The CHEMICAL CONTEXT OF LIFE Atoms and Molecules

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The CHEMICAL CONTEXT OF LIFE Atoms and Molecules
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OBJECTIVES

• Be Familiar With
• Chemical vocabulary discussed in class
• Basic parts of an atom and its properties
• Electrons, their positions energy levels
• Chemical bonds between atoms
• Chemical bonds between molecules

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IMPORTANT VOCABULARY

• Matter
• - Anything that takes up space and has mass
• Element
• - Substance cannot be broken down into other
  substances by chemical reactions

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IMPORTANT VOCABULARY

• Atom
• Smallest chemical unit
• Consists of three subatomic particles

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IMPORTANT VOCABULARY

• Periodic Table
• Organizes elements
• H, C, N and O make up 95 of life
• S, P, Ca, K, Na, Cl, Mg
• Trace elements Fe, I

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IMPORTANT VOCABULARY

• Molecule
• Substance composed of two or more atoms
• Compound
• Substance made of two or more elements

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IMPORTANT VOCABULARY

• Atomic Number
• Subscript
• Equivalent to the number of protons
• If atom is electrically neutral, also equal to
  the number of electrons

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IMPORTANT VOCABULARY

• Atomic Mass
• Superscript
• Sum of protons, neutrons, and electrons
• Protons and neutrons are equal to 1.67 x 10-24
  grams (1 amu).
• Electrons are equal to 9.1 x 10-28 grams (0 amu).

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IMPORTANT VOCABULARY

• Isotope
• Atoms of the same element with differing number
  of neutrons
• Number of protons do not change

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IMPORTANT VOCABULARY

• Ion
• A positive or negatively charged atom or molecule
  by the loss or gain of electron(s)
• Cation- positively charged
• Anion- negatively charged

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Chemical Behavior

• Electrons and Energy levels
• Electrons are only particles involved
• in chemical reactions
• Electrons vary in their energy level
• Energy the ability to do work

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POTENTIAL ENERGY OF ELECTRONS
Nucleus
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1. An electron in an outer shell has a defined
amount of potential energy, Ep-
Ek
2. As the electron falls to a lower energy
shell, its potential energy is converted to
kinetic energy, Ek-
3. Once the electron arrives at a lower electron
shell, the kinetic energy is converted to light
or heat.
Energy is neither created nor destroyed it
simply changes form.
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1. A water molecule sitting at top of a
waterfall has potential energy, Ep.
2. As the molecule falls, the stored energy is
converted to kinetic energy (the energy of
motion), Ek.
Ek
3. When the molecule strikes the rocks below,
its energy Ek is converted to thermal,
mechanical, and sound energy.
Energy is neither created nor destroyed it
simply changes form.
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ELECTRON SHELL MODEL (BOHR MODEL)

• Electrons reside in shells around the atomic
  nucleus
• First shell holds 2 electrons
• Second shell holds 8 electrons
• Third shell holds 8 electrons
• Electrons fill shell(s) closest to nucleus first

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Distribution of electrons in shells of these
elements
Hydrogen
Helium
Neon
Lithium
Beryllium
Oxygen
Boron
Carbon
Nitrogen
Fluorine
Sodium
Phosphorus
Argon
Chlorine
Magnesium
Sulfur
Aluminum
Silicon
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ELECTRON ORBITALS

• Atoms are mostly space!
• Within each shell, electrons reside in orbitals
• Orbitals are a 3D space where it is most
  probable to find electrons
• Orbitals have characteristic shapes

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ATOMS COMBINE BY CHEMICAL BONDS TO FORM MOLECULES

• Chemical Bonds
• Attractions between atoms as a result of electron
  interactions
• Involve valence electrons only
• Help atoms reach noble gas configuration

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ELECTRONEGATIVITY

• Electronegativity
• Affinity of an atom for electrons
• Determines bonds type that forms between atoms!

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Distribution of electrons in shells of these
elements
Hydrogen
Helium
Neon
Lithium
Beryllium
Oxygen
Boron
Carbon
Nitrogen
Fluorine
Sodium
Phosphorus
Argon
Chlorine
Magnesium
Sulfur
Aluminum
Silicon
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BONDS BETWEEN ATOMS

• Covalent Bonds
• Result from the sharing of valence electrons
• Two types
• Nonpolar covalent bonds
• Polar covalent bonds

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BONDS BETWEEN ATOMS

• Non Polar Covalent Bonds
• Occur between two atoms with relatively equal
  affinities for electrons
• Result in equal sharing of electrons

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Non Polar Covalent Bond
H
H
H
H

H2 molecule has two shared electrons
Hydrogen atoms each have one unpaired electron
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Organic Chemistry
Carbons linked in a linear molecule
H
H
C
H
H
C
H
H
C
H
H
C
H
C8H18 Octane
H
C
H
H
C
H
H
C
H
H
C
H
H
Carbons linked in a ring
CH2OH
C
H
O
C6H12O6 Glucose
H
H
C
C
OH
H
C
HO
OH
C
OH
H
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BONDS BETWEEN ATOMS

• Polar Covalent Bonds
• Occur between atoms that differ moderately in
  their affinities for an electron
• Unequal sharing of electron(s) result

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BONDS BETWEEN ATOMS

• Polar Covalent Bonds (Continued)
• Overall charge on molecule is zero
• More electronegative atom has partial (-) charge
• Less electronegative atom has partial () charge

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Polar Non Polar Covalent Bonding
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POLAR NONPOLAR SUBSTANCES

• Polar and nonpolar molecules are not generally
  miscible (dont readily mix)

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BONDS BETWEEN ATOMS

• Ionic bonds
• Transfer of electrons between atoms
• Results when there is a large difference in
  electronegativity between atoms

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BONDS BETWEEN ATOMS

• Ionic bonds
• Na has 1 valence electron (v.e.)
• It must rid itself of this v.e. to become stable
• Na is considered non-electronegative
• Cl has 7 valence electrons
• To achieve stable configuration, it must accept
  one e-
• Cl is considered highly electronegative

Na
Cl
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A sodium ion being formed
Loss of electron
Na
Na
Cation formation
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A chloride ion being formed
Gain of electron
Cl-
Cl
Anion formation
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Table salt is a crystal composed of two ions.
A chloride ion being formed
Gain ofelectron
Cl-
Cl-
Cl
Cl
Cl
Na
Anionformation
Ionic solids dissolve readily in water.
d
d-
d-
Na
d
Cl-
Cl
d
d-
A sodium ion being formed
d
Loss ofelectron
Na
Na
Cation formation
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Bond Type Depends on Electronegativity
Compare the different locations of shared
electrons
Equal sharing of electrons
Transfer of electrons
Y
X-
dY
Xd-
X
X
Ionic bonds (atoms have full charges)
Polar covalent bonds (atomshave partial charges)
Nonpolar covalent bonds (atoms have no charge)
Examples
NaCl
H2O
H2
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ATTRACTIONS WITHIN BETWEEN MOLECULES

• Hydrogen Bonds
• Weak attraction of H atom to an electronegative
  atom on another molecule
• Do not involve physical bonding
• Represented with dotted lines

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BONDS WITHIN BETWEEN MOLECULES

• Hydrogen Bonds
• Water
• Polarity of bonds between H and O allow
• H-bonds to form between adjacent water
  molecules

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BONDS BETWEEN MOLECULES

• Hydrogen Bonds (Continued)
• Hydrogen bonds can also form between a water
  molecule and another (polar) molecule

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HYDROGEN BONDS WITHIN A SINGLE MOLECULE
one large molecule
another large molecule
a large molecule twisted back on itself
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WATER IONIC SUBSTANCES

• Ionic solids dissolve in water
• Due to polar bonds within water molecules

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Ionic solids dissolve readily in water.
d
d-
d-
d
Cl-
Na
d
d-
d
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