Atomic Structure & Theories

Ancient Greek philosopher who first proposed that matter was composed of indivisible particles called 'atomos'.

Elements are made of atoms, atoms of an element are identical, atoms of different elements combine to form compounds, and chemical reactions rearrange atoms.

J.J. Thomson's model of the atom, picturing a sphere of positive charge with negatively charged electrons embedded.

Rutherford discovered that the atom's positive charge and most of its mass are concentrated in a tiny, dense nucleus.

Niels Bohr proposed that electrons orbit the nucleus in fixed energy levels.

The central, dense part of an atom, containing protons and neutrons.

Particles smaller than an atom, such as protons, neutrons, and electrons that make up an atom.

A very small unit of mass used to describe the mass of atoms and subatomic particles (e.g., protons, neutrons).

Positively charged particles consisting of protons.

Negatively charged particles consisting of electrons.

High-energy rays with no charge.

The number of protons in an atom's nucleus.

The total number of protons and neutrons in an atom's nucleus.

A negative charge, approximately -1.602 x 10^-19 Coulombs.

Negligibly small compared to proton and neutron masses

A positive charge, approximately +1.602 x 10^-19 Coulombs.

A chemical compound always contains the same elements in the same proportions by mass, regardless of its source or method of preparation.

A group of two or more atoms held together by chemical bonds. These atoms can be of the same element or different elements.

A molecule composed of only two atoms. These atoms can be the same element or different elements.

A molecule composed of more than two atoms, which can be combinations of two or more different elements.

An ion with a positive charge, formed when a neutral atom loses one or more electrons.

An ion with a negative charge, formed when a neutral atom gains one or more electrons.

An ion containing only one atom, formed by the loss or gain of electrons from a neutral atom.

An ion composed of two or more atoms, where these atoms combine to form a unit with a net positive or negative charge.

A compound that has a specific number of water molecules attached to it.

Follow the general rules of chemical compound naming, and use prefixes for the number of water molecules.

A unit used for extremely large numbers of particles, like atoms or molecules.

The number of particles in one mole, approximately 6.022 × 10^23.

The mass in grams of one mole of a substance.

A chart organizing elements by their properties and atomic number.

Elements that are good conductors of heat and electricity.

Elements that are poor conductors of heat and electricity.

Horizontal rows on the periodic table organized by increasing atomic number, representing the number of electron orbitals.

Vertical columns on the periodic table organized by similar chemical properties, indicating the same number of valence electrons.

Group 2 elements, known for being reactive, good conductors, having a low density, and readily losing two electrons in reactions.

Groups 3-11 elements, characterized by multiple oxidation states, high conductivity, metallic properties, and often form colorful compounds.

Rare earth metals with one valence electron in the 5d shell, known for their high reactivity and silvery appearance.

Rare earth metals, highly reactive, radioactive, and exhibit paramagnetic, pyromorphic, and allotropic properties.

Elements with properties of both metals and nonmetals, like semiconductors and brittle.

The distance between the nuclei of two bonded identical atoms, representing the size of an atom.

Elements within the same period share the same number of electron orbitals, increasing as you move down the periodic table.

The minimum amount of energy required to remove the outermost electron from a neutral, gaseous atom in its ground state.

The energy change that occurs when a neutral atom in the gaseous state gains an electron.

Ionization energy generally increases across a period and decreases down a group on the periodic table.

Electron affinity generally increases across a period and decreases down a group on the periodic table.

Describes the arrangement of electrons in the energy levels and orbitals of an atom.

Electron configuration is used to determine valency, predict properties of elements, and interpret atomic spectra.

The energy required to remove the first electron from a neutral atom.

The energy required to remove subsequent electrons from an ion.