Atomic Structure

Atom

The smallest constituent unit of matter that possesses the properties of a chemical element, consisting of protons, neutrons, and electrons.

Molecule

A group of two or more atoms held together by chemical bonds, forming the smallest unit of a chemical compound.

Nucleus

The central part of an atom containing protons and neutrons.

Proton

Positively charged subatomic particle with a mass of approximately 1.672 × 10^-24 grams.

Neutron

Electrically neutral subatomic particle with a mass similar to a proton, approximately 1.674 × 10^-24 grams.

Electron

Negatively charged subatomic particle with a mass of approximately 9.1 × 10^-31 kilograms.

Atomic Number (Z)

The number of protons in an atom's nucleus, defining the element.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus, expressed in atomic mass units (u).

Isotope

Atoms of the same element with different numbers of neutrons, leading to variations in mass numbers.

Electron Configuration

The arrangement of electrons in energy levels or shells around the nucleus of an atom, following specific rules and principles.

Periodic Table

A tabular arrangement of elements based on their atomic number, electron configuration, and chemical properties.

Quantum Mechanical Model

Describes the behavior of electrons in atoms using orbitals and quantum numbers, replacing the Bohr model.

Periods

Horizontal rows in the periodic table indicating the highest energy level of electrons in an atom.

Groups

Vertical columns in the periodic table with elements sharing similar chemical properties and valence electrons.

Atomic Radius

The size of an atom, which decreases across a period and increases down a group in the periodic table.