Transcript Chapter 2

Chapter 2
Introductory Chemistry
Copyright 2010, John Wiley & Sons, Inc.
Chemical Elements
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Fundamental unit in chemistry
112 elements total
Use 1-2 letter symbols for each
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Examples: C= carbon, Na = sodium, Cl = chorine.
26 elements present in human body
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4 major ones (O, C, H, and N) make up 96%
8 others significant also. See Table 2.1.
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Atoms
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Smallest unit of an element that retains
characteristics of an element
Atom contains
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Total charge is neutral:
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Nucleus that has protons (+), neutrons (0)
Electrons (–) surrounding nucleus
Protons # = electron #
Atomic number = number of protons = number of
electrons
Mass number = number of protons + number of
neutrons
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Ions, Molecules and Compounds
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When an atom gives up of gains an electron,
it becomes an ion
When atoms share electrons, they form a
molecule
Two or more different atoms held together
with chemical bonds = a compound
Described by the molecular formula
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Molecular Formula
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O2 = oxygen
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Molecule: has 2 atoms bound together
H2O = water
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Molecule has 2 atoms bound together
Compound has 2 different atoms:
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H (hydrogen): 2 atoms
O (oxygen): 1 atom
Subscript indicates # of atoms of element
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Molecules
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Chemical Bonding
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Attraction between atoms to form
attachments
Electrons are grouped into shells
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Number of electrons in outer shell determines
type of bonding
Types of bonds:
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Ionic
Covalent
Hydrogen
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Ionic Bonds
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Electron is donated or accepted from another
atom  ion
Typically occurs between atoms in which:
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Electrons are negative (–) so:
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One has just 1 or 2 electrons in outer shells
Other has almost full outer shell (6 or 7 electrons)
If electron is accepted, atom  negative ion:
anion
If electron is donated, atom  positive ion: cation
Opposite charges attract  ionic bonding
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Ionic Bonds
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Covalent Bonds
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Sharing of electrons in outer shell  covalent
bonds
Typically occurs between atoms in which
outer shells are about half full.
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Example: bonds involving carbon (C) atoms (with
4 electrons in outer shell). These are organic
compounds.
Example: water
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Covalent Bonds
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Covalent Bonds
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Covalent Bonds
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Covalent Bonds
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Covalent Bonds
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Hydrogen Bonds
Form when a hydrogen atom (with a partial
positive charge) attracts the partial negative
charge of neighboring atoms, such as
oxygen or nitrogen.
Contribute strength and stability within large
complex molecules such as
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DNA
Proteins
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Chemical Reactions
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Occur when old bonds break and new bonds
form
Types:
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Synthesis
Decomposition
Exchange
Reversible
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Chemical Reactions: Synthesis
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Putting atoms together to form larger
molecules
A + B  AB
Example: 2H2 + O2  2 H2O
Synthesis in the body = anabolism
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Chemical Reactions: Decomposition
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Splitting molecules apart
AB  A + B
Example: CH4  C + 2H2
Decomposition in the body = catabolism
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Chemical Reactions: Exchange
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Involve both synthesis and decomposition
AB + CD  AD + BC
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Chemical Reactions: Reversible
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Can go in either direction: synthesis or
decomposition or exchange
Examples:
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A + B ↔ AB
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AB
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↔ A+B
AB + CD ↔ AD + BC
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Classes of Chemicals
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Inorganic
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Structure: lack C-H bonds; structurally simple
Examples
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Water, carbon dioxide, bicarbonate, acids, bases, and
salts
Organic
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Structure:
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All contain C-H bonds
Structurally complex (include polymers composed of
many units = monomers)
Classes: carbohydrates, lipids, proteins, nucleic acids
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Inorganic Compounds: Water
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Characteristics of water
Most abundant chemical in human body
 Good solvent and lubricant
 Takes part in chemical reactions
 Absorbs and releases heat slowly; regulates
body temperature
 Involved in digestion, circulation, and
elimination of wastes
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Acids, Bases and Salts
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Acid dissolves  H+ (1 or more)
Base dissolves  OH- (1 or more)
Acid + base  salt
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Example: HCl + NaOH  NaCl + H2O
acid + base  salt + H2O
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pH Concept
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The concentration of H+ or OH– expressed on
the pH scale
pH scale: 0–14
pH 7.0: H+ concentration = OH– concentration
pH < 7.0 = more H+ (acid)
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The smaller the number, the more H+
pH > 7.0 = more OH– (alkaline)
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The larger the number, the more OH–
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Organic Compounds
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Structure
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All contain C-H bonds
Structurally complex (include polymers composed
of many units = monomers)
Classes
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Carbohydrates
Lipids
Proteins
Nucleic acids
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Carbohydrates
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Most common sources of energy for humans
Three major classes: mono-, di-, poly
Monosaccharide: simple sugar. Common examples:
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Glucose (blood sugar) and fructose (fruit sugar)
Disaccharides: two bonded monosaccharides
Larger carbohydrates formed by dehydration
synthesis and broken down by hydrolysis
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↔ sucrose (table sugar)
Glucose + galactose ↔ lactose (milk sugar)
Glucose + glucose ↔ maltose
Glucose + fructose
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Carbohydrates
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Polysaccharides
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Monosaccharides (monomers) in long chains
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Complex branching structures not usually soluble
in water
Examples
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Glycogen: carbohydrate stored in animals (liver,
muscles)
Starch: carbohydrate stored in plants (potatoes,
rice, grains)
Cellulose: plant polymer (indigestible fibers)
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Polysaccharides
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Lipids
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Characteristics
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Insoluble in water = hydrophobic
Functions: protect, insulate, provide energy
Classes
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Triglycerides
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Most plentiful in diet and body
Each composed of 3 fatty acids + 1 glycerol
May be saturated, monounsaturated, or
polyunsaturated
Phospholipids: form lipid bilayer in membranes
Steroids based on ring-structure of cholesterol
Fat-soluble vitamins: A, D, E, and K
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Lipids: Triglycerides
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Lipids: Phospholipids
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Lipids: Steroids
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Cholesterol
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Ring structures similar to cholesterol
Used to make steroid hormones
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Estrogen, testosterone, cortisone
Help make plasma membranes stiff
Made in liver
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Proteins
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Structure: composed of amino acids (monomers)
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Amino acid structure: central carbon with
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20 different amino acids (like alphabet)
Acid (carboxyl) group (COOH)
Amino group (NH2)
Side chain (varies among the 20 amino acids)
Amino acids joined in long chains
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By dehydration synthesis to form peptide bonds 
dipeptide  tripeptide  polypeptide
Ultimately, form large, complex structures
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Amino Acids
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Proteins
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Functions (many)
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Much of cell structure
Contraction: muscle fibers
Regulate body: hormones
Transport of O2 in blood: hemoglobin
Defense: antibodies
Chemical catalysts: enzymes
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Enzymes
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Proteins that serve as chemical catalysts
Highly specific: one enzyme works on a
specific substrate  product
Efficient: one enzyme used over and over
Names
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Most end in “-ase”
Many give clues to functions: sucrase, lipase,
protease, dehydrogenase
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Enzymes
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Nucleic Acids
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DNA or RNA
Huge polymers composed of nucleotides
Each nucleotide (monomer) consists of
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Sugar (5-C monosaccharide: ribose or
deoxyribose)
Phosphate
Nitrogen-containing (nitrogeneous) base
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In DNA: adenine (A), guanine (G), cytosine (C), or
thymine (T)
In RNA: adenine (A), guanine (G), cytosine (C), or
uracil (U) (which replaces T of DNA)
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DNA Molecule
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Nucleic Acids: DNA
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Nucleotides are connected into long chains
that are bonded by bases:
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C – G, G – C, T – A, or A – T
Two chains form double helix (spiral ladder)
Function: stores DNA (genetic information) in
genes (found in chromosomes) that:
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Direct protein synthesis and therefore regulate
everyday activities of cells
Carry this genetic information to the next
generation of cells
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Nucleic Acid: RNA
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Nucleotides are connected into a long, single
chain (one side of a ladder)
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In transcription, RNA (italics) positions next to
DNA: C – G, G – C, A - T, or U – A
In translation, t-RNA (italics) positions next to mRNA (italics): C – G, G – C, A - U, or U - A
Function:
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Carries out protein synthesis by correctly
sequencing amino acids, so helps to regulate
everyday activities of cells
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ATP
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Structure: composed of chemicals similar to
those in RNA: base (adenine), ribose, and
phosphates
Function: the main energy-storing molecule in
the body
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ATP contains 3 phosphates
Carries energy in high-energy chemical bonds
between terminal phosphate groups
Energy released from those bonds when they
break: ATP  ADP + phosphate + energy
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Structure of ATP and ADP
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End of Chapter 2
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