Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Periodicity of the Elements

Elements, Atoms, and the Periodic Table
An element is composed of a single type of atom. When elements are listed in order according to the number of protons (called the atomic number), repeating patterns of physical and chemical properties identify families of elements with similar properties. This APeriodic Table@ is a consequence of the repeating pattern of outermost electrons and their permitted energies.


Further Description:

Elements can be grouped or classified according to their physical and chemical characteristics (metals, nonmetals, and metalloids). Early chemists grouped elements with very similar properties into families. These families could be arranged into a pattern called the periodic table. Each element is composed of a single type of atom containing a specific number of protons and an equal number of electrons.

When elements are listed in ascending order of the number of protons, the periodic table is seen to be a consequence of a repeating pattern of outermost electrons. Other atomic properties also follow patterns, including atomic size, ionic size, ionization energies, electron affinity, and electronegativity. Detailed electron configurations of atoms are also reflected in the periodic table and explain variations between closely related elements.


Concepts Needed:

Grade 9

Chemical family, periodic table, metal, nonmetal, metalloid

Grade 10

Valence electron, proton, neutron, atomic number, atomic mass number, isotope

Grade 11

Atomic size, ionic size, ionization energy, electronegativity, electrode potential, isotope, periodicity

Grade 12

Energy level, sublevel, orbital electron spin, electron affinity, electron configuration


Empirical Laws or Observed Relationships:

The periodic law


Theories or Models:

Atomic theory


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Micro-Unit Description:

Periodicity of the Elements
Students should understand that when elements are listed in ascending order of the number of protons (atomic number), the periodic table is seen to be a consequence of a repeating pattern of the elements' outermost electrons (valence electrons).


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