Chemical Basis of Life

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Chapter 4

• Chemical Basis of Life

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4.1 Elements of Life

• Objectives
• List the most common elements in living things
• Compare and contrast elements and compounds

• Vocab
• Matter Element
• Trace element Compound

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4.1 Elements of Life

• Matter anything that occupies space has mass
  (stuff)
• Elements matter composed of only one type of
  atom pure substance cannot be broken down by
  chemical means.
• Periodic Table Menu of elements

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4.1 Elements of Life

• Elements essential for life C H O N
• Oxygen (65)
• Carbon (18.5)
• Hydrogen (9.5)
• Nitrogen (3.3)
• Trace Elements (Less than 0.01) - small amounts
  needed but important for proper function
• Calcium, Phosphorous, Potassium, Sulfur, Sodium,
  Chlorine, Magnesium

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An Element

• Elements of the Periodic Table
• They are represented by a one or two letter
  symbol on the periodic table.
• Atomic protons
• Atomic mass mass of nucleus (p n)

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4.2 Atomic Structure

• Structure

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The Atom Basic unit of matterSubatomic Particles

• Proton, Neutron Electron
• 1. Proton () defines the atom)
• 2. Neutron no charge
• 3. Electron (-) almost no mass (so little we
  ignore it)
• Electrons are not found in the nucleus
• They travel at high speeds throughout the atom in
  a series of distinct energy levels that surround
  the nucleus.
• Electron cloud Refers to all the possible
  locations that an electron could be.

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Electron Cloud Model
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Electron Energy Levels

• Electrons orbit the nucleus at different
  distances, or Energy LEVELS.
• Bigger distance more energy
• 1st Energy Level fits 2 electrons (K)
• 2nd Energy Level fits 8 electrons (L)
• 3rd Energy Level fits 18 electrons (M) 8 act
  as valence
• 4th Energy Level fits 32 electrons (N)

Note electrons do not really move in perfect
circles like this.
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VALENCE ELECTRONS

• Electrons in outer most energy level that are
  available for bonding.
• Atoms want to have the MAX. of VALENCE
  ELECTRONS for stability.
• valence determines chemical bonding
  reactivity.
• If an atom already has the max of valence
  electrons, it wont form bonds

MAX. VALENCE 1st energy level 2 electrons 2nd
energy level 8 electrons 3rd energy level 8
electrons
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What Is An Isotope?

• The number of protons will never change, but the
  number of neutrons can vary from atom to the
  next.
• Isotopes of an atom differ in neutron number.
• ( Protons ? neutrons)

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Radioisotopes

• Some larger isotopes are unstable and decay
  giving off radiation (matter energy)
• Such isotopes are useful in research and medicine
• Biological spies for body scans
• Radiation treatment for cancer

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Radioactive Isotopes P.E.T. scan
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4.3 Chemical Compounds

• Produced when elements combine to form substances
  consisting of two or more different atoms.
• Represented by chemical formulas
• Water (H2O), Table Salt (NaCl), Sulfuric Acid
  (H2SO4)

Multiple Molecules
Single Molecule
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4.3 Forming Bonds Share or Transfer Electrons

• In order to achieve stability an atom will
  either transfer or share electrons (valence)
• This is achieved through either ionic or covalent
  bonding.
• Watch http//www.youtube.com/watch?vQqjcCvzWwww
  featurerelated
• http//www.youtube.com/watch?NR1vLRVW0tgSLRI

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Ionic Bonding

• Ionic bonding involves the transfer of
  electrons from one atom to another (gain or
  lose).
• Ex NaCl
• THIS IS HOW SALTS ARE MADE.

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Covalent Bonding in Molecules

• chemical bond formed by the sharing of electrons.
  
• No elements are gaining or losing atoms.
• Ex. H20

1 covalent bond 1 pair of shared valence
electrons
Structural formula model
Space filling model
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Covalent Bonding Single Bond

• Every shared valence electron forms a covalent
  bond holding the molecule together.
• Single Bond (Share 1 pair v.e.)

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Covalent Bonding Double Triple Bonds

• Double Bond (Share 2 pair v.e.)

• Triple Bond (Share 3 pair v.e.)

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• Bonding Prompt
• The number of bonds that an atom can form depends
  on the atoms valence electrons (Remember 2, 8,
  8).
• Keeping this in mind, identify the maximum number
  of bonds that can be formed by each of the
  following elements
• a). H b). C c). O d). N e).
  He
• B. Long complex molecules would probably be made
  up of _________ atoms. (Based on answer to part
  A).

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Chemical Reactions

• During chemical reactions, the chemical bonds of
  the REACTANTS (starting materials) are broken
  atoms are rearranged , and new bonds are formed
  in the PRODUCTS (end materials). Products have
  new properties.

REACTANTS
PRODUCTS
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Chemical Reactions Law of Conservation of Mass

• During chemical reactions, no matter (atoms) can
  be lost or gained. Atoms are just rearranged.

Coefficients of molecules
REACTANTS
PRODUCTS
Subscript atoms in molecule
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• Bonding Summary
• Covalent bond? Ionic bond? Hydrogen bond? Polar
  covalent? Non-polar?
• Hold elements in a compound together __________
• Based on attraction between oppositely charged
  ions __
• Bonds that form salts, like NaCl ____
• Strong bonds formed by sharing electrons ____
• Covalent bonds in which electrons are not equally
  shared results in partially charged molecules
  ____________
• Atoms of H and O in water are held together by
  these _______
• Individual water molecules are attracted to one
  another by these ________

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CH. 4.3 Chemistry of Water

• One of the few naturally occurring
• compounds that is liquid at the temperatures
  found on the Earths surface.
• Living organisms are 70 - 95 water

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Water A Polar Molecule

• Some molecules have an uneven distribution of
  electrons
• Since Oxygen is a bigger atom (more protons) than
  the hydrogen atoms, the electrons spend more time
  near the oxygen
• This creates a partial charge on each end
• Polar molecules have charged ends (like a
  magnets polarity)
• Overall the molecule is neutral (no charge)

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Water Hydrogen Bonds

• Because of their partial positive negative
  charges, polar molecules like water can attract
  each other.
• The hydrogen atom of one water being attracted to
  the oxygen atom of another water is an example of
  hydrogen bonding.

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Properties of Water Water is a SOLVENT

• Water is an excellent SOLVENT (It dissolves
  things).
• Things that dissolve(salts, sugar) SOLUTES.
• The partial charges in water (POLARITY) attract
  the charges in other substances this pulls them
  apart (DISSOLVE)
• Polar molecules and salts dissolve in water. Non
  polar substances (oil, etc. do not dissolve)
• Importance
• Water is main solvent in cells, blood, etc.
• Dissolved substances are transported by blood and
  lymph

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• Properties of Water Moderate Temperature Change
• High Heat Capacity resists change in
  temperature (a lot of energy stored/released for
  temp change)
• High Heat of Vaporization evaporation requires
  a lot of energy water stays a liquid on Earth
• Both of these properties are due to H-bonding of
  water.
• When warming up water, absorbed energy is used to
  BREAK H-BONDS then temps. can change.
• When temps. decrease H-Bonds form. This
  releases energy and keeps temps from dropping
  rapidly.
• Results Oceans absorb release heat slowly,
  preventing rapid climate/temp. change!

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Properties of Water Cohesion, Adhesion
Capillary Action

• Cohesion attraction (by H-bonding) between two
  molecules of the same polar substance (Water
  sticks to itself beads up)
• Adhesion attraction (by H-bonding) between two
  molecules of the different polar substances
  (Water sticks to other things wets them).
• Capillary Action Water moves up a tube b/c it
  is attracted to the sides.

Water moves from roots to shoots in trees. Water
is attracted to walls of xylem (tubes of tissue
analogous to our veins) by ADHESION. Water
molecules pull each other along COHESION
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Surface Tension
Film-like surface of water due to cohesion at
the surface.
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Solutions

• Solution a homogenous mixture in which one
  substance is dissolved into another
• A solute (like sugar) completely dissolves in a
  solvent (like water) like in iced tea.
• Water is the best (universal) solvent due to its
  polarity (charged ends)
• Blood is mostly water. Bloods job distribute
  dissolved substances throughout body.

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Water acts like a magnet.
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Suspensions

• Materials do not break up into individual atoms,
  but particles are small enough that they do not
  settle on the bottom of a container.
• Example blood

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Solutions Acids

• When some compounds dissolve
• in water, they break apart into
• individual ions.
• HCl ? H Cl-
• Compounds that release hydrogen ions (H) into a
  solution are acids High H
• means concentration of
• Characteristics of Acids (do not write)
• Produce H (H3O) ions in water
• Taste sour
• Corrode metals
• React with bases to form salts and water
• Are electrolytes

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Solution Bases

• Bases are compounds that release
• hydroxide ions (OH-) into a solution
• NaOH ? Na OH-
• Produce OH- ions in water or pick up/remove H
  ions
• Characteristics of Bases (do not write)
• Taste bitter, chalky
• Are electrolytes (produce electricity)
• Feel soapy, slippery
• React with acids to form salts and water

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• pH Scale measure how acidic or basic a solution
  is.
• 7 is a neutral pH
• H OH-
• pH lt 7 acid (high concentration H)
• pH gt 7 base (low concentration H)
• Farther pH from 7, the more acidic or basic
• Every change in pH value corresponds to a
  ten-fold change in H
• pH 3 is 10x more acidic than pH 4 and 100x more
  acidic than pH 5

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pH Self Assessment

• Strong acid? Weak acid? Neutral? Weak base?
  Strong base?
• High H?
• High pH ?
• H OH-?

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Buffers

• Substances that resist changes in pH.
• Important in living organisms where change in pH
  can be deadly (Blood contains bicarbonate ion
  buffers)
• When pH drops, buffers remove Hions
• When pH rises, buffers add H ions
• Helps to maintain homeostasis

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Water Molecule Models

• 1. Red circle ____ White circle _______
• Sketch water molecule. Label () and (-) ends.
• Explain WHY water has a () and (-) end.
• Sketch how water molecules attract other water
  molecules. Label the hydrogen bond in your
  drawing.
• Is ethane (C2H6) polar or non polar? Provide a
  reason.
• Which end of a water molecule would be attracted
  to an Na ion?

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