• Element
  • Atom
  • Protons
  • Nucleus
  • Electrons
  • Neutrons
  • Atomic number
  • Periodic table
  • Array
  • Atomic mass
  • Period
  • Group
  • Chemical properties
  • Physical properties
  • Molecule
  • Bond
  • Chemical bond
  • Valence electron
  • Ion
  • Ionic bond
  • Nonmetal
  • Metal
  • Covalent bond
  • Metallic bond
  • Conductivity


Students know:
  • Elements are substances composed of only one type of atom each having an identical number of protons in each nucleus.
  • Atoms are the basic units of matter and the defining structure of elements.
  • Atoms are made up of three particles: protons, neutrons and electrons.
  • The number of protons in an atom's nucleus is equal to the atomic number.
  • The periodic table arranges all the known elements in an informative array.
  • Elements are arranged left to right and top to bottom in order of increasing atomic number. Order generally coincides with increasing atomic mass.
  • Rows in the periodic table are called periods. As one moves from left to right in a given period, the chemical properties of the elements slowly change.
  • Columns in the periodic table are called groups. Elements in a given group in the periodic table share many similar chemical and physical properties.
  • The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state). The number of electrons in a period increases as one traverses down the periodic table; therefore, as the energy level of the atom increases, the number of energy sub-levels per energy level increases.
  • A molecule is formed when two or more atoms bond together chemically.
  • A chemical bond is the result of different behaviors of the outermost or valence electrons of atoms.
  • Ionic bonds are the result of an attraction between ions that have opposite charges. Ionic bonds usually form between metals and nonmetals; elements that participate in ionic bonds are often from opposite ends of the periodic table. One example of a molecule that contains an ionic bond is table salt, NaCl.
  • Covalent bonds form when electrons are shared between atoms rather than transferred from one atom to another. The two bonds in a molecule of carbon dioxide, CO2, are covalent bonds.
  • Metallic bonds exist only in metals, such as aluminum, gold, copper, and iron. In metals, each atom is bonded to several other metal atoms, and their electrons are free to move throughout the metal structure. This special situation is responsible for the unique properties of metals, such as their high conductivity.


Students are able to:
  • Analyze patterns within the periodic table to construct models of atomic and molecular structure, composition, and characteristics.
  • Identify the relevant components of the atomic and molecular models.
  • Describe relationships between components of the atomic and molecular models.


Students understand that:
  • Patterns in the periodic table predict characteristic properties of elements. These trends exist because of the similar atomic structure of the elements within their respective group families or periods, and because of the periodic nature of the elements.
  • The structure, composition, and characteristics of atoms and molecules are dependent upon their position in the periodic table.

Scientific and Engineering Practices

Developing and Using Models

Crosscutting Concepts