Section 2: Chemistry of Life
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98 Terms
four major elements that make up about 96% of living organisms?
Carbon, hydrogen, oxygen, and nitrogen (CHON).
Which six elements make up about 99% of living matter?
Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS).
What is an element?
A substance consisting of only one type of atom.
What is an atom?
The smallest unit of an element that retains its chemical properties.
What are the three subatomic particles?
Protons, neutrons, and electrons.
Which subatomic particle has a positive charge?
Protons.
Which subatomic particle has a negative charge?
Electrons.
Which subatomic particle has no charge?
Neutrons.
Where are protons located?
In the nucleus.
Where are neutrons located?
In the nucleus.
Where are electrons located?
In electron orbitals surrounding the nucleus.
Which subatomic particle determines the identity of an element?
Protons.
What is the atomic number?
The number of protons in an atom.
What is the mass number?
The total number of protons plus neutrons.
How do you calculate the number of neutrons?
Mass number − atomic number.
What is an isotope?
Atoms of the same element with different numbers of neutrons.
Do isotopes have different chemical properties?
Usually no, because they have the same number of electrons.
Why do isotopes differ in mass?
Because they contain different numbers of neutrons.
What is a radioactive isotope?
An unstable isotope that emits radiation as it decays.
What is a half-life?
The time required for half of a radioactive sample to decay.
Name one medical use of radioactive isotopes.
Medical imaging or cancer treatment.
What is an electron shell?
A region around the nucleus where electrons are likely to be found.
How many electrons fit in the first shell?
2.
How many electrons fit in the second shell?
8.
What are valence electrons?
Electrons in the outermost shell.
Why are valence electrons important?
They determine chemical bonding.
What is the octet rule?
Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.
What is a chemical bond?
An attraction that holds atoms together.
What are the three major types of chemical bonds in biology?
Covalent, ionic, and hydrogen bonds.
What is a covalent bond?
A bond formed by sharing electron pairs.
What is a single covalent bond?
Sharing one pair of electrons.
What is a double covalent bond?
Sharing two pairs of electrons.
Which is stronger: single or double covalent bonds?
Double covalent bonds.
What is a nonpolar covalent bond?
Equal sharing of electrons.
What is a polar covalent bond?
Unequal sharing of electrons.
What causes polarity?
Differences in electronegativity.
What is electronegativity?
An atom's attraction for shared electrons.
Which atom is highly electronegative and central to biology?
Oxygen.
Why is oxygen partially negative in water?
It attracts shared electrons more strongly than hydrogen.
Which end of a water molecule is partially positive?
The hydrogen atoms.
Which end of a water molecule is partially negative?
The oxygen atom.
What is an ion?
An atom or molecule with a net electric charge.
What is a cation?
A positively charged ion.
What is an anion?
A negatively charged ion.
How are cations formed?
By losing electrons.
How are anions formed?
By gaining electrons.
What is an ionic bond?
The attraction between oppositely charged ions.
Do ionic bonds remain intact in water?
Usually they dissociate.
Why do salts dissolve easily in water?
Water surrounds and stabilizes individual ions.
What is a hydrogen bond?
A weak attraction between a partially positive hydrogen and an electronegative atom.
Which atoms commonly participate in hydrogen bonding?
Oxygen, nitrogen, and fluorine.
Are hydrogen bonds stronger or weaker than covalent bonds?
Weaker.
Why are hydrogen bonds biologically important?
They stabilize DNA, proteins, and water.
Which bond is strongest?
Covalent bonds.
Which bond is weakest?
Van der Waals interactions.
What are van der Waals interactions?
Weak attractions caused by temporary fluctuations in electron distribution.
Why do geckos climb walls?
Millions of van der Waals interactions between their feet and surfaces.
What determines an atom's chemical behavior?
Its valence electrons.
Why are noble gases chemically unreactive?
Their outer shells are full.
Why is carbon so versatile?
It has four valence electrons and forms four covalent bonds.
How many covalent bonds can carbon form?
Four.
Why is carbon considered the backbone of life?
It forms stable chains and rings.
What is molecular formula?
The actual number of each type of atom in a molecule.
What is structural formula?
A diagram showing how atoms are connected.
Why is molecular shape important?
Shape determines biological function.
What is a molecule?
Two or more atoms joined by covalent bonds.
What is a compound?
A substance containing two or more different elements.
Can a molecule consist of only one element?
Yes, such as O₂.
Are all compounds molecules?
Yes, when formed by covalent bonds.
Why does NaCl not exist as discrete molecules?
It forms a crystal lattice of ions.
What is potential energy in atoms?
Energy stored because of electron position.
Why do electrons farther from the nucleus contain more potential energy?
They are less tightly held.
What happens when an electron moves to a lower energy level?
It releases energy.
What is chemical energy?
Potential energy stored in chemical bonds.
Why are electrons important in metabolism?
They carry energy during oxidation-reduction reactions.
What is oxidation?
Loss of electrons.
What is reduction?
Gain of electrons.
Remember OIL RIG.
Oxidation Is Loss; Reduction Is Gain (of electrons).
What is a redox reaction?
A reaction involving electron transfer.
Why are redox reactions essential in biology?
They power cellular respiration and photosynthesis.
What is an electron donor?
A substance that loses electrons.
What is an electron acceptor?
A substance that gains electrons.
What is cohesion?
Attraction between identical molecules.
What is adhesion?
Attraction between different molecules.
Why is polarity responsible for hydrogen bonding?
Partial charges attract each other.
Which bond holds together the atoms within a water molecule?
Polar covalent bonds.
Which bond holds neighboring water molecules together?
Hydrogen bonds.
IMAT trap: Do neutrons determine chemical behavior?
No. Valence electrons determine chemical behavior.
IMAT trap: Can isotopes have different numbers of protons?
No. Different proton numbers make different elements.
IMAT trap: Does gaining electrons make an atom more positive?
No. Gaining electrons makes it more negative.
IMAT trap: Are hydrogen bonds true chemical bonds?
No. They are weak intermolecular attractions.
IMAT trap: Which bond must be broken first when boiling water?
Hydrogen bonds, not covalent O-H bonds.
IMAT trap: Why is carbon uniquely suited for life?
It forms four stable covalent bonds, allowing enormous molecular diversity.
IMAT trap: Which particles are exchanged in ordinary chemical reactions?
Electrons only. Protons remain unchanged.
Clinical connection: Why is calcium (Ca²⁺) written with a 2+ charge?
It has lost two electrons.
Clinical connection: Why does sodium conduct electricity in solution?
Because Na⁺ ions move freely in water.
Clinical connection: Why does oxygen readily form hydrogen bonds?
It is highly electronegative and possesses lone electron pairs.
High-yield IMAT fact: Nearly every biological reaction depends on electron movement.
Redox reactions underlie ATP production, photosynthesis, and metabolism.