Ch. 2 BASIC CHEMISTRY -...
Transcript of Ch. 2 BASIC CHEMISTRY -...
Copyright © 2010 Pearson Education, Inc.
Matter and Composition of Matter
• Definition: Anything that has mass and
occupies space
• Matter is made up of elements –An
element cannot be broken down by ordinary
chemical means
• Atoms - are unique building blocks for
each element
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Atomic Structure
• Neutrons
• No charge, In atomic nucleus
• Mass = 1 atomic mass unit (amu)
• Protons
• Positive charge,In atomic nucleus
• Mass = 1 amu
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Atomic Structure
• Electrons
• Negative charge ,orbit nucleus
• Mass = 0 amu
• Equal in number to protons in atom
Copyright © 2010 Pearson Education, Inc. Figure 2.1
Helium atom Helium atom
Nucleus Nucleus
Proton Neutron Electron
cloud
Electron
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Energy
• Definition: Capacity to do work or put matter
into motion
• Types of energy:
• Kinetic: energy associated with motion
• Potential: stored (inactive) energy
• Electrical : results from the movement of
charged particles (Na+, K+)
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Identifying Elements
• Atoms of different elements contain different
numbers of protons
• Compare hydrogen, helium and lithium
Copyright © 2010 Pearson Education, Inc. Figure 2.2
Proton
Neutron
Electron
Helium (He) Lithium (Li)
Hydrogen (H)
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Identifying Elements
• Atomic number =
• Mass number =
• Mass numbers of atoms of an element are not
all identical
• Isotopes = atoms of the same element that
differ in the # of neutrons they contain
Copyright © 2010 Pearson Education, Inc. Figure 2.3
Proton
Neutron
Electron
Deuterium (2H) Tritium (3H) Hydrogen (1H)
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Atoms of Elements can combine Chemically to
form Molecules and Compounds
• Molecule: two or more atoms bonded together
(H2 or C6H12O6)
• Compound:
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Chemical Bonds
• Electrons occupy up to seven electron shells
(energy levels) around nucleus
• Octet rule: Except for the first shell which is
full with two electrons, atoms interact in order
to have eight electrons in their outermost
energy level (valence shell)
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Chemically Inert Elements
• Stable and unreactive
• Outermost energy level fully occupied or
contains eight electrons
Copyright © 2010 Pearson Education, Inc. Figure 2.4a
Helium (He)
Neon (Ne)
2e 2e 8e
(a) Chemically inert elements
Valence shell complete
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Chemically Reactive Elements
• Valence shell not fully occupied by electrons
• Tend to gain, lose, or share electrons (form
bonds) with other atoms to achieve stability
Copyright © 2010 Pearson Education, Inc. Figure 2.4b
2e 4e
2e 8e
1e
(b) Chemically reactive elements
Valence shell incomplete
Hydrogen (H) Carbon ©
1e
Oxygen (O) Sodium (Na)
2e 6e
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Ionic Bonds
• Ions are formed by:
• Anions (– charge) have gained one or more
electrons
• Cations (+ charge) have lost one or more
electrons
• Attraction of opposite charges results in: An
ionic bond
Copyright © 2010 Pearson Education, Inc. Figure 2.5
Sodium atom (Na)
Chlorine atom (Cl)
Sodium ion (Na+) Chloride ion (Cl–)
Sodium chloride (NaCl)
+ –
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Covalent Bonds
• Formed by sharing of two or more valence
shell electrons
• Allows each atom to fill its valence shell at
least part of the time
Copyright © 2010 Pearson Education, Inc. Figure 2.7a
+
Hydrogen
atoms
Carbon
atom
Molecule of
methane gas (CH4)
(a) Formation of four single covalent bonds:
or
Resulting molecules Reacting atoms
Copyright © 2010 Pearson Education, Inc. Figure 2.7b
or
Oxygen
atom
Oxygen
atom
Molecule of
oxygen gas (O2)
(b) Formation of a double covalent bond:
Resulting molecules Reacting atoms
+
Copyright © 2010 Pearson Education, Inc. Figure 2.7c
+ or
Nitrogen
atom
Nitrogen
atom
Molecule of
nitrogen gas (N2)
(c) Formation of a triple covalent bond:.
Resulting molecules Reacting atoms
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Covalent Bonds
• Sharing of electrons may be equal
or unequal
• Equal sharing produces:
Electrically balanced nonpolar
molecules
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Covalent Bonds
• Unequal sharing by atoms with different electron-attracting
abilities produces: polar covalent bonds
• H2O
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Hydrogen Bonds
• Attractive force between electropositive
hydrogen of one molecule and an
electronegative atom of another molecule
• Important in intramolecular bonds, holding a
large molecule in a three-dimensional shape
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(a) The slightly positive ends (+) of the water
molecules become aligned with the slightly
negative ends (–) of other water molecules.
+
–
–
– –
–
+
+
+
+
+
Hydrogen bond
Figure 2.8
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Synthesis Reactions
• A + B AB
• Always involve bond formation
• Anabolic
• Endergonic
Copyright © 2010 Pearson Education, Inc. Figure 2.9a
Example
Amino acids are joined to
Form protein.
(a) Synthesis reactions
Smaller particles are bonded
together to form larger,
molecules.
Amino acid
molecules
Protein
molecule
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Decomposition Reactions
• AB A + B
• Reverse synthesis reactions
• Involve breaking of bonds
• Catabolic
• Exergonic
Copyright © 2010 Pearson Education, Inc. Figure 2.9b
Example
Glycogen is broken down to release
glucose units.
Bonds are broken in larger
molecules, resulting in smaller,
less complex molecules.
(b) Decomposition reactions
Glucose
molecules
Glycogen
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Classes of Compounds
• Inorganic compounds
• Do not contain carbon (ex. Water, salts, and
many acids and bases)
• Organic compounds
• Contain carbon, usually large, covalently
bonded (ex’s. carbohydrates, fats, proteins,
nucleic acids)
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Water
• 60%–80% of the volume of living cells
• Most important inorganic compound in living
organisms because of its properties
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Salts
• Ionic compounds that dissociate into ions in
water
• Ions (electrolytes) conduct electrical currents
in solution
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Acids
• Acids : Proton (H+) donors (release H+ in
solution)
• HCl H+ + Cl–
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Bases
• Bases: Proton acceptors (take up H+ from
solution)
• NaOH Na+ + OH–
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Acid-Base Concentration
• Acid solutions contain higher amounts of H+
• As [H+] increases: acidity increases
• Basic solutions contain higher concentrations
of OH–
• As [H+] decreases (or as [OH–] increases):
alkalinity increases
• pH = measure of the acidity/bascisity of a
solution
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Acid-Base Concentration
• Neutral solutions:
• pH = 7
• Contains equal numbers of H+ and OH–
• Acidic solutions
• [H+], pH
• pH = 0–6.99
• Basic solutions
• [H+], pH
• pH= 7.01–14
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Carbohydrates
• Sugars and starches whose building blocks =
• Three classes
• Monosaccharides -Simple sugars containing
three to seven C atoms (glucose)
• Disaccharides -Double sugars that are too
large to pass through cell membranes
• Polysaccharides - Three/more simple sugars,
e.g., starch and glycogen; not very soluble
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Carbohydrates
• Functions
• Primary role: Major source of cellular fuel
(glucose)
Copyright © 2010 Pearson Education, Inc. Figure 2.15a
Example
Hexose sugars (the hexoses shown
here are isomers)
Example
Pentose sugars
Glucose Fructose Galactose Deoxyribose Ribose
(a) Monosaccharides
Monomers of carbohydrates
Copyright © 2010 Pearson Education, Inc. Figure 2.15b
PLAY Animation: Disaccharides
Example
Sucrose, maltose, and lactose
(these disaccharides are isomers)
Glucose Fructose Glucose Glucose Glucose
Sucrose Maltose Lactose
Galactose
(b) Disaccharides
Consist of two linked monosaccharides
Copyright © 2010 Pearson Education, Inc. Figure 2.15c
PLAY Animation: Polysaccharides
Example
This polysaccharide is a simplified representation of
glycogen, a polysaccharide formed from glucose units.
(c) Polysaccharides
Long branching chains (polymers) of linked monosaccharides
Glycogen
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Lipids
• Insoluble in water
• Main types:
• Triglycerides
• Phospholipids
• Steroids
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Triglycerides
• Defined as:solid fats and liquid oils
• Building blocks = three fatty acids bonded to a
glycerol molecule
• Main functions
• Energy storage
• Insulation
• Protection
Copyright © 2010 Pearson Education, Inc. Figure 2.16a
Glycerol
+
3 fatty acid chains Triglyceride,
or neutral fat
3 water
molecules
(a) Triglyceride formation
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Phospholipids
• Similar to triglycerides:
• Building blocks = Glycerol + two fatty acids
and a phosphorus (P)-containing group
• “Head” and “tail” regions have different
properties
• Important in cell membrane structure
Copyright © 2010 Pearson Education, Inc. Figure 2.16b
Phosphorus-
containing
group (polar
“head”)
Example
Phosphatidylcholine
Glycerol
backbone
2 fatty acid chains
(nonpolar “tail”)
Polar
“head”
Nonpolar
“tail”
(schematic
phospholipid)
(b) “Typical” structure of a phospholipid molecule
Two fatty acid chains and a phosphorus-containing group are
attached to the glycerol backbone.
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Steroids
• Steroids—interlocking four-ring structure
• Examples are cholesterol, vitamin D, steroid
hormones, and bile salts
Copyright © 2010 Pearson Education, Inc. Figure 2.16c
Example
Cholesterol (cholesterol is the
basis for all steroids formed in the body)
(c) Simplified structure of a steroid
Four interlocking hydrocarbon rings form a steroid.
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Proteins
• Building blocks = amino acids
• After amino acids are linked together they often undergo
a natural folding process
• This folding process results in four different levels of
protein structure: primary, secondary, tertiary, quaternary
Copyright © 2010 Pearson Education, Inc. Figure 2.17
(a) Generalized
structure of all
amino acids.
(b) Glycine
is the simplest
amino acid.
(c) Aspartic acid
(an acidic amino acid)
has an acid group
(—COOH) in the
R group.
(d) Lysine
(a basic amino acid)
has an amine group
(–NH2) in the R group.
(e) Cysteine
(a basic amino acid)
has a sulfhydryl (–SH)
group in the R group,
which suggests that
this amino acid is likely
to participate in
intramolecular bonding.
Amine
group
Acid
group
Copyright © 2010 Pearson Education, Inc. Figure 2.19a
(a) Primary structure:
The sequence of amino acids forms the polypeptide chain.
Amino acid Amino acid Amino acid Amino acid Amino acid
PLAY Animation: Primary Structure
Copyright © 2010 Pearson Education, Inc. Figure 2.19b
a-Helix: b-Sheet:
(b) Secondary structure:
The primary chain forms spirals (a-helices) and sheets (b-sheets).
PLAY Animation: Secondary Structure
Copyright © 2010 Pearson Education, Inc. Figure 2.19c
(c) Tertiary structure:
PLAY Animation: Tertiary Structure
Copyright © 2010 Pearson Education, Inc. Figure 2.19d
(d) Quaternary structure:
Two or more polypeptide chains, each with its own tertiary structure,
combine to form a functional protein.
PLAY Animation: Quaternary Structure
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Protein Denaturation
• Shape change and disruption of active sites
due to environmental changes
• A denatured protein is nonfunctional
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Enzymes
• Are proteins
• Biological catalysts
• Increase the speed of a reaction
• Allows for millions of reactions/minute
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Nucleic Acids
• DNA and RNA
• Building blocks = nucleotide, composed of N-
containing base, a pentose sugar, and a
phosphate group
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Deoxyribonucleic Acid (DNA)
• Four Nitrogen containing bases:
• adenine (A), guanine (G), cytosine (C), and
thymine (T)
• Double-stranded, helical
• Replicates before cell division, ensuring
genetic continuity
• Provides instructions for protein synthesis
Copyright © 2010 Pearson Education, Inc. Figure 2.22
Deoxyribose
sugar
Phosphate
Sugar-phosphate
backbone
Adenine nucleotide Hydrogen
bond
Thymine nucleotide
Phosphate Sugar:
Deoxyribose Phosphate Sugar Thymine (T) Base:
Adenine (A)
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
(b)
(a)
(c) Computer-generated image of a DNA molecule
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Ribonucleic Acid (RNA)
• Four bases:
• adenine (A), guanine (G), cytosine (C), and uracil (U)
• Single-stranded
PLAY Animation: DNA and RNA
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Adenosine Triphosphate (ATP)
• Adenine-containing RNA nucleotide with two
additional phosphate groups
Copyright © 2010 Pearson Education, Inc. Figure 2.19
Adenosine triphosphate (ATP)
Adenosine diphosphate (ADP)
Adenosine monophosphate (AMP)
Adenosine
Adenine
Ribose
Phosphate groups
High-energy phosphate
bonds can be hydrolyzed
to release energy.
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Function of ATP
• Phosphorylation:
• The chemical energy contained in the high
energy phosphate bonds can be used to
perform cellular work