Module 1C – Basic Chemistry
„
Objective # 6
Chemistry – the scientific study of the
structure and properties of matter
List the 3 main types of
subatomic particles and
indicate the mass and
electrical charge of each.
Why do we study chemistry in a biology
course?
¾ All living organisms are composed of
chemicals. To understand life, we must
understand the structure, function, and
properties of these chemicals.
„
1
Objective 6
Name
Proton
2
Objective # 7
Symbol Charge Mass
Mass
(Daltons) Number
p
+1
1.00728
1
Neutron
n
0
1.00867
1
Electron
e
-1
0.00055
0
Describe the basic structure of the
atom and be able to define the
following terms: nucleus, orbital,
energy level, isotope, and ion.
3
Objective 7
Objective 7
„ Each
4
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atom is composed of:
Hydrogen
¾ Protons
and neutrons which are densely
packed together in the central part of the
atom called the nucleus.
¾ Electrons which are in constant motion
around the nucleus.
[Note: most hydrogen atoms have no neutrons
and atoms can lose some or all of their
electrons]
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1 Proton
1 Electron
Oxygen
8 Protons
8 Neutrons
8 Electrons
Proton
Neutron
(Positive charge) (No charge)
Electron
(Negative charge)
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1
Objective 7
Objective 7
„ Orbitals:
As electrons move around the nucleus,
they do not follow a specific path and it is
impossible to say exactly where any specific
electron is at any given time. However, the
volume of space where there is a 90%
chance of finding a particular electron is
called its orbital.
¾
¾
¾
¾
hold a maximum of 2 electrons each.
come in a variety of shapes, which are
represented by probability clouds.
several orbitals may be the same average
distance from the nucleus and thus contain
electrons of the same average energy. Such
electrons are said to occupy the same energy
level or shell.
Energy levels or shells are often represented as
concentric circles around the nucleus
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Objective 7
The first energy level has one spherical
orbital:
8
Objective 7
The second energy level has 1 spherical orbital
(2s) and 3 dumbbell-shaped orbitals (2p):
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required for reproduction or display.
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Objective 7
Objective 7
Here you can see a composite of all 5
orbitals found in the first 2 energy levels:
The higher the energy level, the farther
from the nucleus the electrons tend to
be , and the more energy they have:
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2
Objective 7
Objective 7
Rules for filling energy levels:
¾ The first electrons enter the K shell, up to
a maximum of 2.
¾ The next electrons enter the L shell, up to
a maximum of 8.
„
„ The
pattern for filling higher shells
becomes more complex and will not
concern us. However, what you
should remember is that even though
any shell beyond L can hold more than
8 electrons, it will not hold more than
8 when it is the outermost shell.
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Objective 7
Objective 7
„ Atoms
that have the same
number of protons but different
numbers of neutrons are called
isotopes:
Isotopes of Carbon
Carbon-12
6 protons
6 neutrons
Carbon-13
6 protons
7 neutrons
Carbon-14
6 protons
8 neutrons
6 electrons
6 electrons
6 electrons
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Objective 7
„
Objective 7
Normally, the number of electrons in an atom
equals the number of protons and the overall
charge of the atom is zero.
However, atoms often gain or lose electrons:
¾ If an atom gains electrons, it will have an extra
negative charge for each electron gained.
¾ If an atom loses electrons, it will have an extra
positive charge for each electron lost.
„
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The gain of electron(s) is called reduction
and the loss of electrons is called oxidation.
„ Atoms that have gained or lost electrons
and are no longer electrically neutral are
called ions:
¾ positive ions = cations
¾ negative ions = anions
„
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3
Objective 7
Objective # 8
–
+
Define the term “element” and
know the names and chemical
symbols of the principle
elements found in living
organisms.
+
Oxidized
Reduced
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Objective 8
Objective 8
„ Element:
A copy of the Periodic Table can be seen
on the next slide. Each box in the table
represents one element.
„ Elements found in living organisms in
more than trace amounts are shaded in
green . Of these, 4 elements (carbon,
hydrogen, oxygen, and nitrogen) make up
about 96% of the mass of living organisms.
„
¾A
substance composed of only one
type of atom – i.e. all the atoms have
the same number of protons.
„ All atoms of a given element have the
same number of protons. However,
the number of neutrons and electrons
can vary.
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Objective 8
Objective # 9
„
23
Be able to determine the number of
protons, neutrons, and electrons in an
atom if you know its atomic number,
atomic mass, and overall charge. Also be
able to determine the number of electrons
in each energy level of an atom if you
know the total number of electrons
present.
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4
Objective 9
Objective # 10
# p = atomic number
„ # n = atomic mass – atomic number
„ # e:
¾ If overall charge is 0, #e = #p
¾ If overall charge is +, #e = #p minus one
for each overall + charge
¾ If overall charge is -, #e = #p plus one for
each overall - charge
Define the term “molecule” and
explain how the molecular
formula (or chemical formula)
and the structural formula are
used to provide information
about a molecule.
„
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Objective 10
Objective 10
Molecule: a unit composed of two or more
atoms joined together by chemical bonds:
„ Molecular formula or chemical formula:
tells us what types of atoms and how many
of each are joined together.
„ Structural formula: shows us the actual
arrangement of the atoms.
„
H
O
C
H
O
O
H2CO3
Carbonic acid
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Objective # 11
28
Objective 11
Explain the difference between
an element, a compound, and a
mixture.
29
„
Element: a substance composed of only
one type of atom (all the atoms have the
same number of protons). The atoms may
occur signally, or they may be joined to
form molecules. The smallest unit of an
element that retains the properties of the
element is an atom. e.g. hydrogen
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5
Objective 11
Objective # 12
Compound: a substance composed of 2 or
more elements that have been joined by
chemical bonds. The smallest unit of a
compound that retains the properties of
the compound is a molecule. e.g. water
„ Mixture: a combination of 2 or more
substances that do NOT chemically
combine and retain their individual
properties. e.g. sugar mixed with salt
Explain how the number of
electrons in the outermost shell
of an atom affects the number
and type of chemical bonds the
atom can form.
„
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32
Atoms that lack a stable outer shell of
electrons are reactive:
Objective 12
Electrons in the outermost shell are called:
valence electrons
„ Atoms join together in ways that give each
atom a stable outer shell of electrons:
¾ If the first shell is the outer shell, it is stable
with 2 electrons.
¾ If any other shell is the outer shell, it is
stable with 8 electrons.
„
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Nonreactive
Reactive
2 protons
2 neutrons
2 electrons
7 protons
7 neutrons
7 electrons
K
K
L
2+
7+
Helium
Objective 12
34
Objective 12
How can an atom obtain a stable outer
shell of electrons if it doesn’t already have
one?
¾ Gain electrons
¾ Lose electrons
¾ Share electrons
„
„
Nitrogen
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What determines which one?
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„ Different
atoms attract their outer
electrons with different intensity.
The electronegativity of an atom is
the amount of energy needed to
remove electrons. The more
strongly an atom attracts electrons,
the higher its electronegativity.
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6
Objective 12
Objective 12
„ In
general:
¾ The closer the electrons are to the
nucleus, the higher the
electronegativity.
¾ The more nearly full the shell is,
the higher the electronegativity.
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Objective 13a
Objective # 13
„
Discuss the mechanism involved in
forming the following types of chemical
bonds, describe their characteristics, and
be able to give examples of each:
a) Ionic bond
b) Nonpolar covalent bond
c) Polar covalent bond
d) Hydrogen bond
Ionic bond:
¾ If an atom with a very high electronegativity
comes near an atom with a very low
electronegativity, there may be a transfer of
electrons from the 2nd atom to the 1st to give
both atoms a stable outer shell.
¾ The transfer of electrons produces oppositely
charged ions that attract each other to form
an ionic bond. e.g. Na and Cl
„
39
Objective 13a
40
Objective 13a
Formation of Ionic Bonds – NaCl
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Objective 13b
Non-polar Covalent bond
Objective 13b
Nonpolar covalent bond:
¾ If 2 atoms with the same electronegativity
come near each other, neither can remove
electrons from the other. However, they may
share electrons to obtain a stable outer shell.
¾ Since the atoms have the same
electronegativity the electrons are shared
equally. e.g. two H atoms
„
43
–
+
+
–
H2 (hydrogen gas)
44
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Objective 13c
Objective 13c
Polar covalent bond:
¾ If 2 atoms have different electronegativities,
but the difference is not large enough to
allow one atom to remove electrons from
the other, they may share electrons
unequally.
¾ The electrons tend to stay closer to the
atom with the higher electronegativity.
e.g. H2O:
„
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δ+
+
δ–
Hydrogen
8+
8n
Oxygen
δ+
δ–
+
Hydrogen
Polar Covalent Bond
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Objective 13b
Objective 13b
Atoms that share one pair of electrons are
joined by a single covalent bond
„ Atoms that share 2 pairs of electrons are
joined by a double covalent bond
„ Atoms that share 3 pairs of electrons are
joined by a triple covalent bond
„
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8
Objective 13d
Objective 13d
Hydrogen bond:
¾ The weak attraction between a covalently
bound H atom with a slight positive charge
and another covalently bound atom with a
slight negative charge.
¾ May occur between different molecules or
between different parts of the same
molecule:
Hydrogen
bonds can
form
between 2
different
molecules
„
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Objective 13d
Objective 13
Electrostatic bonds are formed by an
attraction between opposite charges:
¾ Hydrogen bonds
¾ Ionic bonds
„ Covalent bonds are formed by a sharing of
electrons:
¾ Polar covalent – unequal sharing
¾ Nonpolar covalent – equal sharing
„
Hydrogen
bonds can
also form
between
different
parts of the
same
molecule
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Objective 14
Objective # 14
Describe the structure of the water
molecule. List and describe the
properties of water, and explain why
these properties are so important to all
living organisms.
δ+
+
δ–
Hydrogen
8+
8n
Oxygen
δ+
δ–
+
Hydrogen
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Water Molecule
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Objective 14
Objective 14
Cohesion
Water molecules attract
other water molecules
Adhesion
Water molecules attract
other charged substances
Surface tension
Surface water molecules
cling to each other
Capillarity
Water molecules are drawn
up a narrow tube
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Objective 14
Objective 14
A large amount of heat must
be absorbed or lost to change
the temperature of water
A large amount of heat needed
to change water from a liquid
to a gas
A large amount of heat needed
to change water from a solid
to a liquid
High specific
heat
High heat of
vaporization
High heat of
fusion
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Lower density as Below 0oC a regular
crystalline structure forms
a solid
Dissolves ions
and polar
molecules
Repels nonpolar
molecules
Substances attracted to
water are called
hydrophilic
Substances repelled by
water are called
hydrophobic
57
Objective 14
58
Objective 14
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Unstable hydrogen
bonds
Liquid water
Stable
hydrogen
bonds
Ice
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Objective # 15
Objective 15
Describe the process of
dissociation and be able to
distinguish between acids, bases,
and salts.
„
Because of the polar structure of water,
many ionic and polar substances are pulled
apart into oppositely charged ions when
they dissolve in water. This is called
ionization or dissociation.
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Objective 15
„
„
Objective 15
Substances held together by relatively weak
ionic bonds show a large amount of
dissociation in water:
¾ NaCl → Na+ + ClThese substances are called salts. Because
they are good conductors of electricity,
they are also called electrolytes.
„
Substances held together by stronger
covalent bonds may also show some
dissociation when dissolved in water:
¾ CH3COOH
„
→ CH3COO- + H+
In fact, water itself undergoes a small
amount of dissociation:
¾ H2O
→ H+ + OH-
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Objective 15
„ In
that increase the [H+] of a
solution are called acids:
pure water:
¾ [H+]
„ In
Objective 15
„ Substances
= [OH-] = 1 x 10-7 M
¾ HCl
all aqueous solutions:
¾ [H+]
[OH-] = 1 x 10-14 M2
→ H+ + Cl-
that decrease the [H+] of a
solution are called bases:
„ Substances
means as the [H+] increases, [OH-]
decreases, and vice versa.
„ This
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¾ NaOH
→ Na+ + OH66
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Objective # 16
Objective 16
pH is used to measure how acidic or basic
a solution is.
„ pH is defined as the negative log of the
[H+] of a solution.
„ If a solution has a [OH-] of 1x10-3 M,
¾ What is its [H+]?
¾ What is its pH?
„
Describe the pH scale and know
how to use it.
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Objective 16
68
Objective # 17
Explain the role that buffers
play in living organisms.
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Objective 17
70
Objective 17
„A
buffer is a substance that helps
minimize the change in the pH of a
solution when acids or bases are
added.
„ Buffers work by releasing H+ when
their concentration falls and absorbing
H+ when their concentration rises.
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Relationship between pH and
amount of base added
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12
Objective 17
„ Buffers
are important to living
organisms because most cells can
survive and function normally only
within a relatively narrow pH
range.
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