topic 1: structure of water and hydrogen bonding

unit 1: chemistry inlife

matter

Matter is composed of atoms, which combine to form molecules and biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids)

element

a pure substance that cannot be broken down into simpler substances by chemical reactions. Each element is defined strictly by its atomic number (the specific number of protons in its nucleus).

Electronegativity

the measure of an atom's ability to attract shared electrons toward itself in a chemical bond

Atomic number

The number of protons in the nucleus of an atom, which determines the element's identity.

Atomic mass

The total mass of an atom, roughly calculated as the sum of its protons and neutrons.

Octet rule

the principle that atoms are most stable when their outermost electron shell holds eight electrons, leading them to share, gain, or lose electrons.

Chemical bonds

• The attractive forces that hold atoms together to form molecules and compounds, including covalent (sharing electrons), ionic (transferring electrons), and hydrogen bonds

Compound

: A substance made of two or more different elements combined in a fixed ratio (like h20)

Cohesion

The sticking together of like molecules (such as water molecules sticking to other water molecules via hydrogen bonds).

Adhesion

The sticking together of different types of molecules (such as water sticking to the inside of a glass tube).

Capillary action

• The upward movement of water through narrow spaces, driven by the combined forces of cohesion and adhesion.

Solvent

The dissolving agent of a solution; water is the universal solvent in biology.

Solute

: The substance that gets dissolved in a solvent (like salt or sugar

Solution

: A completely uniform, homogeneous mixture of a solvent and its dissolved solutes

pH

: A logarithmic measure of the hydrogen ion concentration (H^+) in a fluid, running on a scale from 0 (very acidic) to 14 (very basic)

Acid vs. Base

: An acid has a high concentration of \(\text{H}^{+}\) ions and a pH below 7, while a base (alkaline substance) has a low \(\text{H}^{+}\) concentration (or high \(\text{OH}^{-}\) hydroxide ions) and a pH above 7.

Buffer

: A chemical substance that minimizes pH changes in a solution by binding excess hydrogen ions or releasing them when levels drop