Atomic Theory Cheat Sheet

Atomic theory explains that matter is composed of discrete units called atoms, which are the smallest building blocks of elements and retain their chemical identity. Understanding atomic structure, including protons, neutrons, and electrons, is fundamental to chemistry and physics.

Core Principles

All matter consists of atoms, indivisible particles that move in constant, random motion in a fluid.
Atoms of the same element are identical in form and mass, but differ from those of other elements.
Atoms cannot be created, destroyed, or subdivided.
Atoms combine in simple whole-number ratios to form compounds.
In chemical reactions, atoms are rearranged, combined, or separated.

Action Steps

1. Identify the element based on its atomic number (number of protons) to determine its fundamental properties.
2. Calculate the mass number by summing protons and neutrons to understand an isotope's mass.
3. Determine the number of neutrons by subtracting the atomic number from the mass number.
4. Calculate the charge of an ion by finding the difference between the number of protons and electrons.

Formulas

Atomic Number (Z): $Z = \text{number of protons}$
Mass Number (A): $A = \text{number of protons} + \text{number of neutrons}$
Number of Neutrons: $N = A - Z$
Charge of an Ion: $\text{Charge} = \text{number of protons} - \text{number of electrons}$

Key Terms

Atom: The basic unit of a chemical element, consisting of a nucleus (protons and neutrons) and surrounding electrons.
Proton: A subatomic particle with a positive electric charge, found in the nucleus of an atom.
Neutron: A subatomic particle with no net electric charge, found in the nucleus of an atom.
Electron: A subatomic particle with a negative electric charge, orbiting the nucleus.
Atomic Number (Z): The number of protons in the nucleus of an atom, defining the element.
Mass Number (A): The total number of protons and neutrons in an atom's nucleus.
Isotope: Atoms of the same element that have different numbers of neutrons (and thus different mass numbers).
Ion: An atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge.

Real World Examples

Determining the composition of a carbon-14 atom.: Knowing carbon has atomic number 6 (6 protons), and carbon-14 has a mass number of 14, you can deduce it has 8 neutrons (14 - 6 = 8) and is an isotope used in radiocarbon dating.
Understanding the formation of a sodium ion (Na+).: A neutral sodium atom has 11 protons and 11 electrons. To form a Na+ ion, it loses one electron, resulting in 11 protons and 10 electrons, giving it a net charge of +1.

Quiz

What defines an element?: Number of protons
An atom with 17 protons and 18 neutrons has a mass number of:: 35