Chapter%202%20The%20Nature%20of%20Molecules

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• Chapter 2The Nature of Molecules

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Comment

• Much of this chapter should be review from a
  basic chemistry course. Much of the material is
  unlikely to be brand new.

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Matter

• Anything that has mass and occupies space.

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Atoms

• Smallest particle of elements.

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Element

• Matter made up of only one type of atom.
• 92 natural elements.
• Each element has a symbol.

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Compound

• Elements combined in fixed ratios.
• A compound has characteristics beyond those of
  its combined elements.

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Question?

• What Elements are necessary For Life?
• Life requires about 25 chemical elements.

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Macroelements

• Elements needed in large amounts or quantities.
• Examples
• C HOPKNS CaFe Mg NaCl

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Control
Minus Nitrogen
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Microelements

• Elements needed in very small quantities.
• Also known as Trace Elements.
• Examples
• Cu, Co, Zn, Mo, I, Mn

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Goiter minus Iodine
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Atomic Number

• The number of protons in the nucleus.
• Each element has its own atomic number. If you
  change the atomic number, you no longer have the
  same element.

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Atomic Mass

• The number of protons and neutrons in the
  nucleus.
• The atomic mass can change.

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Atomic Model
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Isotopes

• Atoms of the same (iso-) element with different
  atomic mass.
• Caused by changes in the number of neutrons.
• Used as tracers.

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Types of Isotopes

• 1. Radioactive
• - where the nucleus decays spontaneously, giving
  off particles and energy.
• 2. Heavy
• - has a stable nucleus, but masses more than the
  standard isotope for the element.

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Energy

• The ability to do work.

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Potential Energy

• Is the energy that matter stores because of its
  position or location.
• Electrons have potential energy because of their
  position relative to the nucleus.

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Electron Energy Levels

• Energy levels around the nucleus of an atom.
• 1st level can have 2 electrons and has the lowest
  potential energy.
• Other levels can hold more than 2 electrons and
  have higher energy levels.

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Electron Orbitals

• The three dimensional space where an electron is
  found 90 of the time.
• Different orbitals have different shapes.
• Each orbital can hold only 2 electrons.

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Electron Orbitals
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Chemical Behavior Of An Atom

• Is determined by its electron configuration in
  the energy levels and orbitals.

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Valence Electrons

• The electrons in the outermost energy level.
• Electrons available chemical bonds.

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Octet Rule

• The most stable condition is to have an outer
  level of 8 electrons.
• Exception - 1st level is stable with only 2
  electrons.
• When stable - no chemical reactions will take
  place. Ex Ne, He, (Noble gases)

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Electrons of the first elements
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Chemical Bonds

• Forces that join atoms together to form
  molecules.
• Usually caused by sharing or transferring valence
  electrons.

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Bond Formation Depends On

• The number of valence electrons that must be
  gained, lost, or shared to reach the stable
  condition.

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Chemical Bond Types

• Nonpolar Covalent
• Polar Covalent
• Ionic
• Hydrogen

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Nonpolar Covalent

• When electrons are shared equally between atoms.
• Very strong bond.
• Important in many molecules found in living
  things. Ex carbon to hydrogen

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Nonpolar Covalent

• Can be single, double, or triple between two
  atoms.
• Each nonpolar covalent bond involves a pair of
  electrons.

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Polar Covalent

• When electrons are shared unequally between
  atoms.
• Results in polar molecules that have charged
  areas. Ex Water, H to O bonds

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Ionic Bonds

• Formed when electrons are transferred from one
  atom to another and ions are formed.

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Types of Ions

• Cations - have lost electrons (p gt e-) giving
  them a positive charge.
• Anions - have gained electrons (p lt e-)
  giving them a negative charge.

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Ionic Bonds

• Formed when cations and anions attract each
  other.
• Weak chemical bond.

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Lilli Ashmore
The Indiana Academy for Science, Mathematics and
Humanities
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Ionic Bonds
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Hydrogen Bonds

• When a hydrogen atom bonded to one molecule is
  attracted to the slightly negative area (often N
  or O) of another molecule.
• Very weak individual bond.
• Can be a strong force if there are many H
  bonds.

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Hydrogen Bonds
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Molecular Shape

• Determined by the positions of the atoms
  orbitals.
• Molecular shape is crucial in Biology because it
  determines how most molecules of life recognize
  and respond to one another.

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Chemical Reactions

• The making and breaking of chemical bonds.
• Reactions do not destroy matter, they only
  rearrange it.

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Parts of the Equation

• 2 H2 O2 2 H2O
• Reactants
• - the starting materials.
• Products
• - the ending materials.
• Note - all atoms of the reactants must be
  accounted for in the products.

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Chemical Equilibrium

• When the conversion of reactants to products is
  balanced to the reverse reaction.
• Ex
• 3 H2 N2 2 NH3

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Summary

• Element vs compound
• Macro and micro elements
• Atomic Number and Mass
• Isotopes
• Valence electrons
• Chemical Bonds

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Summary

• We will now put elements together to form
  molecules and build the next level in the
  hierarchy.

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Should we control a chemical that

• Causes excessive sweating and vomiting.
• Is a major component in acid rain.
• Can cause severe burns in its gaseous state.

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• Accidental inhalation can kill you.
• Contributes to erosion.
• Decreases the effectiveness of car brakes.
• Has been found in tumors of terminal cancer
  patients.

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What is the chemical?

• Dihydrogen monoxide
• Otherwise known as H2O

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Question?

• What molecule Is the most common In living Cells?
• Water - most cells are 70 - 95
  
  water.

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The Water Planet
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Properties Of Water

• Be ready and able to discuss several of the
  following properties.
• Focus on definitions and examples.
• Review water structure and H-bonds

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Liquid Water Is Cohesive

• Water sticks to water.
• Why?
• Because the polarity of water results in
  hydrogen bonding.

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Liquid Water is Adhesive

• Water sticks to other molecules.
• Why?
• Hydrogen bonding.

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Water transport in trees uses Cohesion and
Adhesion
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Water Has A High Surface Tension

• The surface of water is difficult to stretch or
  break.
• Why? Hydrogen bonding.

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Water Has A High Specific Heat

• Specific Heat - the amount of heat needed to
  raise 1 g of the substance 1 degree C.
• Why?
• Hydrogen bonding.

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Heat

• Total quantity of kinetic energy due to molecular
  motion.

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Temperature

• Measures the average speed of the molecules.

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Celsius Scale

• Will be used for most of our temperature
  measurements.
• O oC - water freezes
• 100 oC - water boils
• 37 oC - human body
  

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Water Stabilizes Temperature

• Water can absorb and store a huge amount of heat
  from the sun.
• Result - climate moderation
• Result - organisms are able to survive
  temperature changes.

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Water Has A High Heat Of Vaporization

• Heat of Vaporization the quantity of
  heat a liquid must absorb for 1g of it to convert
  to a gaseous state.

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Evaporative Cooling
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Result

• Water cools organisms from excessive heat
  buildup.
• Why?
• Hydrogen bonding

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Water Expands When It Freezes

• The distance between water molecules INCREASES
  from the liquid to the solid form.
• Why?
• Hydrogen bonding

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Solids and Liquids
Water
Benzene
Floats
Sinks
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States of Matter
Liquid
Gas
Solid
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Result

• Aquatic life can live under ice.

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Water Is A Versatile Solvent

• Water will form a solution with many materials.
• Why?
• Hydrogen bonding

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Solution

• Homogeneous mixture of two or more substances.

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Solvent

• The dissolving agent.
• The material in the greater quantity.

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Solute

• The substance that is dissolved.
• The material in the lesser quantity.

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Hydrophilic Materials

• Materials that dissolve in water.
• Hydro - water
• philic - to like or love
• Have ionic or polar regions (polar covalent
  bonds) on their molecules for H bonds.

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Hydrophobic

• Materials that repel water.
• Hydro - water
• phobic - to fear
• Have non-polar covalent bonds. Ex - lipids.

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Without Water Life Would Not Be Possible!!
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Solution Concentration

• Usually based on Molarity.
• Molarity - the number of moles of solute per
  liter of solution.

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Moles

• The molecular weight of a substance in grams.
• One Avogadros number of molecules.
• 6.02 X 1023

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One Mole of each
Sugar
Copper Sulfate
Sulfur
Mercury Oxide
Sodium Chloride
Copper
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Comment

• AP Biology students should be able to calculate
  solutions in Molarity.

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Dissociation of Water

• Water can sometimes split into two ions.
• In pure water the concentration of each ion is
  10-7 M

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• Adding certain solutes disrupts the balance
  between the two ions.
• The two ions are very reactive and can
  drastically affect a cell.

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Acids

• Materials that can release H
• Example HCl
• HCl H Cl-

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Acid Rain
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Acid Rain
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Bases

• Materials that can absorb H
• Often reduce H by producing OH-
• Example NaOH
• NaOH Na OH-

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Neutrals

• Materials that are neither acids nor bases.

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pH Scale

• A logarithmic scale for showing H concentration
• pH - log H

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pH Scale
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Example

• For a neutral solution
• H is 10-7
• or - log 10-7
• or - (-7)
• or 7

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• Acids pH lt7 etc.
• Bases pH gt7 etc.
• Each pH unit is a 10x change in H

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Comment

• H OH- 14
• Therefore, if you know the concentration of one
  ion, you can easily calculate the other.

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Buffers

• Materials that have both acid and base
  properties.
• Resist pH shifts.
• Cells and other biological solutions often
  contain buffers to prevent damage.

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Summary

• Be able to discuss the properties of water.
• Be able to measure solution concentrations in
  Molarity.
• Be able to work pH scale questions.