Transcript H +

Warm-up Question
Draw an atom and label these parts: electron,
proton, neutron, nucleus and orbital.
Chapter 2: pp. 20-36
Basic Chemistry
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Na
Cl
sodium atom (Na)
chlorine atom (Cl)
–
+
Cl
Na
sodium ion (Na+)
Na+ Cl–
chloride ion (Cl–)
sodium chloride (NaCl)
a.
b.
(Crystals): © Charles M. Falco/Photo Researchers, Inc.; (Salt shaker): © Erica S. Leeds
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2.1 Chemical Elements
Matter:
Anything that has mass and occupies space
Matter exists in three states: solid, liquid, and gas
3
A. Elements
Can't be broken down into simpler substances with
diff properties by ordinary means
6 are basic to life: CHNOPS
95% of the whole organism
B. Atoms


Smallest unit of an element
Atoms composed of subatomic particles:




Protons - positive charge; found in the
nucleus
Neutrons - no charge;found in the nucleus
Electrons - negative charge; found in
electron shell
Atoms contain specific numbers of protons,
neutrons, and electrons.
5
C. Atomic # and Mass #
Atomic
Number
Mass
Number
6
12
6
Carbon
C
Atomic
Symbo
l
Atomic # = number of
protons of the
element
Atomic mass of an
atom depends on the
presence of
subatomic particles
Atomic number =
proton number;
Atomic mass or mass
number = protons and
neutrons
6
D. Isotopes
Isotopes:
Atoms of the same element with a differing
numbers of neutrons (and therefore have different
atomic masses).
12
6
13
6
C
Carbon 12
•
14
6
C
Carbon 13
C
Carbon 14
Some isotopes spontaneously decay
 Radioactive
 Give
 Can
off energy in the form of rays and subatomic particles
be used as tracers
 Mutagenic
– Can cause cancer
7
Some Medical Uses for Low Level Radiation

MRI, CT, Nuclear Medicine
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larynx
thyroid gland
trachea
a.
b.
a: © Biomed Commun./Custom Medical Stock Photo; b(Right): © Hank Morgan/Rainbow; b(Left): © Mazzlota et al./Photo Researchers, Inc
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Some Medical Uses for High
Level Radiation

Radiation can kill cancer cell

Radiation can preserve food longer
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a.
b.
a: (Peaches): © Tony Freeman/PhotoEdit; b: © Geoff Tompkinson/SPL/Photo Researchers, Inc.
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Electrons and Energy
Atoms normally have as many electrons as
protons
Opposite charges balance leaving atom
neutral
Electrons are attracted to the positive
nucleus
Revolve around nucleus in orbitals
Can be pushed into higher orbitals with energy
Release that energy when they fall back to lower
orbital
Different energy levels referred to as electron
shells
10
Animation
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The Octet Rule for Distribution of Electrons
Bohr models show electron shells as
concentric circles around nucleus
Each shell has two or more electron orbitals
Innermost shell has two orbitals
Others have 8 or multiples thereof
The outermost electron shell determines the
reactivity of the element
If 3 or less – Tendency to donate electrons
If 5 or more – Tendency to receive electrons
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Bohr Models of Atoms
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H
hydrogen
1
H
1
electron
electron shell
nucleus
C
N
carbon
12
C
6
nitrogen
14
N
7
P
S
phosphorus
31P
15
sulfur
32S
16
O
oxygen
16 O
8
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2.2 Compounds and Molecules
Compound - when atoms of two or more
different elements bond together
CO2, H2O, C6H12O6, etc.
Characteristics dramatically different from original
elements
Molecule and compound is used
interchangeably
In Biology molecule is used e.g. molecule of water
(H2O) molecule of glucose (C6H12O6 )
Bonds that exist between atoms in molecules
contain energy
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Types of Bonds: Ionic Bonding

Ionic bond - forms when electrons are
transferred from one atom to another atom.
 Held together by attraction between
negative and positive charge
15
Types of Bonds: Ionic Bond Example
Sodium (Na):
Has only 1 electron in its outermost shell
Chlorine (Cl):
Has 7 electrons in its outermost shell
In a reaction between Na and Cl
Na loses an electron and becomes a positive ion
(Na+)
Cl gains an electron and becomes a negative ion
(Cl-)
Attraction of oppositely charged ions holds the
two atoms together in an ionic bond
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Warm-Up Question
What do atoms that cannot form ionic bonds do to
become stable?
Covalent Bonding
Atoms share a pair or pairs of electrons to fill
outermost shell
•Single covalent bond
•Double covalent bond
•Triple covalent bond
Nonpolar Covalent Bonds
In nonpolar covalent bonds, sharing
of electrons is equal, i.e. the
electrons are not attracted to either
atom to a greater degree
One atom “want” (with a specific intensity) to
donate electron(s)
The other atom “want,” (with the same intensity)
to receive electron(s)
The bond electrons will spend about equal time
with both atoms
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Nonpolar Covalent Bonds
Atoms share
electrons equally
 Nuclei of atoms have
same number of
protons
 Example: Hydrogen
gas (H-H)

molecular hydrogen (H2)
H—H
Polar Covalent Bonds
Number of protons in
nuclei of participating
atoms is not equal
 Electrons spend
more time near
nucleus with most
protons
 Water - Electrons
more attracted to O
nucleus than to H
nuclei

water (H2O)
H—O—H
Animation
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22
2.3 Chemistry of Water
Water (H2O or H–O–H) is a polar molecule
Electrons spend more time with O than H’s
H’s become slightly +, O slightly –
Hydrogen bond – attraction of slightly positive H to a
slightly negative atom (N, O, S)
Weaker than ionic/covalent
Many together = strong
Help to maintain the proper structure and function of
complex molecules such as proteins and DNA.
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Water Molecule
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Electron Model
Ball-and-stick Model
Space-filling Model
Oxygen attracts the shared
electrons and is partially negative.
–
O
O
H
O
H
H
104.5°
H
H
+
H
+
Hydrogens are partially positive.
a. Water (H2O)
+
H
O
–
hydrogen
bond
H
+
b. Hydrogen bonding between water molecules
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High Heat Capacity
The many HB help water absorb heat without
large change in temperature
Holds onto heat and temp falls slowly
protecting organisms from rapid internal
temp changes
25
High Heat of Evaporation
Large numbers of hydrogen bonds must be
broken to evaporate water
To raise water from 100 to 101 ºC; ~540 calories!
This is why sweating (and panting) cools
Evaporative cooling is best when humidity is low
because evaporation occurs rapidly
Evaporative cooling works poorest when humidity
is high because evaporation occurs slowly
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Evaporative Cooling of Animals
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Calories of Heat Energy / g
800
Gas
600
540
calories
400
200
Liquid
80
calories
Solid
0
freezing occurs
0
evaporation occurs
20 40 60 80 100 120
Temperature (°C)
a. Calories lost when 1 g of liquid water freezes and
calories required when 1 g of liquid water evaporates.
b. Bodies of organisms cool when their heat is used
to evaporate water.
© Grant Taylor/Getty Images
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Properties of Water: Heat of Fusion
Heat of fusion (melting)
To raise ice from -2 to -1 ºC; ~1 calorie
To raise water from -1 to 0 ºC; ~1 calorie
To raise water from 0 to 1 ºC; ~80 calories!
This is why ice at 0 ºC keeps stuff cold MUCH
longer than water at 1 ºC
This is why ice is used for cooling
NOT because ice is cold
But because it absorbs so much heat before it will
warm by one degree
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Water as a Solvent
Solutions consist of:
A solvent (the most abundant part) and
A solute (less abundant part) that is dissolved in the
solvent
Polar compounds readily dissolve; hydrophilic
Nonpolar compounds dissolve only slightly;
hydrophobic
Ionic compounds dissociate in water
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Properties of Water: Uniqueness of Ice
Frozen water less dense than liquid water
Freeze from top down which insulates and
prevents water below from freezing
Melting ice draws heat from the environment
30
Water as a Transport Medium
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Water evaporates,
pulling the water
column from the
roots to the leaves.
H2 O
Water molecules
cling together and
adhere to sides of
vessels in stems.
Water enters a
plant at root cells.
H2O
31
Density of Water at Various Temperatures
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ice lattice
1.0
Density (g/cm3)
liquid water
0.9
0
4
Temperature (ºC)
100
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Water Cohesion

Hydrogen bonding holds
molecules in liquid water
together

Creates surface tension (skin
on the water)

Allows water to move as
continuous column upward
through stems of plants
2.4 pH of Water: Acids

When water ionizes or dissociates, it
releases a small but equal number of
hydrogen (H+) ions and hydroxide (OH-)
ions

Acids donate hydrogen ions


Dissociate in water and release hydrogen ions
(H+) e.g. HCl → H+ + Cl
Sour to taste
35
pH of Water: Bases
Bases remove hydrogen ions
Either take up hydrogen ions (H+) or release
hydroxide ions (OH-)
Bitter to taste
36
pH Scale
pH scale used to indicate acidity and
alkalinity of a solution.
37
Buffers and pH
Buffers are solutes in water that resist
change in pH
When H+ is added, buffer may absorb, or counter
by adding OHWhen OH- is added, buffer may absorb, or counter
by adding H+
38
Buffers in Biology
Health of organisms requires maintaining pH
of body fluids within narrow limits
Human blood normally 7.4 (slightly alkaline)
Many foods and metabolic processes add or
subtract H+ or OH- ions
Reducing blood pH to 7.0 results in acidosis
Increasing blood pH to 7.8 results in alkalosis
Both life threatening situations
Bicarbonate ion (-HCO3) in blood buffers pH to 7.4
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