Chapter 2 The Chemical Context of Life

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Chapter 2The Chemical Context of Life

• AP Minknow
• The three subatomic particles and their
  significance.
• The types of bonds, how they form, and their
  relative strengths

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Overview

• Living organisms and the world they live in are
  subject to the basic laws of physics and
  chemistry.
• Biology is a multidisciplinary science, drawing
  on insights from other sciences.
• Life can be organized into a hierarchy of
  structural levels.
• At each successive level, additional emergent
  properties appear.

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2.1 Matter consists of chemical elements in pure
form and in combinations called compounds.

• Organisms are composed of matter.
• Matter is anything that takes up space and has
  mass.
• Matter is made up of elements.

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2.1 Matter consists of chemical elements in pure
form and in combinations called compounds.

• An element is a pure substance that cannot be
  broken down into other substances by chemical
  reactions.
• There are 92 naturally occurring elements.
• Each element has a unique symbol, usually the
  first one or two letters of the name. Some of the
  symbols are derived from Latin or German names.

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2.1 Matter consists of chemical elements in pure
form and in combinations called compounds.

• A compound is a pure substance consisting of two
  or more elements in a fixed ratio.
• Table salt (sodium chloride or NaCl) is a
  compound with equal numbers of atoms of the
  elements chlorine and sodium.

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Essential Elements of Life

• Essential elements
• Include carbon, hydrogen, oxygen, and nitrogen
• Make up 96 of living matter
• A few other elements
• Make up the remaining 4 of living matter

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Trace elements

• Are required by an organism in only minute
  quantities
• But the absence of trace element can have deadly
  effects

Figure 2.3
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2.2 An elements propertiesdepend on the
structure of its atoms

• An atom
• Is the smallest unit of matter that still retains
  the properties of an element
• Each element
• Consists of a certain kind of atom that is
  different from those of other elements
• Atoms differentiate themselves through the number
  and arrangement of their subatomic particles.
• Protons charge
• Neutrons no charge
• Electrons - charge

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2.1 What Are the Chemical Elements That Make Up
Living Organisms?

• Atoms have volume and mass.
• Mass of one proton or one neutron atomic mass
  unit (amu) or 1 dalton, or 1.7 1024 grams.
• Mass of one electron 9 1028usually ignored

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Simplified models of an atom
WARNING Conceptual Models NOT WHAT THEY LOOK
LIKE
Figure 2.4
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Question 1Create this table and fill in the
blanks.
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Questions 2-4

• 2. Which subatomic particle determines what type
  of element it will be?
• 3. Which subatomic particle plays the largest
  role in atomic interaction?
• 4. What is the difference between atomic mass and
  mass number?
• 5. What subatomic number can easily vary, but
  still have the same element?

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Isotopes
Isotopes forms of an element with different
numbers of neutrons, thus different mass
numbers Example 12C has 6 neutrons 13C has 7
neutrons 14C has 8 neutrons
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Radioactive Isotopes

• Spontaneously give off particles and energy
• Alpha, beta, gamma radiation

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Biological Uses for Radioactive Isotopes
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Figure 2.5
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PET(positron-emission tomography)
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Figure 2.4 Tagging the Brain
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Question 6 - 7

• 6. How are radioactive isotopes used in slide 17
  and 18?
• 7. How are radioactive isotopes used in carbon
  dating?

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Atoms and their electrons

• The number of electrons determines how atoms will
  interact.
• Chemical reactions involve changes in the
  distribution of electrons between atoms.
• An atoms electrons
• Vary in the amount of energy they possess

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The Energy Levels of Electrons

• Energy
• Is defined as the capacity to cause change
• Potential energy
• Is the energy that matter possesses because of
  its location or structure

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The Energy Levels of Electrons

• Energy levels
• Are represented by electron shells

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Electron Configuration and Chemical Properties

• The chemical behavior of an atom
• Is defined by its electron configuration and
  distribution

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Question 8

• 8. In an electron diagram of phosphorus, in
  which shell do electrons have the most potential
  energy? In which shell do electrons have the
  least potential energy?

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Electron Configuration and Chemical Properties

• Locations of electrons in an atom are described
  by orbitals.
• Orbital region where electron is found at least
  90 percent of the time.
• Orbitals have characteristic shapes and
  orientations, and can be occupied by two
  electrons.
• Orbitals are filled in a specific sequence.

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Electron Configuration and Chemical Properties

• Each electron shell
• Consists of a specific number of orbitals

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Electron Configuration and Chemical Properties

• Orbitals occur in series called electron shells
  or energy levels.
• First shell one orbitals orbital
• Second shell one s and three p orbitals (holds
  eight electrons)
• Third shell one s and three p orbitals (holds
  eight electrons)
• Fourth Fifth Shells d orbitals added (10 more
  electrons)
• Seventh Eighth Shells f orbitals added (16
  more electrons)

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Valance Shell Valance Electrons
Question 8 How many orbitals are found on the
valance shell of a Argon atom? Question 9 -
What orbitals are present? Question 10 How many
valance electrons does Argon have?
Sodium? Question 11 How does the differing
structures of an argon atom and a sodium atom
relate to their differing chemical interactions?
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Questions 9-12
9. How many orbitals are found on the valance
shell of a Argon atom? 10. What orbitals are
present? 11. How many valance electrons does
Argon have? Sodium? 12. How does the differing
structures of an argon atom and a sodium atom
relate to their differing chemical interactions?
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Electron Configuration and Chemical Properties

• Reactive atoms have unpaired electrons in their
  outermost shell.
• Atoms can share electrons, or loose or gain
  electrons, resulting in atoms bonded together to
  form molecules.
• The octet rule

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Electrons and Chemical Bonding

• Chemical bond attractive force that links atoms
  together to form molecules
• Covalent bonds atoms share one or more pairs of
  electrons, so that the outer shells are filled.

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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• Biological molecules are put together with
  covalent bonds and are very stable.
• Covalent bonds are very stronga lot of energy is
  required to break them.

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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.
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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• Orientation of bonds
• The length, angle, and direction of bonds
  between any two elements are always the same.
  (interactions can change them though)
• Example Methane always forms a tetrahedron.

methane tetrahedron here
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Covalent Bonds

• Covalent bonds can be
• Singlesharing one pair of electrons
• Doublesharing two pairs of electrons
• Triplesharing three pairs of electrons

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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• Electronegativity the attractive force that an
  atomic nucleus exerts on electrons
• Electronegativity depends on the number of
  positive charges (protons) and the distance
  between the nucleus and electrons.

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Table 2.3
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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• If two atoms have similar electronegativity, they
  will share electrons equallynonpolar covalent
  bond.
• If one atom has more electronegativity, the
  electrons are drawn to that nucleus. Electrons
  not shared equallypolar covalent bond.

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How does Magnesium (Mg) and Oxygen (O) bind
together?
Magnesium Oxide (MgO)
Ionic Bonds Ionic Compound (SALTS)
Mg Cation Oxygen Anion
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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• Ions electrically charged particles when atoms
  loose or gain electrons
• Cationspositive
• Anionsnegative
• Ionic bonds are formed by the electrical
  attraction of positive and negative ions.
• Saltsionically bonded compounds

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Question 13

• 13. Explain what holds together the atoms in a
  crystal of magnesium chloride (MgCl2)?

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2.3 The formation and function of molecules
depend on chemical bonding between the atoms.

• In a solid, ions are close together and the ionic
  bond is strong.
• In water, the ions are far apart and the
  attraction is much weaker.
• Ions interact with polar moleculessalts dissolve
  in water.

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Strong and weak chemical bonds
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Weak Chemical Bonds

• Hydrogen bonds attraction between the d end of
  one molecule and the d hydrogen end of another
  molecule
• Hydrogen bonds form between H and O and/or H and
  N.
• Important with
• water
• DNA
• Proteins

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Van der Waals Interactions

• Van der Waals interactions
• Occur when transiently positive and negative
  regions of molecules attract each other

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Structure and Function run from large scale body
systems through molecules and atoms.Structure
and function are what Enzymes are all about
Figure 2.17
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Question 14

• 14. In your words, explain why medics pump
  wounded soldiers with morphine on the battlefield?

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Concept 2.4 Chemical reactions make and break
chemical bonds

• Chemical reactions
• Convert reactants to products

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Life is the result of Chemical Reactions

• Photosynthesis
• Is an example of a chemical reaction

Figure 2.18
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Chemical Equilibrium

• Chemical equilibrium
• Is reached when the forward and reverse reaction
  rates are equal

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Questions 15 - 16

• Refer to the reaction between hydrogen and oxygen
  to form water, shown as a ball and stick model on
  page 44. Draw the electron-shell diagram
  representing this reaction.
• Which occurs faster at equilibrium, the formation
  of products from reactants, or reactants from
  products?