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Atomic Structure

A series of free High School Chemistry Video Lessons from Brightstorm.

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 It is now outdated, but is still useful at the basic level.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.

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.

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.

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.

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.

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