2 - Chemical Context of Life

Vocabulary flashcards covering chemical elements, atomic structure, isotopes, electron configuration, and chemical bonding from the Biology Olympiad lecture notes.

Matter

Anything that takes up space and has mass, with a natural tendency to move toward the lowest possible state of potential energy.

Element

A substance that cannot be broken down to other substances by chemical reactions, with $92$ elements occurring in nature.

Trace elements

Elements required for an organism to live but only needed in very small quantities, such as iodine which is required at $0.15\,milligrams$ daily for the human thyroid.

Compound

A substance consisting of two or more different elements combined in a fixed ratio, possessing characteristics different from its constituent elements.

Atom

The smallest unit of matter that still retains properties of an element, composed mostly of empty space.

Neutrons

Subatomic particles that are electrically neutral and are packed together in the atomic nucleus.

Protons

Subatomic particles having one unit of positive charge, found in the atomic nucleus.

Electrons

Subatomic particles having one unit of negative charge that form a cloud-like structure around the nucleus.

Atomic nucleus

The center of an atom consisting of tightly packed protons and neutrons.

Dalton

A unit of measurement for atoms, subatomic particles, and molecules, equivalent to the atomic mass unit ($\text{amu}$).

Atomic number

The number of protons and electrons in a neutral element, written as a subscript to the left of the element's symbol, such as ${}_{2}\text{He}$.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Atomic mass

The total mass of an atom, represented as the weighted average of its naturally occurring isotopes; for example, ${}_{11}^{23}\text{Na}$ has an atomic mass of $22.9898\,daltons$.

Isotopes

Different atomic forms of the same element that have the same number of protons but different numbers of neutrons.

Radioactive isotope

An isotope in which the nucleus decays spontaneously, giving off particles and energy, often leading to a change in the number of protons.

Half-life

The time it takes for $50\%$ of a radioactive isotope to decay, a characteristic value unaffected by environmental variables.

Radiometric dating

The process by which scientists measure the ratio of different isotopes to calculate how many years have passed since a rock was formed or an organism was fossilized.

Energy

The capacity to cause change, such as by doing work.

Potential energy

The energy that matter possesses because of its location or structure, such as the energy electrons have due to their distance from the nucleus.

Electron shells

Fixed levels of potential energy where electrons can exist; the first shell holds a maximum of $2$ electrons and the second holds a maximum of $8$.

Valence electrons

Electrons that exist in the outermost shell of an atom.

Valence shell

The outermost electron shell of an atom which determines the atom's chemical behavior.

Inert

A term describing an atom with a complete valence shell, making it chemically unreactive.

Orbital

The $3D$ space where an electron is found $90\%$ of the time; for example, the first shell has a spherical $\text{1s}$ orbital.

Chemical bonds

Attractions that allow atoms with incomplete valence shells to interact and stay together.

Covalent bond

A strong chemical bond formed by the sharing of a pair of valence electrons by two atoms.

Molecule

Two or more atoms held together by covalent bonds.

Single bond

A chemical bond representing the sharing of one pair of valence electrons.

Double bond

A chemical bond representing the sharing of two pairs of valence electrons.

Valence

An atom's bonding capacity, which usually equals the number of electrons required to complete its outermost shell.

Electronegativity

The ability of an atom to attract shared electrons in a chemical bond toward itself.

Nonpolar covalent bond

A covalent bond where electrons are shared equally because the atoms have the same electronegativity.

Polar covalent bond

A covalent bond where electrons are shared unequally because one atom is more electronegative than the other.

Ions

Oppositely charged atoms or molecules resulting from the total transfer of an electron from one atom to another.

Cation

A positively charged ion.

Anion

A negatively charged ion.

Ionic bond

An attraction between cations and anions due to their opposite charges.

Ionic compounds

Compounds formed by ionic bonds, also known as salts, which do not consist of molecules but ratios of elements in a crystal.

Hydrogen bond

A weak noncovalent attraction between a hydrogen atom and an electronegative atom.

van der Waals interactions

Weak, short-range attractions between molecules or atoms caused by temporary shifts in electron density.

Electron density

A measure of the probability of finding an electron at a specific location.

Chemical reactions

The process of making and breaking chemical bonds leading to changes in the composition of matter.

Reactants

The starting materials in a chemical reaction.

Products

The resulting materials produced by a chemical reaction.

Chemical equilibrium

The point in a reaction where the forward and reverse reactions occur at the same rate and the relative concentrations of reactants and products stabilize.

Essential elements

The $20-25\%$ of natural elements needed for life, with $C$, $H$, $O$, and $N$ making up $96\%$ of living matter.