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Chapter 2 Quiz
1. One of the four most common elements in living organisms is?
2. What trace element is commonly added to table salt to prevent goiters?
3. Chemical bonds are formed by the interaction of which subatomic particle?
4. What type of bonds are important in the ability of water to regulate temperature?
5. Is a solution with a pH of 2 more acidic than a solution a pH 7?
Ch. 2 The Chemical Basis of LifeI.Elements and Compounds
A. Most common and trace elements
II. Subatomic particlesA. Radioactive isotopesB. Placement of electrons in shells
aIII. Bonds bind together compounds
through electron interactionsA. Single, double, covalent, ionic,
polar, nonpolar, hydrogenV. Acids and BasesIV. Chemical reactionsA. How to write a chemical reaction
Elements and Compounds
• Everything around us is made of chemicals – these may be in two forms
– An element is a substance that cannot be broken down to other substances by chemical reactions
– A compound is a substance consisting of two or more elements in a fixed ratio
• A compound has characteristics different from those of its elements
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Periodic table of the elementsOrganization of the periodic table
Periodic table of the elementsOrganization of the periodic table
Periodic table of the elements
Most common elements in the human body
Table 2-1
• Neutrons (neutral) and protons (+)form the atomic nucleus
• Electrons (-) form a cloud around the nucleus
Subatomic particles
Atomic Number and Atomic Mass
• Atoms of the various elements differ in number of subatomic particles• An element’s atomic number is the number of protons in its nucleus• An element’s mass number is the sum of protons plus neutrons in the nucleus • Atomic mass, the atom’s total mass, can be approximated by the mass number
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
What element is this?
Is it electronically neutral or charged?
Atomic Number and Atomic Mass
• Atoms of the various elements differ in number of subatomic particles• An element’s atomic number is the number of protons in its nucleus• An element’s mass number is the sum of protons plus neutrons in the nucleus • Atomic mass, the atom’s total mass, can be approximated by the mass number
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
What is the atomic number? Mass number? How many protons, neutrons or electrons does this element have?
What element is this? What is the atomic number? Mass number? How many protons, neutrons or electrons does this element have?
Question
• Points to remember– Protons + neutrons = mass number– Protons = atomic number– Uncharged atoms have the same number of
protons and electrons
• An uncharged atom of carbon has an atomic number of 6 and an atomic mass of 13. How many electrons does carbon have?
Reviewing concepts
Elements differ in their number of protons, neutrons, and electrons
Helium has two protons, two neutrons, and two electrons
Carbon has six protons, six neutrons, and six electrons
Copyright © 2009 Pearson Education, Inc.
Electroncloud
Protons
2e–Nucleus
Electrons
Massnumber = 4Neutrons
2
2
2
Reviewing concepts
2.4 Atoms consist of protons, neutrons, and electrons
Although all atoms of an element have the same atomic number, some differ in mass number
– The variations are isotopes, which have the same numbers of protons and electrons but different numbers of neutrons
– One isotope of carbon has 8 neutrons instead of 6 (written 14C)
– Unlike 12C, 14C is an unstable (radioactive) isotope that gives off energy
– A radioactive isotope is an isotope that decays
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Mass Extinction
Time Line
CretaceousJurassic
Mammals begin to dominateDinosaurs dominate Become extinct
How have scientists formed this timeline?
2.5 Radioactive isotopes can help or harm us
Living cells cannot distinguish between isotopes of the same element
1. Therefore, when radioactive compounds are used in metabolic processes, they act as tracers
2. Radioactivity can be detected by instruments
With instruments, the fate of radioactive tracers can be monitored in living organisms
Copyright © 2009 Pearson Education, Inc.
Fig. 2-7
Cancerous
throat
tissue
2.5 Radioactive isotopes can help or harm us
In addition to benefits, there are also dangers associated with using radioactive substances
– Uncontrolled exposure can cause damage to some molecules in a living cell, especially DNA
– Chemical bonds are broken by the emitted energy, which causes abnormal bonds to form
– Chernobyl-Apart from the 57 direct deaths in the accident itself, UNSCEAR originally predicted up to 4,000 additional cancer cases due to the accident
Copyright © 2009 Pearson Education, Inc.
Radioactivity can be good or bad“Natural” can be good or bad
The dangers posed by certain chemicals in our food and broader environment often lead people to associate chemicals with harm. People might not want chemicals added to their food or in their environment
Chemicals both natural and artificial are made of the same elements
Naturally occurring toxins
Tetanus
Botulinum
As mentioned before with ginko biloba herbal supplements are unregulated by FDA
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2.2 Trace elements are common additives to food and water
Several chemicals are added to food for a variety of reasons
1. Help preserve it
2. Make it more nutritious
3. Make it look better
Check out the “Nutrition Facts” label on foods and drinks you purchase
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A Goiter in a Malaysian woman, a symptom of iodine deficiency.
2.2 Trace elements are common additives to food and water
Ex. Good additive
2.2 Trace elements are common additives to food and water
More additives
Ex. Iron
Video1
Video2
Quiz 1 1. What type of cell contains a nucleus, prokaryotic or eukaryotic?
2. Of the following options, list which ones are consistent with Darwin’s theory of evolution.
a. Natural selection can lead to the appearance of new species.
b. Natural selection ensures that the organism that is most adapted to its environment will live to pass on its genes.
c. Individual organisms exhibit genetic change during their life spans to better fit their environment.
d. Natural selection is based in part on the overproduction of offspring.
e. Individuals in a population exhibit variations, some of which are heritable.
3. T/F A controlled experiment will have at least two groups. One is called the experimental group which will be compared to the control group.
4. Of the three domains discussed, name one domain that contains prokaryotes.
5. T/F A fungus kills 99% of a daisy population. You would expect the next generation of daisies to be more resistant to the fungus.
6. Name one of the four most common elements in living organisms.
7. Which of the following is not found in the nucleus of an atom. Proton, neutron, electron.
T/F
3. One of the four most common elements in living organisms is?
4. What trace element is commonly added to table salt to prevent goiters?
5. Chemical bonds are formed by the interaction of which subatomic particle?
6. What type of bonds are important in the ability of water to regulate temperature?
7. Is a solution with a pH of 2 more acidic than a solution a pH 7?
2.6 Electron arrangement determines the chemical properties of an atom
Only electrons are involved in chemical activity
Electrons occur in energy levels called electron shells
– Information about the distribution of electrons is found in the periodic table of the elements
Copyright © 2009 Pearson Education, Inc.
Magnesium
Lithium
Hydrogen
Thirdshell
Firstshell
Secondshell
Sodium
Beryllium
Aluminum
Boron
Silicon
Carbon
Phosphorus
Nitrogen
Sulfur
Oxygen
Chlorine
Fluorine
Argon
Neon
Helium
2.6 Electron arrangement determines the chemical properties of an atom
An atom may have one, two, or three electron shells
– The number of electrons in the outermost shell determines the chemical properties of the atom
– The first shell is full with two electrons, whereas the second and third will hold up to eight electrons
Copyright © 2009 Pearson Education, Inc.
2.6 Electron arrangement determines the chemical properties of an atom
Atoms want to fill their outer electron shells
1. To accomplish this, the atom can share, donate, or receive electrons
2. This results in attractions between atoms called chemical bonds
Copyright © 2009 Pearson Education, Inc.
Magnesium
Lithium
Hydrogen
Thirdshell
Firstshell
Secondshell
Sodium
Beryllium
Aluminum
Boron
Silicon
Carbon
Phosphorus
Nitrogen
Sulfur
Oxygen
Chlorine
Fluorine
Argon
Neon
Helium
All elements have an innate desire to have a filled valence shell
How many electrons does the first shell hold? Second? Third?
Because elements want to have a completely filled valence shell they will react with other elements to accomplish this
Some elements have electrons to donate or share others are on the receiving end of things
In the end the elements will come together to form a compound
Compounds are always formed through the interactions of electrons between two different elements
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Types of chemical bonds to know It is imperative that you completely understand 2.6-2.10- hint, hint
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Sharing of electrons
Water is another example of covalent bonds
Question
A hydrogen atom contains one electron. How many covalent bonds can it form?
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Atoms strip electrons from their bonding partners, resulting in both
atoms having a charge (ions)
NO SHARING as in covalent bonds
Atoms strip electrons from their bonding partners, resulting in both
atoms having a charge (ions)
NO SHARING as in covalent bonds
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single – represented by one line (H-H), one pair of electrons is shared
Double – represented by two lines (O=O), two pairs of electrons are shared
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Single bond
Double bond
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
• Electronegativity is an atom’s attraction for the electrons in a covalent bond
• The more electronegative an atom, the more strongly it pulls shared electrons toward itself
• Electronegativity is the cause of polar bonds
• Oxygen is very electronegative
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Electronegativity
• In a nonpolar covalent bond, the atoms share the electron equally
• In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electron equally
• Unequal sharing of electrons causes a partial positive or negative charge for each atom or molecule – giving the compound two opposite “poles”
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Important Example
(–)
(+)(+)
H H
O
H2O
Oxygen is greedy for electrons and doesn’t share well. Oxygen is more electronegative than hydrogen. It pulls the electrons of the covalent bond.
2.9 Unequal electron sharing creates polar molecules
In molecules of only one element, the pull toward each atom is equal, because each atom has the same electronegativity
1. The bonds formed are called nonpolar covalent bonds
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2.9 Unequal electron sharing creates polar molecules
Water has atoms with different electronegativities
– Oxygen attracts the shared electrons more strongly than hydrogen
– So, the shared electrons spend more time near oxygen
– The result is a polar covalent bond
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2.9 Unequal electron sharing creates polar molecules
In H2O the oxygen atom has a slight negative charge and the hydrogens have a slight positive charge
1. Molecules with this unequal distribution of charges are called polar molecules
Copyright © 2009 Pearson Education, Inc.
(–) (–)
O
HH
(+) (+)
Types of chemical bonds to know
Bonds are interactions of electrons between atoms that result in them staying close together
Covalent
Ionic
Single
Double
Polar
Nonpolar
Hydrogen – ex. results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on ammonia, hydrogen bonds are weak interactions
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
2.10 Hydrogen bonds are weak bonds important in the chemistry of life
Some chemical bonds are weaker than covalent bonds
Hydrogen, as part of a polar covalent bond, will share attractions with other electronegative atoms
1. Examples are oxygen and nitrogen
Water molecules are electrically attracted to oppositely charged regions on neighboring molecules
– Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond
Copyright © 2009 Pearson Education, Inc.
Animation: Water Structure
Hydrogen bond
Hydrogen bondWater molecules stick to other water molecules because hydrogen bonds form between the hydrogen atoms of one water molecule and the oxygen atoms of other water molecules.
Water’s life supporting properties
• Four fabulous properties of water that facilitate life as we know it:
– Cohesive behavior – surface tension
– Ability to moderate temperature
– Expansion upon freezing
– Versatility as a solvent
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2.15 The chemistry of life is sensitive to acidic and basic conditions
A few water molecules can break apart into ions
– Some are hydrogen ions (H+)
– Some are hydroxide ions (OH–)
– Both are extremely reactive
– A balance between the two is critical for chemical processes to occur in a living organism
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pH
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed
• H2O H+ + OH-
• In neutral water, they are present in equal concentrations.
Hydrogen ion Hydroxide ion
Acids and Bases
• An acid is any substance that increases the H+ concentration of a solution
– HCl H+ + Cl-
• A base is any substance that reduces the H+ concentration of a solution
– NaOH Na + + OH- *
* The hydroxide ion will react with the H+ ions in the solution to create water, in this reaction it will indirectly reduce the H+ concentration of a solution
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
See-saw of ions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
H+
OH-
H+
OH-
H+ OH-
Acid: low pH
Neutral
Base: high pH
Acid Base
pH Less than 7 Greater than 7
[H+] increases decreases
How are all of these bonds formed and then broken? Chemical reactions are the making and breaking of chemical
bonds
The starting molecules of a chemical reaction are called reactants
The final molecules of a chemical reaction are called products
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Chemical reactions occur all the time all around us. Rusting of a car, cooking a meal, burning a fire, running your car on gasoline.
2.16 CONNECTION: Acid precipitation and ocean acidification threaten the environment
When we burn fossil fuels (gasoline and heating oil), air-polluting compounds and CO2 are released into the atmosphere
– Sulfur and nitrous oxides react with water in the air to form acids
– These fall to Earth as acid precipitation, which is rain, snow, or fog with a pH lower than 5.6
– Additional CO2 in the atmosphere contributes to the “greenhouse” effect and alters ocean chemistry
Copyright © 2009 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
Consider the statement:
“It’s paranoid and ignorant to worry about industry or agriculture contaminating the environment with their chemical wastes. After all, this stuff is just made of the same atoms that were already present in our environment anyway.”
What do you think of this statement?