Chapter 2 Quiz 1.One of the four most common elements in living organisms is? 2.What trace element...

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

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

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

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

Electroncloud

Protons

2e–Nucleus

Electrons

Massnumber = 4Neutrons

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

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

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

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

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

A Goiter in a Malaysian woman, a symptom of iodine deficiency.

Ex. Good additive

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.

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

Magnesium

Lithium

Hydrogen

Thirdshell

Firstshell

Secondshell

Sodium

Beryllium

Aluminum

Silicon

Carbon

Phosphorus

Nitrogen

Sulfur

Oxygen

Chlorine

Fluorine

Helium

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

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

Magnesium

Lithium

Hydrogen

Thirdshell

Firstshell

Secondshell

Sodium

Beryllium

Aluminum

Silicon

Carbon

Phosphorus

Nitrogen

Sulfur

Oxygen

Chlorine

Fluorine

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

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

Single

Double

Nonpolar

Hydrogen

Types of chemical bonds to know

Covalent

Single

Double

Nonpolar

Hydrogen

Covalent

Single

Double

Nonpolar

Hydrogen

Sharing of electrons

Water is another example of covalent bonds

Question

A hydrogen atom contains one electron. How many covalent bonds can it form?

Covalent

Single

Double

Nonpolar

Hydrogen

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

Covalent

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

Nonpolar

Hydrogen

Single bond

Double bond

Covalent

Single

Double

Nonpolar

Hydrogen

• 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

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”

Important Example

(+)(+)

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

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

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

(–) (–)

(+) (+)

Covalent

Single

Double

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

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

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

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

• 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

See-saw of ions

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

The starting molecules of a chemical reaction are called reactants

The final molecules of a chemical reaction are called products

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

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?

Chapter 2 Quiz 1.One of the four most common elements in living organisms is? 2.What trace element...

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