Atomic Theory, Atomic Forms, electron configuration, and Periodicity

Atomic theory

The atomic theory was developed by many people throughout time, including Democritus, Aristotle, Dalton, Thomson, Rutherford, and Bohr.

Democritus

An Ancient Greek philosopher who discovered there was a limit to how many times matter can be divided and named the smallest piece of matter 'Atomos.'

Atomos

Means divided or indivisible, as named by Democritus.

Dalton

A teacher who brought back Democritus's idea and proposed that substances are made up of atoms.

Law of multiple proportions

Dalton's data indicating that elements combine in specific ratios.

J.J. Thomson

Discovered that atoms are made of smaller negatively charged particles called electrons.

Plum pudding model

Thomson's model of the atom, where atoms are made of a positively charged substance with negative electrons scattered around.

Ernest Rutherford

Awarded the Nobel Prize in chemistry for discovering alpha particles and conducting the 'Gold foil experiment.'

Gold foil experiment

Rutherford's experiment that showed most of the matter in an atom is found in a very small part called the nucleus.

Bohr model

Proposed that electrons move in paths at certain distances around the nucleus.

Modern theory of the atom

States that electrons travel in regions called 'electron clouds' and their exact location cannot be predicted.

Energy levels

The energy an electron has is based on its location around the nucleus.

Quantum model

States that electrons do not orbit the nucleus but are located in orbitals.

Orbital

Quantum group states that have similar spatial shapes.

Isotopes

Atoms of the same element that have different numbers of neutrons in the nucleus.

Ions

Atom or molecule with an overall positive or negative charge.

Electron configuration

Represents the number of energy levels in an atom.

Pauli exclusion principle

States that each orbital can hold a maximum of two electrons.

Aufbau principle

States that electrons fill orbitals that have the lowest energy first.

Periodic table

A map of the building blocks of matter, organized in order of increasing atomic number.

Periodic law

States that properties of the elements are a function of their atomic number.

Atomic radius

The half distance between nuclei of identical atoms that are bonded together.

Ionization energy

The amount of energy required to remove a valence electron from a neutral atom.

Electronegativity

The energy release when an electron is added to an atom; a measure of the attraction of electrons.

Metallic character

Depends on the ability of an element to lose its outermost valence electrons.

Valence bond theory (octet rule)

Atoms tend to gain, lose, or share electrons to acquire a full set of eight valence electrons.

Anions

Atoms that gain electrons, making them negative ions.

Cations

Atoms that lose electrons, making them positive ions.

Chemical reactivity

Describes how easily an atom can lose or gain electrons.