science test

Antoine Lavoisier

Early chemist who organized known elements into basic categories: metals, nonmetals, gases, and earths.

Dmitri Mendeleev

Chemist who arranged elements by increasing atomic mass and left empty spaces to predict the properties of undiscovered elements.

Periodic Law

Principle stating that when elements are arranged by increasing atomic number, their properties repeat in a regular, periodic pattern.

Proton

Positively charged subatomic particle found inside the nucleus.

Neutron

Neutral subatomic particle with no electric charge found inside the nucleus.

Electron

Negatively charged subatomic particle located outside the nucleus.

Nucleus

Dense center of an atom containing protons and neutrons, housing almost all of the atom's mass.

Atomic Number

The total number of protons in an atom, which uniquely identifies an element.

Mass Number

The total count of protons plus neutrons in an atom's nucleus.

Neutron Calculation Formula

$$\text{Neutrons} = \text{Mass Number} - \text{Atomic Number}$$

Isotopes

Atoms of the same element that have identical numbers of protons but different numbers of neutrons.

Nuclear Notation

Symbolic representation displaying mass number on top left, atomic number on bottom left, followed by the element symbol (e.g., ${}^{12}_{6}\text{C}$).

Excited State

The state of an electron after absorbing energy and jumping to a higher energy level.

Photon

A particle of light released when an electron releases energy and returns to a lower energy level.

Valence Electrons

Electrons located in the outermost energy level that determine an element's chemical reactivity and bonding.

Periods

The $7$ horizontal rows across the periodic table.

Groups (Families)

The $18$ vertical columns on the periodic table containing elements with similar chemical properties.

Alkali Metals

Group $1$ highly reactive metals with $1$ valence electron that readily form $+1$ ions.

Alkaline Earth Metals

Group $2$ reactive metals with $2$ valence electrons that typically form $+2$ ions.

Transition Metals

Metallic elements located in Groups $3$ through $12$ in the middle of the periodic table.

Metalloids

Elements with properties intermediate between metals and nonmetals, often used as semiconductors.

Halogens

Group $17$ nonmetals with $7$ valence electrons that react strongly with metals to form salts.

Noble Gases

Group $18$ unreactive gaseous elements with complete outer energy levels.

Strong Nuclear Force

Powerful, short-range fundamental force holding protons and neutrons together in the nucleus.

Electromagnetic Force (in nucleus)

Long-range force causing positively charged protons to repel each other.

Radioactivity

The process by which an unstable atomic nucleus decays, emitting radiation and particles.

Atomic Radius Trend

Periodic trend where atomic size increases going down a group and left across a period (largest at bottom-left).

Ionization Energy Trend

Periodic trend where energy needed to remove an electron increases going up a group and right across a period (largest at top-right).