Transcript Basic Chemistry Review

Basic Chemistry Review
Matter
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1. Matter refers to anything that takes up space
and has mass
2. All matter (living and nonliving) is composed
of basic elements
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a. Elements cannot be broken down to substances
with different chemical or physical properties
b. There are 92 naturally occurring elements
c. Six elements (C, H, N, O, P, S) make up 98% of
most organisms
Elements Contain Atoms
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1. Chemical and physical properties of atoms depend on the
subatomic particles:
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a. Different atoms contain specific numbers of protons, neutrons, and
electrons
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b. Protons (+ charge) and neutrons (neutral charge) are in nucleus of
atoms; electrons (- charge) move around nucleus
2. Isotopes = atoms with the same number of protons but differ in
number of neutrons; e.g., a carbon atom has six protons but may
have more or less than usual six neutrons
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a. Isotopes used to determine age of fossils and in medical diagnostic
and treatment procedures
Chemical Properties of Atoms
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1. Since protons are positively charged & electrons are
negatively charged they are attracted to each other
2. Arrangement of atom's electrons is determined by
total number of electrons and electron shell they occupy
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a. Energy = capacity to do work
b. Electrons with least amount of potential energy are located in
shell closest to nucleus; electrons having more potential energy
are located in shells farther from nucleus
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c. How atoms react with one another is dependent upon number
of electrons in outer shell
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1) Atoms with filled outer shells do not react with other atoms
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2) In atom with one shell, outer shell is filled when it contains two
electrons
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3) For atoms with more than one shell, the outer shell is stable
when it contains eight electrons
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4) Atoms with unfilled outer shells react with other atoms so each
has stable outer shell
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5) Atoms can give up, accept, or share electrons in order to have a
stable outer shell
Atoms form Molecules and
Compounds
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A. Molecules = two or more atoms of
same or different elements bonded
together (e.g., O2)
B. Compound = molecule of two or more
different elements bonded together (e.g.,
H2O)
Types of Bonds
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1. Covalent bond - involves sharing of electron(s).
Electrons possess energy; bonds that exist between
atoms in molecules contain energy.
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Sharing of a pair of electrons creates a single bond represented
by single dash, e.g. water H2O is made of two single bonds H-OH. Sharing two pairs of electrons is represented by two dashes,
C=C
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Know the number of covalent bonds each of the six most
important elements can form.
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Element# of covalent bonds:Hydrogen-1, Oxygen-2, Nitrogen3, Carbon-4, Phosphorous-5, Sulfur-2
Types of bonds
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2. Ionic bond - electrons are transferred from one
atom to another, e.g. salt NaCl
3. Hydrogen bond - weak attractive force between
slightly positive hydrogen atom of one molecule and
slightly negative atom in another or the same molecule
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a. E.X.: in a water molecule the electrons spend more time
orbiting the oxygen than the hydrogens, therefore the oxygen
becomes slightly negative and the two hydrogens become
slightly positive
b. Such polar molecules attract each other like magnets
Oxidation - reduction:
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1. Oxidation = the loss of electrons (or
loss of hydrogen atoms), a molecule that
loses an electron is oxidized
2. Reduction = the gain of electrons (or
gain of hydrogen atoms), a molecule that
gains an electron is reduced
Water
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A. Life evolved in water
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All living things are 70-90% water
Because water is a polar molecule, water molecules
are hydrogen bonded to each other
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a. hydrophilic molecules - polar molecules attracted to
water molecules
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b. hydrophobic molecules - non-polar molecules repelled
by water
Properties of Water
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1. Water resists temperature changes because hydrogen bonds
between water molecules require a large amount of heat to break
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a. Calorie = amount of heat energy required to raise temperature of
one gram of water 1° C. This is about twice that of other liquids
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b. Water has a high heat of vaporization - takes 540 calories to change
water to a gas
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c. When animals sweat, evaporation of the sweat takes away body
heat, thus cooling the animal
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d. Because water resists temperature changes the earth's surface
temperature is moderate and organisms are protected from rapid
temperature changes, this helps them maintain normal temperatures
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2. Water is universal solvent, facilitates
chemical reactions both outside of and
within living systems
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a. Water is a universal solvent because it
dissolves a great number of solutes
b. Important because living organisms get
and transport most of needed chemicals in
water or water based solutions
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3. Water molecules are cohesive and adhesive
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Cohesion - like molecules cling to each other
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Adhesion - ability to adhere to polar surfaces; water molecules have
positive, negative poles.
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Capillarity - the tendency for a liquid to move upward against pull of
gravity through a narrow space, e.g. water rises up tree from roots to
leaves through small tubes
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1) Adhesion of water to walls of vessels prevents water column from
breaking apart
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2) Cohesion allows evaporation from leaves to pull water column from roots
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4. Frozen water is less dense than liquid water
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a. Below 4° C, hydrogen bonding becomes more rigid
but open, causing expansion
b. Because ice is less dense, it floats; therefore,
bodies of water freeze from the top down
c. This means that ice floats and the bottoms of lakes
and oceans are still available for life and also
insulated during cold weather
Acids and Bases
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1. Water dissociates - has a tendency to spontaneously
break into hydrogen and hydroxide ions:
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2. Acid molecules dissociate in water, releasing
hydrogen ions (H+) ions:
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H20 ---> H+ (hydrogen) + OH- (hydroxide)
Hydrochloric acid (HCl) is a strong acid: HCl ---> H+ + Cl –
3. Bases are molecules that take up hydrogen ions or
release hydroxide ions:
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Sodium hydroxide (NaOH) is a strong base: NaOH ---> Na+ +
OH-
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4. pH scale, which ranges from 0 to 14, is used to indicate the strength of
acids and bases
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a. pH = a measure of hydrogen (H+) ion concentration in a solution
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b. Low pH value indicates a high concentration of H+ ions (acids)
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c. High pH value indicates a low concentration of H+ ions (bases)
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d. pH value of 7 is neutral, i.e. the solution has an equal concentration of H+ and
OH- ions
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e. pH scale is logarithmic, i.e. a ten fold difference for each number
E.X.: pH 4 is 10 times more acidic than 5, and 100 times more acidic than 6
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5. Buffers keep pH steady and within normal
limits in living organisms, e.g. blood pH is 7.4
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a. Buffers stabilize pH of a solution by taking up
excess hydrogen or hydroxide ions
b. Carbonic acid helps keep blood pH within normal
limits
Salts
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Any compound that results from the
chemical interaction of an acid and a base
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Dissociate in solution to become ions
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See common salts on page 47
Solutions
Colloids
Suspensions
Homogeneous
Heterogeneous
Heterogeneous
Particle size: 0.01 - 1 nm; can
be atoms, ions, molecules
Particle size: 1 1000 nm,
dispersed; can be
aggregates or
large molecules
Particle size: over
1000 nm,
suspended; can be
large particles or
aggregates
Do not separate on standing
Do not separate
on standing
Particles settle out
Cannot be separated by
filtration
Cannot be
separated by
filtration
Can be separated by
filtration
Do not scatter light
Scatter light
(Tyndall effect)
May scatter light, but
are not transparent
Organic Substances
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Carbohydrates
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Provide energy that cells require
Contribute to cell structure
Built by simple sugar molecules
(monosaccharides)
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Lipids (Fat, Phospholipids, Steroids)
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Supply energy, build cell parts
Basic building block of fat molecules is
combination of glycerol and fatty acids
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Protein
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Serve as structural materials, energy sources, hormones, cell surface
receptors, and enzymes
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Enzymes speed chemical reactions without being consumed
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Amino acids are building blocks of proteins
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Proteins vary in the number and types of amino acids contained and in their
sequence
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Amino acid chain of protein folds into a complex shape that is maintained by
hydrogen bonds
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Excessive heat, radiation, electricity, altered pH, or chemicals can alter
proteins
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Nucleic Acids
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Nitrogen base, pentose sugar, phosphate)
Genetic material and control cellular activities
Nucleic acid molecules composed of mucleotides:
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Adenine A
Guanine G
Cytosine C
Uracil U
Thymine T
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A & G are purines (large 2 ring bases)
C, U, & T are pyrimidines (small single ring bases)
Important Nucleic Acids
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DNA (deoxyribonucleic acid)
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Double stranded polymer (double helix)-twisted
ladder
Nucleotides building are A, G, C, and T
Pentose sugar is deoxyribose
Stores information that cell parts use to construct
specific protein molecules “Blueprint”
Nucleotides held by hydrogen bonds
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A always bonds to T
G always bonds to C
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RNA (ribonucleic acid)
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Help synthesize protein
Pentose sugar is ribose
Single strands of nucleotides
A, G, C, & U (U replaces T)
 A always bonds to U
 G always bonds to C
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Three types of RNA
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Transfer RNA (tRNA)
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Small & clover leaf shaped
Translate messages from mRNA
Messenger RNA (mRNA)
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Long nucleotides that resemble half-DNA
molecules
Carry messages from DNA for building a
polypeptide (amino acid chain)
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Ribosomal RNA (rRNA)
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Forms ribosomes (site of protein synthesis)
Nucleolar organizer