Chapter 2

Question 1

Atomic Mass

Answer 1

The total mass of an atom, equal to the number of protons + neutrons.

Question 2

Proton

Answer 2

A positively charged particle found in the atomic nucleus.

Question 3

Neutron

Answer 3

A neutral (no charge) particle found in the atomic nucleus.

Question 4

Electron

Answer 4

A negatively charged particle that orbits the nucleus in electron shells.

Question 5

Atomic Nucleus

Answer 5

The dense center of the atom that contains protons and neutrons.

Question 6

Element

Answer 6

A pure substance made of only one kind of atom.

Question 7

Atomic Number

Answer 7

The number of protons in an atom; identifies the element.

Question 8

Isotopes

Answer 8

Atoms of the same element with different numbers of neutrons.

Question 9

Isomers

Answer 9

Molecules with the same chemical formula but different structural arrangements.

Question 10

Valence Electrons

Answer 10

Electrons located in the outermost shell of an atom; determine chemical behavior.

Question 11

Covalent Bond

Answer 11

A bond formed when atoms share electrons.

Question 12

Electronegativity

Answer 12

An atom’s ability to attract electrons in a bond.

Question 13

Nonpolar Covalent Bond

Answer 13

A covalent bond where electrons are shared equally.

Question 14

Polar Covalent Bond

Answer 14

A covalent bond where electrons are shared unequally, creating partial charges.

Question 15

Polarity

Answer 15

The presence of uneven charge distribution in a molecule.

Question 16

Molecule

Answer 16

Two or more atoms bonded together.

Question 17

Ion

Answer 17

An atom or molecule that has gained or lost electrons and now has a charge.

Question 18

Ionic Bond

Answer 18

A bond formed when one atom transfers electrons to another, creating oppositely charged ions.

Question 19

Hydrogen Bond

Answer 19

A weak attraction between a partially positive hydrogen and a partially negative atom (like O or N).

Question 20

Solution

Answer 20

A uniform mixture of two or more substances.

Question 21

Solvent

Answer 21

The substance that dissolves the solute (e.g., water).

Question 22

Solute

Answer 22

The substance that is dissolved (e.g., salt).

Question 23

Hydrophilic

Answer 23

“Water-loving”; dissolves in or mixes well with water.

Question 24

Hydrophobic

Answer 24

“Water-fearing”; does not mix with water (like oil).

Question 25

pH

Answer 25

A measure of how acidic or basic a solution is.

Question 26

Acid

Answer 26

A substance that increases hydrogen ion (H⁺) concentration; pH < 7.

Question 27

Base (Alkaline)

Answer 27

A substance that decreases hydrogen ion concentration; pH > 7.

Question 28

Buffer

Answer 28

A system that resists changes in pH by absorbing or releasing H⁺.

Question 30

Define matter.

Answer 30

Anything that has mass and takes up space. ## Footnote Chemistry is crucial for biology as all living things are made of chemicals, and life processes are chemical reactions.

Question 31

Identify the four elements most abundant in living organisms.

Answer 31

* Carbon (C) * Hydrogen (H) * Oxygen (O) * Nitrogen (N) ## Footnote These four elements make up approximately 96% of living matter.

Question 32

Distinguish between electrons, neutrons, and protons.

Answer 32

* Protons: positive charge, in the nucleus * Neutrons: no charge, in the nucleus * Electrons: negative charge, orbiting the nucleus ## Footnote These subatomic particles have distinct roles in atomic structure.

Question 33

Explain the difference between **atomic number** and **mass number**.

Answer 33

* Atomic Number = protons * Mass Number = protons + neutrons ## Footnote Atomic number defines the element, while mass number indicates the total number of protons and neutrons.

Question 34

Use atomic number and mass number to determine the number of **neutrons**.

Answer 34

Neutrons = Mass Number – Atomic Number ## Footnote Example: Carbon has atomic number 6 and mass number 12 → 6 neutrons.

Question 35

What is the major difference between atoms of different **elements** (e.g., carbon vs. hydrogen)?

Answer 35

They have different numbers of protons. ## Footnote Proton number defines the element.

Question 36

Define **isotope** and give two biological applications of **radioactive isotopes**.

Answer 36

Isotope: atoms of the same element with different neutron numbers. Biological uses: * Medical imaging/tracing (e.g., PET scans) * Radiometric dating of fossils or rocks ## Footnote Tracing metabolic pathways in research is an additional application.

Question 37

Use **valence electrons** to predict ionic vs covalent bonds & ion formation.

Answer 37

Rule of thumb: * Metal + nonmetal → ionic bond * Nonmetal + nonmetal → covalent bond Ion formation prediction: * 1–3 valence electrons → forms a positive ion (cation) * 5–7 valence electrons → forms a negative ion (anion) ## Footnote Example: Sodium (1 valence e⁻) → loses 1 → Na⁺; Chlorine (7 valence e⁻) → gains 1 → Cl⁻.