Atomic Structure and Basic Chemistry Vocabulary (Biology Lecture)

A set of vocabulary flashcards covering core concepts from the lecture notes on atomic structure, shells, valence, reactivity, and basic chemical concepts relevant to biology.

Atom

The basic unit of a chemical element, consisting of a nucleus and electrons around it.

Nucleus

The dense center of an atom that contains protons (positive) and neutrons (neutral).

Proton

A positively charged subatomic particle in the nucleus that determines the element’s identity (atomic number).

Neutron

A neutral subatomic particle in the nucleus that contributes to atomic mass.

Electron

A negatively charged subatomic particle that orbits the nucleus; has negligible mass but determines chemical behavior.

Atomic Number

The number of protons in the nucleus; identifies the element.

Atomic Mass (Atomic Weight)

The total number of protons and neutrons in the nucleus; averaged over naturally occurring isotopes.

Dalton

A unit of atomic mass used for atoms and subatomic particles.

Isotope

Atoms of the same element with different numbers of neutrons and thus different masses.

Electron Shell / Energy Level

Regions around the nucleus where electrons reside; shells have capacity limits.

First Energy Shell

Innermost electron shell; maximum of two electrons.

Second Energy Shell

Second electron shell; maximum of eight electrons in the simplified model.

Third Energy Shell

Outer shell for many biologically relevant elements; in this model often discussed with eight capacity.

Valence Shell

Outermost electron shell of an atom; its electrons determine reactivity.

Valence

Electrons in the outermost shell that participate in bonding; often described as the number of electrons needed to complete the shell.

Valence Electron

An electron in the valence shell involved in chemical bonding.

Orbital

A region within a shell where an electron is likely to be found; includes s and p types.

S Orbital

A spherical orbital in a shell that can hold up to two electrons.

P Orbitals

Three perpendicular, dumbbell-shaped orbitals in a shell that can hold up to two electrons each.

Noble Gases

Elements with full outer electron shells; generally nonreactive (inert).

Helium

A noble gas with a full outer shell (2 electrons); highly unreactive.

Neon

A noble gas with a full outer shell; nonreactive and famous for neon signs.

Argon

A noble gas with a full outer shell; nonreactive; often used as an inert atmosphere.

Chlorine

A highly electronegative element; tends to gain/attract electrons and is highly reactive.

Sodium

An alkali metal with a single electron in its outer shell; highly reactive and forms Na+ ions.

Ion

An atom or molecule that has gained or lost electrons, resulting in a net electrical charge.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Ionic Bond

A bond formed by transfer of electrons between atoms, creating oppositely charged ions that attract.

Sodium Chloride (NaCl)

Common table salt; formed when Na+ and Cl− combine to create a stable compound.

Hydrogen

A light, highly reactive element with 1 proton and 1 electron; often forms H2.

Electronegativity

The tendency of an atom to attract electrons in a chemical bond.

Density

Mass per unit volume; describes how compact a substance is and affects buoyancy and layering.

Reactivity (Reactivity of Elements)

The tendency of a substance to undergo chemical change; related to valence and electron arrangement.

Excited State

A higher-energy state of an electron after absorbing energy.

Ground State

The lowest-energy, most stable state of an electron, closest to the nucleus.