Unit 2: Atomic Structure and the Periodic Table Vocabulary

Vocabulary practice flashcards covering atomic structure, subatomic particles, models of the atom, pure substances, mixtures, and periodic table organization.

Atom

The basic building block of all matter. It is the smallest particle of an element that still has the properties of that element.

Nucleus

The small, dense center of an atom. It contains protons and neutrons and holds almost all of the atom's total mass.

Proton

A positively ($+$) charged particle in the nucleus. The number of protons determines the identity of the atom.

Neutron

A particle found inside the nucleus that has no electrical charge (neutral). Neutrons add mass to the atom.

Electron

A negatively ($-$) charged particle found in the electron cloud outside the nucleus. Electrons have a mass much smaller than that of a proton or neutron.

Electron Cloud

The region surrounding the nucleus where electrons are most likely to be found. Electrons do not travel in fixed, perfect paths.

Bohr Model

A simplified model showing electrons placed on circular energy levels (rings) around the nucleus. The rings are a model, not actual electron paths.

Valence Electron

An electron located in the atom's outermost energy level. Valence electrons help explain how elements react and bond with other atoms.

Isotope

Atoms of the same element that have the exact same number of protons, but different numbers of neutrons.

Pure Substance

Matter that has a fixed, uniform chemical makeup throughout. Elements and compounds are both pure substances.

Element

A pure substance made of only one type of atom. It cannot be broken down into simpler substances by ordinary chemical changes.

Compound

A pure substance made of two or more different elements chemically bonded together in a fixed ratio.

Mixture

Two or more substances combined physically. The parts keep their own identities and can be separated.

Solution

A mixture where one substance dissolves completely and evenly into another, such as salt dissolved in a glass of water.

Periodic Table

An organized chart of chemical elements arranged in order of increasing atomic number that shows repeating patterns in their properties.

Atomic Number

The number of protons in an atom’s nucleus. Each element has a different atomic number.

Atomic Mass

The weighted average mass of all naturally occurring isotopes of an element, based on the combined mass of their protons and neutrons.

Chemical Symbol

A one- or two-letter abbreviation for an element. The first letter is capitalized; the second, if present, is lowercase.

Group (Family)

A vertical column on the periodic table. Elements in the same group share similar chemical properties and valence electrons.

Period

A horizontal row on the periodic table. As you move from left to right across a period, atomic numbers increase.

Metal

An element that is typically shiny, bends easily without breaking (malleable), and conducts heat and electricity well. Found on the left side of the periodic table.

Nonmetal

An element that conducts heat and electricity poorly. Solid nonmetals are dull and brittle; many nonmetals are gases. Found on the right side of the periodic table.

Metalloid

An element that has some properties of metals and some of nonmetals. Found along the zigzag stair-step line on the periodic table. Many metalloids are semiconductors used in electronics.