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Atomic Structure

A series of free High School Chemistry Video Lessons.

In these lessons, we will learn

  • Atomic Structure
  • Quantum Numbers
  • Atomic Emission Spectra
  • Atomic Number - Isotopes
  • Atomic Mass

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More High School Chemistry Lessons

Atomic Structure

The Bohr model is a simple model of atomic structure. It is now outdated, but is still useful at the basic level. An atom has a central core called its nucleus which contains its protons (positively charged particles) and neutrons (neutral particles). The Bohr model depicts electrons, tiny negatively charged particles, as orbiting the nucleus in concentric rings, representing energy levels. However, the electrons reside in atomic orbitals, which are more complicated.

The structure of the atom.
Basic Atomic Structure: A Look Inside the Atom
What does the inside of an atom look like? Here, we'll look at the subatomic particles ( protons, neutrons, and electrons) that make up the atom. We'll see how the electrons orbit the nucleus, and talk about the masses of protons, neutrons, and electrons in amu, or atomic mass unit.
The Structure of an Atom.

Mr. Andersen details the history of modern atomic theory.
This video describes atomic structure and tours the periodic table.


Quantum Numbers

All electrons have four quantum numbers which describe the location of electrons in the electron cloud of an atom. The principle quantum number (n) describes the size of the orbital the electron is in. The angular momentum quantum number (l) describes the shape of the orbital. The magnetic quantum number (ml) describes the orientation of the orbital in space while the electron spin number (ms) describes the direction that the electron spins on its own axis.
What are the four quantum numbers? This video gives their names, their letters and their possible values.
How to identify a specific electron in an atom's electron cloud using quantum numbers.
This video defines the 4 quantum numbers and then shows you how to find these numbers for the electron of highest energy in an atom.


Atomic Emission Spectra

Atomic emission spectra are unique spectra of light emitted by an element when electricity is run through it or when it is viewed through a prism. Because they are unique, they can act as an element's "fingerprint." An emissions spectrum looks like a set of colored lines on a black background as opposed to an absorption spectrum which looks like black lines on a colored background. The colors are visible portions of the electromagnetic spectrum.
Lecture on the Bohr model of the atom, atomic emission spectrum and how they apply to the real world. Understanding the atomic emission spectra.
Atomic Emission Spectra.

Atomic Number - Isotopes

Every element has a unique atomic number. The atomic number specifies how many protons an element has in its nucleus. In the periodic table of the elements, elements are arranged in order of ascending atomic number. Isotopes are atoms that have the same number of protons but different numbers of neutrons. Different isotopes have different nuclear stabilities.
The meaning and uses of atomic numbers.

What are Isotopes?

We'll learn about what isotopes are and how to write atomic number and mass number in isotope notation. We talk about a simple analogy with cars to explain this tutorial. Isotopes are versions of an atom or an element that have the same number of protons, but different numbers of neutrons. Isotopes and isotope notation are particularly important in nuclear chemistry.
Isotopes and Elements Practice Problems
In this video we'll look at how to determine, calculate and solve for atomic number, mass number, isotopes, net charge, protons, neutrons, and electrons. We'll determine what element an atom is by using the periodic table.


Atomic Mass

An element's atomic mass is the mass of one atom of that element, measured in atomic mass units (amu). An element's atomic mass in amu is equal to its molar mass in g/mol. Using atomic mass to understand isotopes.

What is atomic mass? It is a weighed average of the different isotopes of an element. It is sometimes referred to as atomic weight, relative atomic mass, or average atomic mass. We look at how to calculate and determine the weighed average of elements using atomic mass units.
How to Calculate Atomic Mass Practice Problems
How do you calculate atomic mass? You have to multiply the atomic weight of an atom (in amu, or atomic mass units) by the percent abundance expressed as a decimal. Then you add these together for all the isotopes of an atom.


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