NSES Content Standard B  Physical Science: Structure and properties of matter Grades 9-12, page 178 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 "Periodic Table" is a consequence of the repeating pattern of outermost electrons and their permitted energies.

 
Benchmark 4D The Physical Setting: Structure of Matter
Grades 6-8, page 78
All matter is made up of atoms, which are far too small to see directly through a microscope. The atoms of any element are alike but are different from atoms of other elements. Atoms may stick together in well-defined molecules or may be packed together in large arrays. Different arrangements of atoms into groups compose all substances.

Benchmark 4D The Physical Setting: Structure of Matter
Grades 9-12, page 80
Atoms are made of a positive nucleus surrounded by negative electrons. An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons.

Benchmark 4D The Physical Setting: Structure of Matter
Grades 9-12, page 80
When elements are listed in order by the masses of their atoms, the same sequence of properties appears over and over again in the list.