Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Chemical Formulas for Molecules

Chemical Formulas and Chemical Bonds
Atoms interact with one another by transferring or sharing electrons that are farthest from the nucleus. These outer electrons govern the chemical properties of the element.

Bonds between atoms are created when electrons are paired up by being transferred or shared. A substance composed of a single kind of atom is called an element. The atoms may be bonded together into molecules or crystalline solids. A compound is formed when two or more kinds of atoms bind together chemically.

Further Description:

Classes of compounds formed from the transfer or sharing of outer electrons can be distinguished on the basis of solubility and electrical conductivity.

The position of elements in the periodic table and information about related trends in atomic properties can be used to predict the formulas and properties of compounds. Formulas of compounds also can be deduced from quantitative information such as percent composition and molar mass.

Lewis dot diagrams can be written to show how outermost electrons in the constituent atoms are distributed.

Concepts Needed:

Grade 9

Solubility, electrical conductivity, atomic symbols

Grade 10

Electron transfer, electron sharing, ionic bonds, covalent bonds, Lewis dot diagram, valence electrons, cations, anions

Grade 11

Molecular formula, empirical formula, percent composition

Grade 12

Bond energy, electronegativity, bond strength

Empirical Laws or Observed Relationships:

The periodic law

Theories or Models:

Lewis electron-pair bond model, the chemical bond theory

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Micro-Unit Description:

Chemical Formulas for Molecules
Students should be able to interpret chemical formulas in terms of the kinds and numbers of particles (atoms) they contain. They should also be able to use ball and stick models to model a variety of structures produced by particles bonding with each other

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