Life, Chemistry, and Water — Practice Flashcards

A set of practice Q&A flashcards covering key concepts from the notes on elements, bonds, electronegativity, water properties, and basic biochemistry.

What four elements make up about 96% of the weight of living organisms, often abbreviated as CHON?

Carbon, Hydrogen, Oxygen, and Nitrogen (CHON).

Which elements make up about 4% of living organisms (Ca, P, K, Na, Cl, Mg, S)?

Calcium, Phosphorus, Potassium, Sodium, Chlorine, Magnesium, Sulfur.

What determines the chemical reactivity of an atom?

The arrangement of its valence electrons in the outermost energy level.

What are the four most important chemical linkages in biological molecules?

Ionic bonds, covalent bonds, hydrogen bonds, and van der Waals forces.

How does an ionic bond form?

By transfer of electrons from a metal to a nonmetal, forming cations and anions that attract each other.

What is the difference between a cation and an anion?

Cation is positively charged; anion is negatively charged.

What is a covalent bond?

A bond formed by sharing valence electrons between atoms (usually nonmetals).

What distinguishes nonpolar covalent bonds from polar covalent bonds?

Nonpolar covalent bonds share electrons equally; polar covalent bonds share electrons unequally due to differences in electronegativity.

What is electronegativity?

A measure of an atom's attraction for electrons in a bond; higher electronegativity means a stronger pull on shared electrons.

What are the typical electronegativity difference ranges for nonpolar, polar, and ionic bonds?

Nonpolar: 0.00–0.40; Polar: 0.50–1.70; Ionic: >1.70.

What is a hydrogen bond?

A weak attraction between a partially positive hydrogen atom and a partially negative atom (often O or N) in another molecule; collectively significant.

What are van der Waals forces?

Weak electrostatic forces between neutral molecules that operate over short distances and can stabilize biomolecules.

Why is water considered a polar molecule?

Oxygen is more electronegative than hydrogen, creating partial negative charge on O and partial positive charge on H.

List properties of water that are influenced by hydrogen bonding.

Density, specific heat, heat of vaporization, cohesion, adhesion, and surface tension.

Why is ice less dense than liquid water?

Ice forms a lattice with more open space, so fewer molecules fit in a given volume; ice is less dense and floats.

Why does water have a high specific heat and high heat of vaporization?

Hydrogen bonds retard molecular motion, so more energy is required to raise temperature or vaporize water.

What is cohesion?

Attraction between like molecules (water–water) due to hydrogen bonding.

What is surface tension?

The tendency of a liquid's surface to resist rupture under tension due to cohesive forces.

What is adhesion and capillary action?

Adhesion is attraction between unlike molecules; capillary action is the upward movement of water in narrow tubes due to adhesion and cohesion.

Why is water a good solvent for many biological substances?

Water’s polarity allows it to dissolve many polar and ionic compounds (and it can dissociate into H+ and OH−).

What does pH measure?

pH = -log[H+], the hydrogen ion concentration in a solution.

What is a buffer?

A substance that resists changes in pH by neutralizing added acids or bases.

What is the difference between a solvent and a solute?

Solvent is the substance dissolving the solute; solute is the substance being dissolved.

What is the difference between a molecule and a compound?

A molecule is two or more atoms held together by covalent bonds; a compound is a substance composed of two or more different elements.

What does CHON stand for?

Carbon, Hydrogen, Oxygen, and Nitrogen.

What is the role of carbon in organic molecules and molecular models?

Carbon is the building block of organic molecules and is central to molecular modeling due to its tetravalence.

How do polar vs nonpolar molecules relate to hydrophilicity and hydrophobicity?

Polar molecules are hydrophilic and interact with water; nonpolar molecules are hydrophobic and tend to avoid water.

What are the three subatomic particles that compose atoms?

Protons, neutrons, and electrons.