The Chemical Context of Life

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Chapter 2

• The Chemical Context of Life
• and Properties of Water

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Why are we studying chemistry?

• Chemistry is the foundation of Biology

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Basics You Should Know

• Matter
• Elements
• Compounds
• Atoms
• Subatomic Particles
• Atomic Number
• Atomic Mass
• Isotopes
• Electron Shells/Energy Levels
• Electron Orbitals

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• Everything is made of matter
• Matter is made of atoms

Hydrogen 1 proton 1 electron
Oxygen 8 protons 8 neutrons 8 electrons
Proton
Neutron
Electron

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The World of Elements
H
C
O
N
P
S
Na
Mg
K
Ca
Different kinds of atoms elements
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Life requires 25 chemical elements

• About 25 elements are essential for life
• Four elements make up 96 of living matter
• carbon (C) hydrogen (H)
• oxygen (O) nitrogen (N)
• Four elements make up most of remaining 4
• phosphorus (P) calcium (Ca)
• sulfur (S) potassium (K)

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Deficiencies

• If there is a deficiency of an essential element,
  disease results

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Trace Elements

• Trace elements Are required by an organism in
  only minute quantities
• Minerals such as Fe and Zn are trace elements

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Bonding properties

• Effect of electrons
• electrons determine chemical behavior of atom
• depends on numberof electrons in atoms
  outermost shell
• valence shell

How does this atom behave?
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Whats themagic number?
Bonding properties
How does this atom behave?
How does this atom behave?
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Elements their valence shells
Elements in the same row have the same number of
shells
Moving from left to right, each element has a
sequential addition of electrons ( protons)
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Elements their valence shells
Elements in the same column have the same valence
similar chemical properties
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Chemical reactivity

• Atoms tend to
• complete a partially filled valence shell
• or
• empty a partially filled valence shell

This tendency drives chemical reactions
and creates bonds
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Ionic bonding

• High electronegativity difference strips valence
  electrons away from another atom
• Electron transfer creates ions (charged atoms)
• Cation (positive ion) anion (negative ion)
• Ex Salts (sodium chloride)

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Covalent Bonding

• Sharing pair of valence electrons
• Number of electrons required to complete an
  atoms valence shell determines how many bonds
  will form
• Ex Hydrogen oxygen bonding in water methane

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Nonpolar covalent bond

• Pair of electrons shared equally by 2 atoms
• example hydrocarbons CxHx
• methane (CH4 )

balanced, stable,good building block
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Polar covalent bonds

• Pair of electrons shared unequally by 2 atoms
• example water H2O
• oxygen has higher electronegativity
• oxygen has stronger attraction for the
  electrons than hydrogen
• water is a polar molecule
• vs poles
• leads to many interesting properties of water

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Hydrogen bonds

• Hydrogen atom covalently bonded to one
  electronegative atom is also attracted to another
  electronegative atom (oxygen or nitrogen)

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Properties of Water
Capillary Action
Good Solvent
Adhesion
Cohesion
Supports Life
High Specific Heat
On Earth, it exists in three phyiscal states
Solid
Gas
Surface Tension
liquid
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Properties of Water

• Earth is ¾ Water
• Supports All of Life
• Most animals and plants contain more than 60
  water by volume.
• All living organisms require water more than any
  other substance

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Properties of Water

• Cohesion/Adhesion
• Surface tension
• Temperature Moderation
• High specific heat
• Evaporative cooling
• Universal solvent

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Effects of Changes in pH

• Water can dissociate Into hydronium ions (H or
  H3O) and hydroxide (OH-) ions
• Changes in the concentration of these ions Can
  have a great affect on pH in living organisms

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Acids and Bases

• An acid
• Is any substance that increases the hydrogen ion
  concentration of a solution
• A base
• Is any substance that reduces the hydrogen ion
  concentration of a solution (more OH- ions)

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Buffers

• The internal pH of most living cells
• Must remain close to pH 7
• Buffers
• Are substances that minimize changes in the
  concentrations of hydrogen and hydroxide ions in
  a solution