Transcript Document 7156339

CHEMISTRY
Concepts and connections
Ch. 2
Atoms, Elements and molecules
• ALL MATTER IS MADE UP OF ATOMS
• ALL MATTER IS ORGANIZED INTO
ELEMENTS (in the Periodic Table)
• The fundamental building blocks of life are
CHEMICALS
• ELEMENTS: fundamental form of matter that
have mass, occupies space and cannot be
decomposed into other substance(elements are
made up of atoms that are unique for that substance)
Atoms
• ATOM: the smallest unit of an element that
still retains the properties of that element
• Living things are composed of about 25
chemical elements.
MOLECULE:
• MOLECULE: two or more atoms bonded
together in fixed proportions.
Example: a water molecule. 2 hydrogen
atoms bonded with an oxygen atom H2O
• Two molecules : 2H2O
• Cells function and do what they do as
a result of chemical reactions
ELEMENTS FOUND IN ALL LIVING
ORGANISMS:
• Living organisms contain about 25 chemicals but the four found in ALL
are : CHON (carbon, hydrogen, oxygen and nitrogen)
• These four make up over 96% of our bodies
• Elements found in most life: CHONPS
• Others important for life are Mg, Na, K, Cl, Ca, I, Fe
• Elements found in very small amounts are “trace
elements” and function as catalysts and co-enzymes
• Ex: iodine (I)
• Chemical symbols are universal. C= carbon H= hydrogen O= oxygen
• N= nitrogen P=phosphorous S= sulfur Mg= magnesium Na= sodium
K= potassium Ca=calcium Fe= iron
– Carbon, hydrogen, oxygen, and nitrogen
•
Table 2.1
Make up the bulk of living matter
CONNECTION
• Trace elements are common additives to food
and water
– Dietary deficiencies in trace elements
•
Can cause various physiological conditions
Figure 2.2A
ATOMS
• Atoms are made up of:
PROTONS (p+) (positive charge) in the
nucleus
NEUTRONS (n) (no charge) in the nucleus
ELECTRONS (e-) (negative charge) in the
energy levels around the nucleus
LE 2-8
Hydrogen
1H
2
Atomic number
He
Atomic mass
First
shell
4.00
Helium
2He
Element symbol
Electron-shell
diagram
Lithium
3Li
Beryllium
4Be
Boron
5B
Carbon
6C
Nitrogen
7N
Oxygen
8O
Fluorine
9F
Neon
10Ne
Sodium
11Na
Magnesium
12Mg
Aluminum
12Al
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Second
shell
Third
shell
Electron Configuration and
Chemical Properties
• The chemical behavior of an atom is
determined by the distribution of electrons
in electron shells
• The periodic table of the elements shows
the electron distribution for each element
Atoms are electrically neutral
• The number of protons(+) in the nucleus =
the number of electrons(-) around it
# of protons= # of electrons
• Atomic number = the number of protons
in the nucleus
• Atomic mass = the number of protons +
the number of neutrons added together
Subatomic Particles
• Atoms are composed of subatomic particles
• Relevant subatomic particles include:
– Neutrons (no electrical charge)
– Protons (positive charge)
– Electrons (negative charge)
• Neutrons and protons form the atomic
nucleus
• Electrons form a cloud around the nucleus
LE 2-4
Cloud of negative
charge (2 electrons)
Electrons
Nucleus
• Valence electrons are those in the
outermost shell, or valence shell
• The chemical behavior of an atom is
mostly determined by the valence
electrons
LE 2-7b
Third energy level (shell)
Second energy level (shell)
Energy
absorbed
First energy level (shell)
Energy
lost
Atomic
nucleus
ISOTOPES
• Isotopes are atoms of a given element that
have the same number of protons and
electrons but have a different number of
neutrons.
• They have the same atomic number but
different mass number.
Ex: Carbon (C) there are 6 protons and 6
electrons in carbon but it can have different # of
neutrons such as 12C, 13C, 14C
•Medical Diagnosis
– Radioactive tracers are often used for diagnosis
•
Figure 2.5A
In combination with sophisticated imaging
instruments
Figure 2.5B
LE 2-6
Cancerous
throat
tissue
Uses of Isotopes
• In medicine and research as labels and
tracers.
For Diagnosis: can take pictures with PET scans and other
devices. we can detect them with scintillating machines
and follow their movements
For treatment: we use radium and cobalt to destroy
cancerous tumors
• To date ancient objects:
Since we know the half life of an element ( time it takes for
half of it to decay to a stable form) we can calculate how
long it has been around.
• Electron arrangement determines the
chemical properties of an atom
– Electrons in an atom
•
Are arranged in shells, which may contain
different numbers of electrons
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Electron
Hydrogen (H)
Atomic number = 1
Figure 2.6
Carbon (C)
Atomic number = 6
Nitrogen (N)
Atomic number = 7
Oxygen (O)
Atomic number = 8
– Atoms whose shells are not full
•
Tend to interact with other atoms and gain,
lose, or share electrons
– These interactions
•
Form chemical bonds
Chemical bonds in living organisms
• The three major chemical bonds used by
elements to build compounds are:
• Ionic bonds
• Covalent bonds
• Hydrogen bonds
IONS
• Atoms become IONS or ionized when
they lose or gain electrons so the number
of protons is different than the number of
electrons.
• When an atom gains electrons it has more
–(negative ) charges. It becomes a
negative ion
• When it loses electrons now it has more
positive charges. It becomes a positive ion
•Ionic bonds are attractions between ions of
opposite charge
– When atoms gain or lose electrons
•
–
Charged atoms called ions are created
–
+
Transfer of
electron
–
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
Figure 2.7A
– An electrical attraction between ions with
opposite charges
•
Results in an ionic bond
– Sodium and chloride ions
•
Bond to form sodium chloride, common table salt
Na+
Cl–
Figure 2.7B
•Covalent bonds join atoms into molecules
through electron sharing
– In covalent bonds
•
Two atoms share one or more pairs of outer shell
electrons, forming molecules
• A molecule consists of two or more atoms
held together by covalent bonds
• A single covalent bond, or single bond, is
the sharing of one pair of valence electrons
• A double covalent bond, or double bond, is
the sharing of two pairs of valence electrons
• Covalent bonds can form between atoms of
the same element or atoms of different
elements
Animation: Covalent Bonds
LE 2-11b
Name
(molecular
formula)
Oxygen (O2)
Electronshell
diagram
Structural
formula
Spacefilling
model
– Molecules can be represented in many ways
Table 2.8
• Unequal electron sharing creates polar
molecules
– A molecule is nonpolar
•
When its covalently bonded atoms share
electrons equally
– In a polar covalent bond
•
Electrons are shared unequally between atoms,
creating a polar molecule
(–)
(–)
O
H
(+)
Figure 2.9
H
(+)
•Hydrogen bonds are weak bonds important
in the chemistry of life
– The charged regions on water molecules
•
Are attracted to the oppositely charged
regions on nearby molecules
– This attraction forms weak bonds
•
Called hydrogen bonds
(–)
Hydrogen bond
(+)
H
(+)
O
(–)
H
(–)
(+)
(–)
(+)
Figure 2.10
WATER
Life began in water and land organisms
essentially carry their wet environment inside
themselves. Water accounts for 75 to 85% of
a cell’s weight, and most cells are surrounded
by it.
About 71% of Earth’s surface is covered by
oceans and human bodies are about 66%
water.
If you weigh 128bl, 85 pounds of you is water.
• Water plays a major role in many of life’s
processes.
WATER’S LIFE-SUPPORTING
PROPERTIES
• Hydrogen bonds make liquid water
cohesive (molecules “stick” to each other)
– Due to hydrogen bonding
– Cohesiveness makes water molecules move
from a plant’s roots to its leaves
– Insects can walk on water due to surface
tension
•
Figure 2.11
Created by cohesive water molecules
• Water’s hydrogen bonds moderate
temperature
– Water’s ability to store heat
•
Moderates body temperature and climate
• Ice is less dense than liquid water
– Hydrogen bonds hold molecules in ice
•
Farther apart than in liquid water
Figure 2.13
Ice
Hydrogen bonds are stable
Hydrogen bond
Liquid water
Hydrogen bonds
constantly break and re-form
– Ice is therefore less dense than liquid water
•
Which causes it to float
– Floating ice
•
•
Prevents lakes and oceans from freezing
solid. The water under the ice remains
warmer
protects the living things beneath the ice
• Water is the solvent of life
– Polar or charged solutes dissolve when water
molecules surround them, forming aqueous
solutions
Na+
–
+
Na+
Cl–
–
+
Cl–
+
–
–
+
+
–
+
–
+
–
–
–
Ion in
solution
Figure 2.14
Salt
crystal
–
WATER PROPERTIES
• Water is the best solvent for living things. It can dissolve more
substances in greater mounts than any other liquid. Everything
that goes In and out of cells is dissolved in H2O
This is because of its polarity and hydrogen bonds.
• Water is a polar molecule (slightly negative at the oxygen end
and slightly positive at the hydrogen end). Polar molecules are
hydrophilic (water loving)
A hydrophobic substance is one that dislikes water, it is
nonpolar .Ex: oils
• Because water forms hydrogen bonds with other water
molecules ,they are spaced apart when frozen, so ice is less
dense than liquid water and it floats on it.
• Ice on the surface insulates the water beneath it, keeping it
warmer.
Water Properties (continued….)
•
•
•
Water has temperature stabilizing effect.
This is because it can absorb a lot of heat
before its temperature changes.
Heat increases the molecular motion so
much that hydrogen bonds are broken and
water molecules escape into the air. This is
evaporation, cooling the surface.
Water’s cohesion creates surface tension.
Cohesion is the capacity to resist
rupturing. Water “sticks together” as a
result of its hydrogen bonds.
Cohesion is very important for plants to
pull water from the soil.
• The chemistry of life is sensitive to acidic
and basic conditions
– A compound that releases H+ ions in solution is
an acid
•
And one that accepts H+ ions in solution is a
base
– Acidity is measured on the pH scale
•
•
From 0 (most acidic) to 14 (most basic)
Neutral pH is 7
Acids, Bases and Buffers: The pH scale
PH is the measure of the H+ (hydrogen ions)
concentration in a solution. The greater the
H+ conc. The lower the pH.
• The scale goes from 0( acidic) to 7 (neutral)
to 14 (basic)
• What is an acid?
A substance that releases hydrogen ions in
solution is an acid. Ex: HCl (hydrochloric
acid)
• What is a base?
Substances that release OH-(hydroxyl ions) in
solution are called bases and are alkaline.
The pH scale
H+
H+ OH– H+
OH– H+ H+
H+ H+
Acidic solution
OH–
OH–
OH–
H+ H+
–
OH– OH
H+ H+ H+
Neutral solution
OH–
OH–
–
OH H+ OH–
OH– OH– –
OH
H+
NEUTRAL
[H+]=[OH–]
1
2
Lemon juice, gastric juice
3
Grapefruit juice, soft drink
4
Tomato juice
5
6
Human urine
7
Pure water
Human blood
8
Increasingly BASIC
(Lower concentration of H+)
H+
Increasingly ACIDIC
(Higher concentration of H+)
pH scale
0
Seawater
9
10
Milk of magnesia
11
Household ammonia
12
Household bleach
13
Oven cleaner
Basic solution
Figure 2.15
14
– The pH of most cells
•
Is kept close to 7 (neutral) by buffers
– Buffers are substances that resist pH change
What are buffers?
• Buffers are substances that the body
uses to prevent big shifts in pH.
• Either will release H+ ions or combine
with H+ ions to keep the balance.
Bicarbonate is an example of one of the
body’s important buffers
CONNECTION
• Acid precipitation threatens the environment
– Some ecosystems are threatened by acid
precipitation
– Acid precipitation is formed when air pollutants
from burning fossil fuels
•
Combine with water vapor in the air to form
sulfuric and nitric acids
– These acids
•
Can kill trees and damage buildings
CHEMICAL REACTIONS
•Chemical reactions change the composition of
matter
– In a chemical reaction
•
Figure 2.17A
Reactants interact, atoms rearrange, and
products result
2 H2
O2
2 H2O
TYPES OF CHEMICAL REACTIONS
Chemical reactions happen every moment
of everyday in every cell of every living
organism.
• During chemical reactions either small
molecules come together to form larger
ones or large molecules break up.
• Whenever chemical reactions take place
bonds form or bonds break and ENERGY
is involved. The energy of the system
changes .
FUNCTIONAL GROUPS
• These “functional groups” are attached
(covalently bonded) to a carbon “backbone”
or chains of carbons to form different
biological molecules.
C-C-C-C-C-C-C-C-C-C-OH hydroxyl group, forms sugars
aldehyde group, forms sugars
-COOH carboxyl group, found in sugars,
fats and amino acids
-NH2
amino group, forms amino acids and
proteins
OXIDATION /REDUCTION REACTIONS
(OIL RIG)
• Oxygen is everywhere in our atmosphere and it
is very reactive.
• Oxidation:
Chemical reaction in which an atom loses
electrons while combining.
Ex: burning anything (combustion) and oxidation (rusting)
• The atom that loses the electrons is oxidized
• Reduction:
The gaining of electrons by another atom.
The one accepting or receiving electrons is
reduced.
CONDENSATION REACTIONS and
HYDROLYSIS REACTION
• Condensation or dehydration reactions: Water
is taken out.
Cells put together large molecules this way.
Enzymes remove an –OH (hydroxyl) from one
molecule and a H from another, then a covalent
bond is formed and water is formed. Ex: building
proteins.
• Hydrolysis : Water is added.
Breaking down the covalent bonds and splitting a
molecule into 2 or more parts. A H and –OH from a
water molecule are attached to the exposed ends.
Hydrolysis (breaking bonds) releases energy. Ex:
digestion.
Endergonic and Exergonic
reactions
• Exergonic: a chemical reaction that
releases energy (energy out)
Ex: Cellular respiration, light display of a
firefly,
Endergonic reaction: Chemical reaction that
requires an input of energy. (energy in).
Ex: photosynthesis, building new molecules.
EXOTHERMIC and ENDOTHERMIC
Reactions
• Reactions that give off heat energy are
EXOTHERMIC
Ex: gas moving car, body using glucose
• Reactions that use or take in heat energy
are ENDOTHERMIC
Ex; cooking
Questions
• 1. What caused the Brown Pelican to become an
endangered species? Is it still one?
• 2. We divide the study of life into levels of biological
organization. What are those levels starting with the
smallest?
• 3. Organisms that provide food for an ecosystem are
called______.
• 4. Those that recycle dead matter into simple chemicals
are ______.
• 5. Chemical nutrient are _____ though an ecosystem, but
energy_____.
• 6.What is the unit of structure and function of all life?