Atomic Theory Overview

A substance that cannot be broken down into simpler substances by chemical means or produced by combining simpler substances.

Horizontal rows on the periodic table where elements have the same number of electron shells.

Vertical columns on the periodic table where elements have the same number of electrons in their outermost shell (valence shell).

The number of electrons in an atom's outermost shell, which determines how many chemical bonds an element can form.

A rule that states that most atoms try to attain eight electrons in their outermost shell when they bond to achieve stability.

The smallest unit of an element that can exist independently and retain the chemical properties of that element.

A positively charged particle found in the nucleus of an atom.

A neutrally charged particle found in the nucleus of an atom.

A negatively charged particle that orbits the nucleus of an atom.

The central part of an atom where protons and neutrons reside.

The number of protons in an atom's nucleus.

The average mass of all known isotopes of an element.

Atoms of the same element with the same number of protons but different number of neutrons.

Elements with one electron in their outermost shell, making them highly reactive, soft metals with low densities. They tarnish quickly in air and react vigorously with water.

Elements with two electrons in their outermost shell, making them reactive, slightly less reactive than alkali metals. The most common example is Magnesium, which reacts slowly with water.

Elements with seven electrons in their outermost shell, making them highly reactive non-metals. They have low melting and boiling points and exist in different states of matter at room temperature: Fluorine and Chlorine are gases, Bromine is a liquid, and Iodine is a solid.

Elements with eight electrons in their outermost shell (except Helium, which has 2), making them extremely unreactive. They are gases at room temperature and their boiling points increase as you move down the group.

A measure of the total number of protons and neutrons in an atom's nucleus. This number can vary within an element, leading to isotopes.

The average atomic mass of an element, taking into account the relative abundance of its isotopes.

The average mass of a molecule of a compound compared to 1/12 the mass of the carbon-12 isotope, taking relative abundances of the naturally occurring isotopes into account.

Any element that forms a positive ion (cation) by losing electrons.

A non-metal that exists as a diatomic molecule at room temperature.

A positive ion formed when an atom loses one or more electrons.

A negative ion formed when an atom gains one or more electrons.

A chemical reaction that involves the loss of electrons from an atom.

A chemical reaction that involves the gain of electrons by an atom.

The number of protons in the nucleus of an atom, which determines the element's identity.

The weighted average of the masses of all the isotopes of an element, relative to the mass of carbon-12.

Atoms of the same element that have the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers.

A technique that separates ions based on their mass-to-charge ratio. It allows us to identify and measure the abundance of different isotopes.

A measure of the average mass of an element's atoms, taking into account the relative abundance of its isotopes.

The average mass of an atom of an element, calculated based on the masses and relative abundances of its isotopes.

A group of atoms held together by chemical bonds.

An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.