The Chemistry of Life Chapter 2

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The Chemistry of LifeChapter 2
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Why should we study chemistry in
Biology?
Life depends on chemistry!
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Life depends on chemistry!

• When you eat food or inhale oxygen, your body
  uses these materials in chemical reactions that
  keep you alive.
• Just as buildings are made from bricks, steel,
  glass, and wood, living things are made from
  chemical compounds.
• Wouldnt you want an architect to understand
  building materials? Same idea applies to
  geneticists, ecologists, zoologists, botanists,
  biologists, and etc.

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Atoms

• The study of chemistry begins with the basic unit
  of matterthe
• History
• Greeks were first to try to explain chemical
  reactions
• 400 BC thought all matter composed of
• Fire
• Earth
• Water
• Air
• Democritus first used word atomos, meaning
  indivisible

Atom
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Atoms

• Atoms are composed of 3 main particles
  (subatomic particles)
• Protons ()
• Neutrons
• Electrons (-)

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Protons and Neutrons

• Strong forces bind protons and neutrons together
  to form the nucleus, which is at the center of
  the atom.
• Both particles have about the same mass.

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Electrons

• Electrons are negatively charged with about
  1/1840 the mass of a proton.
• They are in constant motion in the space
  surrounding the nucleus.

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Atoms

• Atoms have equal numbers of electrons and
  protons.
• Because these subatomic particles have equal but
  opposite charges, atoms are neutral.

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Elements

• Elements are the building blocks of all matter.
• Elements cannot be decomposed into simpler matter.

Group Number 1 2
3 4 5 6 7 8
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The Elements

• 110 known elements
• 88 occur naturally

The 110 elements form a plethora of compounds,
just as 26 letters of the alphabet make a
seemingly endless number of words.
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Atomic Number

• Counts the number
• of
• protons
• in an atom

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Atomic Number on the Periodic Table
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All atoms of an element have the same number of
protons
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Atomic Mass

• Mass of an atom.
• Approximately equal to the number of protons and
  neutrons
• Find number of neutrons by subtracting the number
  of protons from the mass.

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Review

• An element's atomic number tells how many protons
  are in its atoms.
• An element's mass number tells how many protons
  and neutrons are in its atoms.

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Learning Check 1

• State the number of protons for atoms of each
  of the following
• A. Nitrogen
• 1) 5 protons 2) 7 protons 3) 14
  protons
• B. Sulfur
• 1) 32 protons 2) 16 protons 3) 6
  protons
• C. Barium
• 1) 137 protons 2) 81 protons 3) 56
  protons

2) 7 protons
2) 16 protons
3) 56 protons
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The Periodic Table
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Isotopes

• Isotopes are atoms that have the same atomic
  number but different mass number.
• Most elements have two or more isotopes.
• Same chemical properties because the electron
  number does not change.

What does that mean?
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Isotope symbols
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Example

• Is the 5 necessary ?

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More about isotopes

• Some isotopes have unstable nuclei which break
  down over time.
• They are called radioactive isotopes
• Some radiation is harmful.

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• Radiation can also be useful

Radioactive Dating
Tracers with X-rays
Cancer Treatment
Kill bacteria
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More About Atomic Structure

• The center of the atom is called the nucleus.
• Electrons live in something called shells.
• Shells are areas that surround the center of an
  atom.
• A shell is sometimes called an orbital or energy
  level.

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More About Electrons

• Every shell can hold only so many electrons
• The further from the nucleus, the more electrons
  a shell can hold

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Valence Electrons

• The electrons on the outside edge of the atom
• This is where the action is- where bonding takes
  place
• Atoms have no more than 8 valence electrons

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Energy Level (Shell) Maximum Number of Electrons Max number of Valence Electrons
1 2 2
2 8 8
3 18 8
4 32 8
5 50 8
6 72 8
7 98 8
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The Octet Rule

• Atoms will combine to form compounds in order to
  reach eight electrons in their outer energy
  level. This is very stable!
• Atoms with less than 4 electrons tend to lose
  electrons.

• Atoms with more than 4 electrons tend to gain
  electrons.

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Compound

• Two or more elements chemically combined in
  specific proportions
• Examples
• Water H2O
• Salt NaCl
• Sugar C6H12O6

• Two types of compounds
• Ionic
• Covalent

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Ionic Compounds

• Form when electrons are transferred from one atom
  to another.
• Ions - Atoms with a net charge due to gaining or
  losing electrons
• Gaining electrons gives an ion a negative charge
• Losing electrons gives an ion a positive charge
• If they have to choose, atoms would
  rather be stable (with a full octet) than
  neutral.

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How Does This Happen?
Some atoms have a few too many electrons
Some atoms only need a few electrons
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What do you do if you are a sodium (Na) atom
with one extra electron?

• Go look for an atom that wants it!

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Ionic Bonding

• Negative ions and positive ions are held together
  by ionic bond.

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• Ionic compounds form between metals and nonmetals

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What If No One Will Give Up An Electron?

• Atoms with less than 8 valence electrons can move
  close to each other and share their electrons
• The electrons spend their time around both atoms.
• And they lived happily ever after!

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Covalent Bonds

• Formed when a pair of electrons is shared between
  two atoms.
• Sometimes the atoms share two pairs of electrons
  and form a double bond, or three pairs of
  electrons to form a triple bond.
• Structures formed by
• covalent bonds are
• molecules.

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• Covalent compounds form between 2 nonmetals

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Van der Waals Forces

• There are small attractive forces between all
  atoms
• Help to hold molecules to each other
• Ex Gecko

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Why do compounds form?
Lets summarize what we know!

• Atoms are trying to get 8 valence electrons

How do compounds form?

• By ionic (e- transfer) or covalent (e- sharing)
  bonding

How can you tell if a compound is ionic or
covalent?

• By the types of elements in the compound (ionic
  M M covalent M NM)

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Learning Check 2
Indicate whether a bond between the following
would be 1) Ionic 2) covalent ___ A. sodium
and oxygen ___ B. nitrogen and oxygen
___ C. phosphorus and chlorine ___ D.
calcium and sulfur ___ E. chlorine and
bromine
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2-2 Water is a Polar Molecule

• Polar Molecule in which electrons are shared
  unevenly between atoms, causing each end of the
  molecule to have a slight charge

Negative end
Positive end
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• This causes water to be attracted to other polar
  or charged particles
• Water is attracted to ions
• Water is attracted to itself, forming hydrogen
  bonds

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Hydrogen Bonds In Water Are Responsible For

• Adhesion
• Attraction between molecules of different
  substances
• Graduated cylinder
• Cohesion
• Attraction between molecules of the same
  substance
• Drops of water on a penny
• Ex Surface Tension
• Jesus Lizard

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Types of Chemical Substances

• Compounds and Elements are called pure
  substances.
• Most matter is neither of these.

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Mixtures

• Mixtures are combinations of substances held
  together by physical forces, not chemical bonds.
• Each substance keeps its own properties

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Mixtures may be either

• Solutions

• Colloids

• Suspensions

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Solutions

• Have small particles
• Are transparent (not the same as colorless)
• Do not separate
• Water solutions are very common in biological
  systems
• Examples salt water, kool-aid, air, brass,
  vinegar

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Colloids

• Have medium size particles
• Do not separate
• Examples fog, whipped cream, milk, cheese,
  mayonnaise

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Suspensions

• Have very large particles
• Settle out (separates into layers)
• Examples blood platelets, muddy water, calamine
  lotion, oil water, Italian salad dressing

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pH Scale

• Measures concentration of hydrogen ions in a
  solution
• Ranges from 0 to 14
• 7 is neutral
• 0-7 have more hydrogen ions (H) and are acidic
• 7-14 have more hydroxide ions (OH-) and are basic

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Acids, Bases, and pH

• Water molecules form ions
• H2O H OH-
• Water hydrogen ion hydroxide ion
• Very few ions are formed in pure water, but there
  are equal numbers of hydrogen and hydroxide ions
• Water is neutral!

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pH of common substances
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pH and Homeostasis

• Maintaining a pH between 6.5 and 7.5 is important
  in cells
• Dissolved compounds called buffers control pH
• Proteins
• Phosphates
• Hydrogen carbonate

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Chemical Reactions

• When one set of chemicals changes into another
  set of chemicals, a chemical reaction occurs
• Bonds are either broken or formed (or both!)

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Chemical Equations

• Represent a reaction
• Give the types and amounts of substances that
  react and form
• Reactants Products
• 2H2 O2

yields
yields
2H2O
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Evidence of a Chemical Reaction

• Formation of a precipitate (a solid substance
  separated from a liquid)
• Gas is evolved (seen by bubbles forming in a
  liquid)
• Change in heat or light energy

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Organic Compounds
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Organic Compounds

• Make up most of living organisms
• Contain bonds between two or more carbon atoms
• C can easily bond with up to 4 other elements

4 valence electrons 4 covalent bonds
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Organic Compounds

• Carbon atom is versatile, can be backbone of
  long chains or rings
• Organic molecules can be extremely large and
  complex these are called macromolecules

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Organic Compounds

• Four main types of organic macromolecules
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

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Carbohydrates

• Made of C, H, O
• Main energy source for living things
• Breakdown of sugars supplies immediate energy for
  cell activities
• Extra sugar is stored as complex carbs called
  starches

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Carbohydrates

• Single sugar molecules are called monosaccharides
• Examples
• glucose in many plant and animal tissues, most
  common monosaccharide
• fructose in many fruits
• galactose component of milk

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Carbohydrates

• Large molecules of many monosaccharide are
  polysaccharides
• Examples
• glycogen animals use to store excess sugar
• plant starch plants use to store excess sugar
• cellulose fibers that give plants their
  rigidity strength

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Lipids

• Store more energy than CHOs because the chains
  are longer
• Ex Fats, oils, waxes
• Wont dissolve in water

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Lipids

• Important parts of biological membranes and
  waterproof coverings
• Steroids are lipids that act as chemical
  messengers

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Lipids

• Many lipids are made from a glycerol combined
  with fatty acids
• If all carbons have single bonds, lipid is
  saturated
• Ex butter, lard, animal fat (usually solid at
  room temperature)
• If any carbons have double or triple bonds, lipid
  is unsaturated
• Ex vegetable oil, fish oil, peanut oil (usually
  liquid at room temperature)

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Proteins

• Contain C, H, O, plus nitrogen
• Formed from amino acids joined together
• More than 20 amino acids can be joined in any
  order or number to make countless proteins (think
  of how many words can be made from 26 letters!)

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Proteins

• Chains are folded and twisted giving each protein
  a unique shape
• Van der Waals forces and hydrogen bonds help
  maintain proteins shape
• Shape of protein is important to its function!

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Proteins

• Provide structure
• Ex Collagen- makes up your skin, muscles
  bones
• Aid chemical activities in your body
• Ex Enzymes- work to speed up rxns in
  your body
• Transport substances into or out of cells
• Help fight diseases

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Nucleic Acids

• Contain C, H, O, N plus phosphorus
• Formed by bonding of individual units called
  nucleotides

Nucleic Acid
nucleotide
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Nucleic Acids

• Store and transmit hereditary information
• Ex DNA (deoxyribonucleic acid)
• RNA (ribonucleic acid)

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