BIOCHEMISTRY VOCAB

Element

A pure substance made of one type of atom. For example, oxygen (O) or gold (Au). Elements are the “letters” of the chemical alphabet.

Compound

A substance formed when two or more different elements chemically bond. For example, water (H₂O). Compounds are like “words” built from elements.

Protons

Positive charge, inside nucleus, define which element it is.

Neutrons

No charge, add mass and stability.

Electrons

Negative charge, orbit nucleus, control chemical behavior.

Atomic number

Number of protons in an atom. Each element has a unique one (carbon = 6).

Atomic nucleus

Dense center of the atom that contains protons + neutrons.

Atomic mass number

Total number of protons + neutrons. Example: Carbon-12 has 6 protons + 6 neutrons = 12.

Isotopes

Same element but different number of neutrons. (Carbon-12 vs Carbon-14).

Radioactive isotopes

Unstable isotopes that break down over time, releasing radiation. Useful in medicine and dating fossils.

Energy

Ability to do work or cause change (movement, heat, chemical reactions).

Potential energy

Stored energy. Example: a rock on a hill or electrons held in high energy levels.

Electron shells (energy levels)

Layers around the nucleus where electrons are found.

Octet rule

Atoms “want” 8 electrons in their outer shell (that makes them stable, like noble gases).

Valence electrons

Electrons in the outermost shell; these are the ones used in bonding.

Electronegativity

How strongly an atom pulls electrons. Example: Oxygen has high electronegativity, so in H₂O, it pulls electrons closer.

Ions

Atoms that gain or lose electrons and become charged (Na⁺, Cl⁻).

Salts

Ionic compounds (like NaCl) that form crystals and dissolve in water.

Covalent bond

Atoms share electrons (very strong).

Ionic bond

One atom transfers an electron to another, forming charged ions that attract.

Hydrogen bond

Weak bond between hydrogen and another electronegative atom (very important in water + DNA).

Nonpolar covalent bond

Electrons shared equally (like O₂ gas).

Polar covalent bond

Electrons shared unequally, causing partial charges (like H₂O).

Single bond

One pair of electrons shared (C–H).

Double bond

Two pairs shared (O=O).

Reactants

Substances you start with (on the left side of the arrow).

Products

Substances you end with (on the right side). Example: H₂ + O₂ → H₂O (reactants → product).

Buffer

A solution that resists changes in pH by absorbing or releasing H⁺ ions (important in blood).

Molarity

A measure of concentration: how many moles of solute per liter of solution.

Acid

Adds H⁺ ions to a solution, pH < 7 (ex: HCl).

Base

Removes H⁺ ions (or adds OH⁻), pH > 7 (ex: NaOH).

pH

Scale from 0–14 showing how acidic or basic something is (7 = neutral, pure water).

Cohesion

Water sticks to itself (droplets, surface tension).

Adhesion

Water sticks to other surfaces (why water climbs up glass).

Solvency

Water is the “universal solvent” because it dissolves many things. a substance that dissolves a solute, resulting in a solution

Surface tension

The “skin” on the surface of water due to cohesion.

Capillary action

Water moves up narrow tubes (plants use this to draw water up stems).

High specific heat

Water absorbs a lot of heat before changing temp, stabilizing climate.

High heat of vaporization

Takes a lot of heat to turn water into vapor → cooling effect (sweating).

Density as a solid

Ice is less dense than liquid water, so it floats (life survives under ice).

Hydration shell

A layer of water molecules around ions/polar molecules that keeps them dissolved.

Hydrophilic

Water-loving,” dissolves in water (salt, sugar).

Hydrophobic

“Water-fearing,” doesn’t dissolve (oil, fats).

Macromolecules

Big biological molecules: carbs, proteins, lipids, nucleic acids.

Monomers

Small building blocks (glucose, amino acids, nucleotides).

Polymers

Long chains of monomers linked together (starch, proteins, DNA).

Dehydration (condensation) reaction

Joins monomers together by removing water.

Hydrolysis

Breaks polymers apart by adding water.