Chemistry Units 1–4: Atomic Structure, Nuclear Radiation, and Periodic Trends

Comprehensive vocabulary flashcards covering atomic structure, subatomic particles, Dalton's atomic theory, nuclear radiation types and penetration, periodic table periods and groups, valence electrons, ions, and element categories.

Atomic Number

The number of protons in an element, which never changes and defines the identity of the element.

Mass Number

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

Atom

The smallest particle of an element that retains the chemical properties of that element; it consists of a nucleus with protons and neutrons, electrons surrounding the nucleus in space, and is composed mostly of empty space.

Protons ($p^+$)

Subatomic particles located in the atomic nucleus that possess a positive ($+$) electrical charge.

Electrons ($e^-$)

Subatomic particles located in the space surrounding the nucleus that carry a negative ($-$) electrical charge.

Neutrons ($n^0$)

Subatomic particles situated in the nucleus that carry no electrical charge.

Chemical Elements

Pure substances that cannot be decomposed into other substances by ordinary chemical means.

Dalton's Atomic Theory

A foundational chemical theory summarizing that: 1. Matter is composed of indivisible particles (atoms); 2. All atoms of a particular element are identical; 3. Different elements have different atoms; 4. Atoms combine in whole-number ratios; 5. In chemical reactions, atoms are merely rearranged, never created, destroyed, or transformed into atoms of other elements.

Alpha Particle ($^4_2\alpha$ or $^4_2\text{He}$)

A type of nuclear radiation with a weak positive charge ($+2e$), mass notation of $^4_2$, and low penetrating power.

Beta Particle ($^0_{-1}\beta$ or $^0_{-1}e^-$)

A type of nuclear radiation with a medium negative charge, mass-charge notation of $^0_{-1}$, which penetrates paper but is stopped by aluminium.

Gamma Radiation ($\gamma$)

High-energy nuclear radiation characterized by strong penetrating power, no mass, and no electrical charge ($0/0$).

Penetrating Power of Radiation

The relative ability of radiation to pass through shielding: alpha ($\alpha$) is stopped by paper, beta ($\beta$) passes through paper but is blocked by aluminium, and gamma ($\gamma$) passes through both and is absorbed or attenuated by thick lead.

Period

A horizontal row on the periodic table; all elements located within the same period contain the same number of electron energy levels or shells.

Group (Family)

A vertical column on the periodic table; elements in the same group possess the same number of valence electrons in their outer shell and exhibit similar chemical and physical properties.

Valence Electrons

Electrons located in the highest occupied principal energy level (outer shell) of an atom that govern the element's chemical behavior.

Ion

An atom or group of atoms with an electrical charge, formed when an atom gains electrons (yielding a negative charge) or loses electrons (yielding a positive charge).

The Periodic Law

A law understood by Mendeleev stating that when elements are arranged in order of increasing atomic number, they display a regular and repeating pattern of physical and chemical properties.

Metals

Elements found on the left side of the periodic table that are malleable, ductile, lustrous (shiny), good conductors of heat and electricity, and mostly solid at room temperature.

Nonmetals

Elements found near the right side of the periodic table that are dull, brittle, non-conductors, mostly solid or gas at room temperature, with bromine occurring as a liquid.

Metalloids

Semi-metals situated along the right side of the periodic table that possess properties of both metals and nonmetals; they are shiny yet brittle and function as semiconductors.

Alkali Metals

The metallic elements situated in Group 1 of the periodic table, each possessing $1$ valence electron.

Alkaline Earth Metals

The metallic elements situated in Group 2 of the periodic table, each possessing $2$ valence electrons.

Transition Metals

The large central block of metallic elements situated between the main groups of the periodic table.

Halogen Group

The elements belonging to Group 7 of the periodic table with $7$ valence electrons; predominantly nonmetals, with the last member classified as a metalloid.

Noble Gases

The stable nonmetal elements in Group 8 of the periodic table with full outer shells ($8$ valence electrons).