Biology Chapter 2: Nature of Molecules and Water

Questions and Answers

What is the defining characteristic of matter?

Matter has mass and occupies space. (correct)

Matter has no mass and does not occupy space.

Matter can be broken down into smaller substances.

Matter consists only of solid substances.

Which subatomic particles are located in the nucleus of an atom?

Protons and electrons

Protons and neutrons (correct)

Neutrons and electrons

Electrons and positions

What is the atomic number of an element?

The number of protons in the nucleus (correct)

The number of neutrons in the nucleus

The number of electrons in a neutral atom

The total number of subatomic particles in the atom

How does an ion differ from a neutral atom?

An ion has an imbalance between protons and electrons. Signup and view all the answers

What does atomic mass refer to?

The sum of protons and neutrons in an atom Signup and view all the answers

What type of charge does a cation carry?

Positive charge Signup and view all the answers

What distinguishes an element from other substances?

It cannot be broken down into other substances by ordinary chemical means. Signup and view all the answers

How is weight different from mass?

Weight refers to the force gravity exerts on a substance, while mass refers to the amount of substance. Signup and view all the answers

What distinguishes isotopes of the same element from one another?

Different numbers of neutrons Signup and view all the answers

What term describes the time it takes for half of a sample of radioactive isotopes to decay?

Half-life Signup and view all the answers

In the Bohr model, how are electrons represented?

In fixed circular orbits Signup and view all the answers

What describes the potential energy of electrons in relation to their position?

Electrons farther from the nucleus have more potential energy Signup and view all the answers

What is the difference between energy levels and orbitals?

Energy levels are drawn as rings, orbitals have various shapes Signup and view all the answers

What is oxidation in the context of redox reactions?

Loss of an electron Signup and view all the answers

What does the octet rule suggest about atoms?

Atoms tend to have full outer energy levels Signup and view all the answers

Which of the following elements makes up the largest percentage of human body weight?

Carbon Signup and view all the answers

Which statement regarding valence electrons is true?

Inert elements have a full valence shell of eight electrons Signup and view all the answers

How are elements in the periodic table primarily arranged?

According to their valence electrons Signup and view all the answers

What defines the formation of ionic bonds?

Attraction between oppositely charged ions Signup and view all the answers

What is the characteristic of covalent bonds?

Form through the sharing of electrons Signup and view all the answers

What distinguishes polar covalent bonds from nonpolar covalent bonds?

Polar covalent bonds involve unequal sharing of electrons. Signup and view all the answers

What type of bond is primarily responsible for water's high surface tension?

Hydrogen bonds Signup and view all the answers

Which of the following factors does NOT influence the extent of a chemical reaction?

Electric charge of reactants Signup and view all the answers

What is the main reason for water's ability to act as a solvent for many substances?

Water has high polarity and can form hydrogen bonds. Signup and view all the answers

What is the term for the weak and non-directional attractive forces between atoms that are very close to one another?

Van der Waals forces Signup and view all the answers

Which property allows water to exhibit cohesion?

Hydrogen bonding between water molecules Signup and view all the answers

What type of reaction involves a shift of atoms from one molecule to another without a change in their identity?

Chemical reaction Signup and view all the answers

What role does electronegativity play in bond formation?

Dictates how electrons are shared in covalent bonds Signup and view all the answers

What is the significance of hydrogen bonding in water?

It contributes to water's high specific heat. Signup and view all the answers

What occurs when a water molecule exhibits adhesion?

Water molecules stick to other polar molecules. Signup and view all the answers

What happens to the charge distribution in a water molecule?

Hydrogen atoms become partially positively charged. Signup and view all the answers

Which process involves the breaking and forming of chemical bonds?

Chemical reaction Signup and view all the answers

What is the effect of water's high specific heat on organisms?

It stabilizes the temperature, minimizing changes. Signup and view all the answers

What happens during the evaporation of water?

It causes cooling of the surface from which water evaporates. Signup and view all the answers

Why does ice float on water?

Because ice has a lower density than liquid water. Signup and view all the answers

What property of water allows it to dissolve polar molecules and ions effectively?

Its hydrogen bonding capability. Signup and view all the answers

What occurs when an acid dissociates in water?

It increases the concentration of hydrogen ions. Signup and view all the answers

What is the role of buffers in biological systems?

To release hydrogen ions when an acid is added. Signup and view all the answers

What defines a substance as being neutral in terms of pH?

It has an equal concentration of hydrogen and hydroxide ions. Signup and view all the answers

How do biological membranes utilize the unique properties of water?

By utilizing hydrophobic interactions to create a barrier. Signup and view all the answers

What characteristic of water contributes to its ability to stabilize temperature changes in the environment?

High specific heat. Signup and view all the answers

How do hydrophobic compounds behave in water?

They are repelled by water and aggregate. Signup and view all the answers

Study Notes

Matter and Atoms

Matter has mass and occupies space, composed entirely of atoms.
Atoms consist of protons, neutrons (both in the nucleus), and electrons (in orbitals).

Atomic Structure

Protons are positively charged; neutrons are neutral; electrons have a negative charge.
The atomic number indicates the number of protons, which equals the number of electrons in a neutral atom.
Elements cannot be broken down by ordinary means; each has a unique atomic number.

Atomic Mass and Isotopes

Atomic mass is the sum of protons and neutrons; each has a mass of approximately 1 Dalton.
Isotopes differ in neutron number but maintain the same atomic number.
Radioactive isotopes decay over time (e.g., Carbon-14 has a half-life of 5730 years).

Electron Arrangement

Electron arrangement determines chemical behavior; electrons occupy orbitals around the nucleus.
Electrons farther from the nucleus possess higher potential energy.
Energy levels represent energy, while orbitals indicate the electron's probable location.

Chemical Bonds

Molecules consist of atoms bonded together; compounds contain different types of elements.
Ionic bonds form through the attraction between opposite charges (cations and anions).
Covalent bonds involve the sharing of electrons, satisfying the octet rule.

Electronegativity

Electronegativity is the affinity of an atom for electrons, leading to polar (unequal sharing) or nonpolar (equal sharing) covalent bonds.
Hydrogen bonds occur between polar molecules due to the attraction of electronegative atoms (e.g., oxygen).

Properties of Water

Water is crucial for life, with unique properties stemming from hydrogen bonding.
Cohesion and adhesion due to hydrogen bonds affect water movement in plants and organisms.
Water has a high specific heat and heat of vaporization, regulating temperature changes in environments.
Ice is less dense than liquid water, allowing aquatic life to survive under frozen surfaces.

Chemical Reactions

Involve the formation or breaking of chemical bonds, with reactants transforming into products.
Influenced by temperature, concentration, and catalysts; many reactions are reversible.

pH, Acids, and Bases

Water is neutral; pH measures hydrogen ion concentration.
Acids increase hydrogen ion concentration (lowering pH); bases combine with hydrogen ions (raising pH).
Buffers resist pH changes, maintaining homeostasis in biological systems.

Biological Buffers

Typically consist of an acid-base pair, contributing to the stability of pH in living organisms and biochemical processes.

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Description

Explore the fundamental concepts of molecules and the unique properties of water in this quiz based on Chapter 2 of Understanding Biology. This chapter provides vital insights into the foundational aspects of biological chemistry. Test your knowledge and understand how these elements influence life.