids, proteins, nucleic acids

Oxygen

Sym = O

Atomic Number = 8

Atomic Mass = 16

Significance = component of organic molecules & water; OH- released by bases; aerobic metabolism

Sodium (Natrium)

Sym = Na

Atomic Number = 11

Atomic Mass = 23

Significance = principal cation outside cells

Magnesium

Sym = Mg

Atomic Number = 12

Atomic Mass = 24

Significance = component of many energy-transferring enzymes

Silicon

Sym = Si

Atomic Number = 14

Atomic Mass = 28

Significance = component of cell wall of diatoms

Phosphorus

Sym = P

Atomic Number = 15

Atomic Mass = 31

Significance = component of nucleic acids & ATP

Sulfur

Sym = S

Atomic Number = 16

Atomic Mass = 32

Significance = component of proteins

Chlorine

Sym = Cl

Atomic Number = 17

Atomic Mass = 35

Significance = principal anion outside cells

Potassium

Sym = K

Atomic Number = 19

Atomic Mass = 39

Significance = principal cation inside cells; nerve impulses

Calcium

Sym = Ca

Atomic Number = 20

Atomic Mass = 40

Significance = intracellular signaling; muscle contraction

Maganese

Sym = Mn

Atomic Number = 25

Atomic Mass = 54

Significance = enzymes; intracellular antioxidant; photosynthesis

Iron

Sym = Fe

Atomic Number = 26

Atomic Mass = 54

Significance = energy transferring proteins; transports O2 in blood

Colbalt

Sym = Co

Atomic Number = 27

Atomic Mass = 59

Significance = Vitamin B12

Copper

Sym = Cu

Atomic Number = 29

Atomic Mass = 64

Significance = enzymes; photosynthesis

Zinc

Sym = Zn

Atomic Number = 30

Atomic Mass = 65

Significance = enzymes

Molybdenum

Sym = Mo

Atomic Number = 42

Atomic Mass = 96

Significance = enzymes

Iodine

Sym = I

Atomic Number = 53

Atomic Mass = 127

Significance = brown & red algae

Isotopes

Atoms of a given element that differ in the number of neutrons in their nuclei

What are the different types of isotopes?

• stable isotopes

• unstable isotopes (ex: carbon-14)

• radioactive isotopes → release energy during radioactive decay

What is the smallest chemical unit of matter?

atom

What atomic particles orbit around the nucleus?

electrons

The number of protons identifies an element. What characteristic tells us how many protons an atom has?

atomic number

Isotopes are forms of atoms that differ from one another by having varying numbers of what particle?

neutrons

What determines an atom’s chemical behavior?

electrons

• because only they interact

What does an electron shell depict?

the PROBABLE locations of electrons at a given time

True or false: electrons occupy electron shells

TRUE

Valence electrons

electrons in the outermost shell that interact with other atoms

What is the max number of electrons for each shell?

First shell = 2 electrons
Second shell = 8 electrons

Third shell = 18 electrons

Which elements only have 1 shell?

Hydrogen & Helium

What has the same number of valence electrons in the outer shell?

Groups (families)

• moving ACROSS the periodic table left to right

Electrons zip around the nucleus at about 5 million miles
per hour. Why don’t they fly off?

Electronegativity. The nucleus is positive and electrons are negative. Opposites attract.

The positively charged particles in the nucleus of an atom are called

Protons

The atomic number of an element is

the number of protons

The atomic mass of an atom is the sum of the masses of the

protons, neutrons, and electrons

The element carbon has 6 protons and 6 neutrons in its nucleus. Which of the following represents the carbon-14 isotope?

6 protons, 8 neutrons

Valence

combining capacity of an atom

General rules of valence

• positive if atom has electrons to give up

• negative if atom has spaces to fill

• stable when outer electron shells contain eight electrons

Chemical bonds

atoms combine by sharing or transferring valence electrons

Molecule

two or more atoms held together by chemical bonds

Compound

a molecule composed of more than one element

An atom with a total of six electrons would have how many electrons in its inner shell?

Two

An atom with a total of six electrons would have how many valence electrons?

four

What do you call a molecule that contains atoms of two or more different elements?

a compound

Covalent bond

sharing of a pair of electrons by two atoms

Electronegativity

attraction of an atom for electrons

• more electronegative = greater pull from nucleus on electrons

• higher electronegativity = right side of periodic table

• lower electronegativity = bottom of periodic table bc distance between nucleus & valence shell is larger

Nonpolar covalent bond

• shared electrons spend equal amounts of time around each nucleus

• atoms with similar electronegativities

• no poles

True or false: carbon atoms form two nonpolar covalent bonds with other atoms

FALSE - they form four

What atoms do organic compounds contain?

carbon and hydrogen

Polar covalent bonds

• unequal sharing of electrons due to significantly different electronegativities

• most important polar covalent bonds involve hydrogen

• allows for hydrogen bonding

True or false: in polar covalent bonds, the more electronegative atom will have a partial negative, whereas the less electronegative atom will have a partial positive.

TRUE

Ionic bonds

• occur when two atoms with vastly different electronegativities come together

• electrons are transferred from one atom to another; NOT shared

What types of charges can atoms have (ionic bonds)?

Cation - positive

Anion - negative

• they attract each other and form ionic bonds

What do ionic bonds typically form?

crystalline ionic compounds - known as salts

How does the salt crystal dissolve?

When water surrounds an ionic bond, the partial charges are attracted to the water so the ions are no longer attracted to each other.

• This forms electrolytes

What is the name for an atom that has a full positive or negative charge?

ion

Ionic bonds involve electrons being donated from one atom to another. How are electrons treated in covalent bonds?

the electrons are shared

Hydrogen Bonds

• electrical attraction between partially charged H+ and full or partial negative charge on same or different molecule

• Can be bound to Fluorine, Oxygen, Nitrogen

• weaker than covalent bonds but essential for life

  • help stabilize 3-D shapes of large molecules (DNA)

Summary of chemical bonds

How do atoms interact with one another to form chemical bonds?

they share or transfer valence electrons

The more electronegative an atom, the greater the pull its nucleus exerts on

electrons

What drives bonding between atoms?

completing electron valence shells

Which type of chemical bond forms between a cation and an anion?

ionic bond

Chlorine and potassium atoms form ionic bonds, carbon
atoms form nonpolar covalent bonds with nitrogen atoms,
and oxygen forms polar covalent bonds with phosphorus.
Explain why these bonds are the types they are

The Cl and K form an ionic bond due to high electronegativity difference, C and N form a covalent bond due to the least electronegativity difference, and O and P form polar covalent due to intermediate electronegativity difference.

True or false: the numbers and types of atoms never change in a chemical reaction.

TRUE → atoms are neither created or destroyed

Biochemistry involves the chemical reactions of

living things

Chemical reactions

the making or breaking of chemical bonds

Reactants

the atoms, ions, or molecules that exist at the beginning of a reaction

Products

the atoms, ions, or molecules left after the reaction is complete

Synthesis Reactions

• involve the formation of larger, more complex molecules

• require energy

Dehydration synthesis

two smaller molecules are joined by a covalent bond and a water molecule is formed

• anabolic / endothermic

Endothermic reaction

reactions that require energy

Anabolism

all synthesis reactions in an organism

Decomposition Reactions

• break bonds within larger molecules to form smaller atoms, ions, and molecules

• water is added

• catabolic / exothermic

Exothermic reaction

reactions that release energy

Hydrolysis

a chemical reaction in which water is used to break down a compound into smaller molecules

Catabolism

all decomposition reactions in an organism

Exchange Reactions

• involve breaking and forming covalent bonds

• have endothermic & exothermic steps

• involve atoms moving from one molecule to another

Metabolism

the sum of all chemical reactions in an organism

Dehydration synthesis is a chemical reaction that joins two molecules through the removal of a hydrogen atom from one and hydroxide from the other, forming a new bond. What molecule is always released during this kind of reaction?

Water

Some chemical reactions require energy in order to occur. What do you call those reactions?

Endothermic

Exchange reactions contain both endothermic and exothermic steps. What other chemical reaction in living things is endothermic?

synthesis reactions

Which equation illustrates a synthesis reaction?

6H2O + 6CO2 → C6H12O6 + 6O2