Lecture 1: Class Introduction and the Chemistry of Water

Comprehensive practice flashcards covering Lecture 1 on the chemical properties of water, atomic structure, ionic and covalent bonding, and acid-base chemistry.

What percentage of the human body is composed of water?

Approximately $70\%$

What is evaporative cooling and how does it function in humans?

Evaporative cooling occurs when sweat evaporates from the skin, carrying away heat energy. It functions because water molecules are polar and stick together via hydrogen bonds, requiring a large amount of energy to separate and evaporate.

What single chemical property of water gives rise to all of its biologically relevant properties?

Polarity

What is the structural definition of a polar molecule?

A molecule that has a slightly positive ($\delta+$) end and a slightly negative ($\delta-$) end due to unequal sharing of electrons.

What is the difference between cohesion and adhesion in water?

Cohesion is the attraction between water molecules themselves due to hydrogen bonds, whereas adhesion is the attraction between water molecules and other types of molecules.

Why is water considered an effective universal solvent?

Because water is polar, allowing it to dissolve ionic compounds (such as table salt, $NaCl$) and other polar molecules (such as sugar).

Why does ice float on liquid water, and what biological advantage does this provide?

When water freezes, lattice-like structures form that make ice less dense than liquid water. Ice floating creates a protective top layer that prevents plants and animals beneath the ice from freezing solid.

What is the key difference between covalent bonds and ionic bonds?

Covalent bonds involve the sharing of electrons between atoms, whereas ionic bonds involve one atom stealing/donating electrons to another, creating oppositely charged ions that attract each other.

What distinguishes polar covalent bonds from nonpolar covalent bonds?

In polar covalent bonds, electrons are shared unequally and stay closer to one atom's nucleus. In nonpolar covalent bonds, electrons are shared equally between the atoms.

What subatomic particle determines an element's atomic number?

Protons, which are positively charged particles located in the nucleus with a mass of $1$.

How is the atomic mass of an element calculated?

By adding the number of protons and neutrons in the nucleus of an atom.

What are the charge, mass, and location of an electron?

An electron is a negatively charged particle that travels around the nucleus and has negligible mass.

How many protons and electrons are in a neutral Sodium ($Na$) atom?

$11$ electrons and $11$ protons.

How many protons and electrons do neutral atoms of Oxygen ($O$), Nitrogen ($N$), and Carbon ($C$) contain?

Oxygen has $8$ electrons and $8$ protons; Nitrogen has $7$ electrons and $7$ protons; Carbon has $6$ electrons and $6$ protons.

According to the rules for drawing Bohr model energy levels, how many electrons can occupy Levels 1, 2, and 3?

Level 1 can hold up to $2$ electrons, Level 2 can hold up to $8$ electrons, and Level 3 can hold up to $8$ electrons.

How do acids and bases alter the concentration of hydrogen ions ($H^+$) in water?

Acids increase the concentration of $H^+$ ions when dissolved in water, while bases decrease the concentration of $H^+$ ions (often by releasing $OH^-$ ions).

What is the numerical range of the pH scale, and what is the typical pH of human body fluids?

The pH scale ranges from $0$ (most acidic) to $14$ (most basic), with $7$ being neutral; human body fluids have a pH of $7.4$.

What is a chemical buffer, and what molecule acts as a buffer in the human body?

A buffer absorbs excess $H^+$ or $OH^-$ to maintain a stable pH (usually composed of a weak acid and weak base); in the human body, $CO_2$ acts as a buffer.