CONTENT IN A NUTSHELL

Atoms are composed of three smaller parts protons, neutrons, and electrons.
Protons are positively charged, neutrons have no charge, and electrons are negatively
charged. A neutral atom contains an equal number of protons and electrons. The
protons and neutrons together form the nucleus of the atom, occupying less than 0.01%
of the total atomic volume but accounting for 99.99% of the atomic mass. Electrons,
although contributing negligibly to the mass, spend their time in the remaining volume.
This means that most of the volume of an atom is essentially  nothingness. The number
of protons in the nucleus of an atom determines the element, but the electrons determine
the element’s chemical behavior. The outermost or valence electrons are those that can
be shared with other atoms to form molecules, or can be transferred to or from other
atoms, forming ionic salts. To understand how valence electrons determine the chemistry
of an element, the internal structure of the atom must be examined in greater detail.
Electrons occupy specific  spaces or energy levels in an atom. These energy levels
are quantized; the location of electrons in terms of energies (the electron configuration)
determines the nature and number of chemical bonds that each element forms. The
chemical and physical properties of an element are determined by its electron
configuration. These properties, the direct consequence of electron configuration, are
observed in such phenomena as fireworks, neon lights, television, and colorful fireplace
logs. In each instance, the distinctive colors are due to excitation of valence electrons.
 

PLACE IN THE CURRICULUM

This topic can be introduced early in the course and should precede modules on
Periodicity, Oxidation-Reduction, and Bonding. It requires the use of fairly abstract
concepts that may need additional reinforcement periodically in the course.
 

CENTRAL CONCEPTS

1. An atom is composed of a nucleus containing protons and neutrons, which is
surrounded by electrons. The electrons, though of little relative mass, occupy
most of the atomic volume.
2. Each electron and proton possesses the same absolute electrical charge
value, though of opposite sign. By convention, electrons are assigned a
negative charge (-) while protons are assigned a positive charge ( + ).
3. The atomic number represents the number of protons in the nucleus of an
atom. The mass number represents the sum of protons and neutrons in the
nucleus. The atomic mass is the weighted average of all naturally occurring
isotopes (same atomic number, different number of neutrons) of an element.
4. Light has a dual nature, behaving both as waves and particles. This behavior
is governed by several mathematical relationships:
 

 
 
5. Electrons have a dual nature, behaving both as waves and particles.
6. Electrons occupy specific energy levels in an atom. These energy levels are
quantized and are described by shells, subshells, and orbitals.
7. The orbital occupancy of a multi-electron atom is given by its electron
configuration. This electron configuration can be described as following
several empirical rulesHund’s rule, the Pauli exclusion principle, and the
aufbau principle.
8. The structure of the Periodic Table is a reflection of the electronic structure
of atoms.

 
RELATED CONCEPTS

Students should have previously studied the particulate nature of matter and the
concept of atoms as building blocks of matter.
 

RELATED SKILLS

Use of calculator for exponential numbers.

 
PERFORMANCE OBJECTIVES

After completing their study of atomic structure, students should be able to:
1. show the interrelationships of atomic number, atomic mass, numbers of
protons, neutrons, and electrons.
2. describe the relative energies of ultraviolet, visible, infrared, microwave, X-ray,
radio, and TV waves.
3. determine the electron configuration of a specified neutral atom.
4. draw an orbital diagram that correlates with a given electron configuration.
5. identify the maximum number of electrons that can occupy a shell or set of
orbitals.
6. distinguish between absorption (excitation) and emission of energy.
 

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