water properties

Matter

Anything that takes up space and has mass.

Element

A substance that cannot be broken down to other substances by chemical reactions.

Compound

A substance consisting of two or more different elements combined in a fixed ratio.

Emergent Properties

Novel characteristics that appear as a result of chemical combination, which are different from those of the component elements on their own.

Essential Elements

Chemical elements required by an organism to live a healthy life and reproduce (about 20–25% of the 92 natural elements).

Trace Elements

Elements required by an organism in only minute (very small) quantities to survive.

Atom

The smallest unit of matter that still retains the properties of an element.

Neutron

A subatomic particle with no electrical charge, located in the atomic nucleus.

Proton

A subatomic particle with a positive electrical charge, located in the atomic nucleus.

Electron

A subatomic particle with a negative electrical charge, moving in a cloud around the atomic nucleus.

Atomic Nucleus

The dense central core of an atom, containing protons and neutrons.

Dalton

The standard unit of measurement used to express the mass of subatomic particles and molecules (equivalent to an atomic mass unit, or amu).

Atomic Number

The total number of protons in the nucleus of an atom, unique to each element.

Mass Number

The sum of the number of protons plus neutrons in an atom's nucleus.

Atomic Mass

The total mass of an atom, which can be closely approximated by its mass number.

Isotopes

Atomic forms of an element that contain the same number of protons but differ in their number of neutrons, resulting in different mass numbers.

Radioactive Isotope

An unstable isotope whose nucleus decays spontaneously, shedding particles and energy.

Energy

The capacity to cause change.

Potential Energy

The energy that matter possesses because of its structural layout or physical location.

Electron Shells

The distinct energy levels where electrons are distributed, each at a characteristic average distance from the nucleus.

Valence Shell

The outermost electron shell of an atom.

Valence Electrons

The electrons occupying the outermost shell, which dictate the atom's chemical behavior.

Inert

Unreactive; the chemical state of an atom that has a completely full valence shell.

Chemical Bonds

Attractions that hold atoms together tightly, resulting from the sharing or transferring of valence electrons.

Covalent Bond

A strong chemical bond formed when two atoms share a pair of valence electrons.

Molecule

Two or more atoms held together securely by covalent bonds.

Single Bond

The sharing of exactly one pair of valence electrons between two atoms.

Double Bond

The sharing of two pairs of valence electrons between two atoms.

Structural Formula

A chemical formula that uses lines to represent shared electron bonds (e.g., $H-H$).

Molecular Formula

A formula indicating the exact type and number of atoms in a molecule (e.g., $H_2$).

Bonding Capacity (Valence)

The specific number of covalent bonds an atom can form, usually equal to the number of unpaired electrons needed to complete its valence shell.

Electronegativity

The measure of an atom's particular attraction for the shared electrons within a covalent bond.

Nonpolar Covalent Bond

A covalent bond in which electrons are shared completely equally between two atoms of similar electronegativity.

Polar Covalent Bond

A covalent bond between atoms that differ in electronegativity, pulling the shared electrons closer to the more electronegative atom and creating partial charges.

Ions

Atoms or molecules that have fully lost or gained one or more valence electrons, giving them an explicit electrical charge.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Ionic Bond

A chemical bond resulting from the electrostatic attraction between oppositely charged cations and anions.

Ionic Compounds (Salts)

Compounds formed entirely by ionic bonds, often arranging into crystalline configurations in nature.

Hydrogen Bond

A weak chemical interaction formed when a hydrogen atom covalently bonded to an electronegative atom is attracted to another nearby electronegative atom.

Van der Waals Interactions

Weak attractions that occur between transiently positive and negative regions of nonpolar atoms or molecules when they are very close together.

Molecular Mimic

A synthetic molecule whose similar size and shape allow it to mimic a natural biological molecule and bind to the same cellular receptors.

Chemical Reactions

The chemical processes that make and break chemical bonds, altering the composition of matter.

Reactants

The starting materials or molecules in a chemical reaction.

Products

The final resulting materials or molecules produced by a chemical reaction.

Photosynthesis

The solar-powered chemical process that rearranges carbon dioxide and water molecules into glucose and oxygen.

Chemical Equilibrium

The dynamic state in a reversible reaction where the forward and reverse reaction rates balance out exactly, keeping reactant and product concentrations stable.

Polar Molecule

A molecule with an uneven distribution of charges, such as water, where oxygen holds a partial negative charge and hydrogens hold partial positive charges.

Cohesion

The phenomenon where a substance is held together by internal attractions, such as water molecules staying close together via hydrogen bonds.

Adhesion

The clinging of one substance to an entirely different substance, such as water adhering to plant cell walls.

Surface Tension

A precise measurement of how difficult it is to stretch or break the surface layer of a liquid.

Kinetic Energy

The explicit energy associated with the relative motion of matter.

Thermal Energy

A measure of the total amount of kinetic energy due to the random movement of atoms or molecules within a body of matter.

Temperature

A measure of the average kinetic energy of the molecules in a body of matter, regardless of volume.

Heat

Thermal energy in transfer from one body of matter to another.

Calorie (cal)

The amount of heat required to raise the temperature of $1\,g$ of water by exactly $1\,^\circ\text{C}$.

Kilocalorie (kcal)

A unit of heat energy equal to $1{,}000\text{ calories}$; the "calories" noted on food packaging.

Joule (J)

A standard unit of energy, where $1\text{ calorie}$ equals $4.184\,\text{Joules}$.

Specific Heat

The amount of heat that must be absorbed or lost for $1\,g$ of a substance to change its temperature by $1\,^\circ\text{C}$.

Evaporation (Vaporization)

The physical transformation of a substance from a liquid state into a gaseous state.

Heat of Vaporization

The exact quantity of heat that $1\,g$ of a liquid must absorb to be converted successfully into a gas.

Evaporative Cooling

The process in which the surface of a liquid cools down during evaporation because the molecules with the highest kinetic energy depart as gas.

Solution

A liquid state that constitutes a completely homogeneous mixture of two or more substances.

Solvent

The dissolving agent within a solution.

Solute

The specific substance that is dissolved within a solution.

Aqueous Solution

A solution in which water acts explicitly as the solvent.

Hydration Shell

The sphere of water molecules that surrounds each dissolved ion in an aqueous solution.

Hydrophilic

Having an affinity or attraction to water.

Hydrophobic

Having no affinity for water; tending to coalesce and repel water due to nonpolar characteristics.

Molecular Mass

The sum of the masses of all the individual atoms in a molecule.

Mole (mol)

The exact number of grams of a substance equal to its molecular weight in daltons, representing $6.02 \times 10^{23}$ (Avogadro's number) molecules.

Molarity (M)

A common unit of concentration measuring the total number of moles of solute dissolved per liter of solution.

Hydrogen Ion ($H^+$)

A single proton with a charge of $+1$, dissociated from a water molecule.

Hydroxide Ion ($OH^-$)

A water molecule that has lost a proton, leaving it with a net charge of $-1$.

Hydronium Ion ($H_3O^+$)

A water molecule that has secured an extra proton from a dissociated water molecule.

Acid

A substance that increases the hydrogen ion concentration of a solution.

Base

A substance that reduces