3. Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. As a basis for understanding this concept:
- a. Students know the structure of the atom and know it is composed of protons, neutrons, and electrons.
- b. Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements.
- c. Students know atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long-chain polymers.
- d. Students know the states of matter (solid, liquid, gas) depend on molecular motion.
- e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently.
- f. Students know how to use the periodic table to identify elements in simple compounds.