Analysis question 1 Make a copy of the table below in your science notebook. Use the Periodic Table of Elements to find out which atoms make up a molecule for each of the substances listed. The first row has been completed for you.

Analysis question 2 Sodium is a metallic solid, and chlorine is a poisonous yellow-green gas. Sodium and chlorine react to form sodium chloride, which is common table salt. a. Is table salt an element or a compound? Explain. b. Describe the physical properties of table salt. c. How do the properties of table salt compare with those of sodium and chlorine?

Analysis question 3 Is seawater an element, compound, or mixture? Explain your answer.

Analysis question 4 Explain the relationship between an atom and a molecule.

What are elements, and how do they relate to compounds?

Key vocabulary definitions Atom - The basic structural unit of an element. Atomic mass - The average mass of atoms of an element; also known as atomic weight.

Key vocabulary definitions Chemical formula - A shorthand notation to describe elements and compounds and their reactions. Each element is identified by one or two letters. For example, H represents hydrogen, Cl represents chlorine, and O represents oxygen. A compound is identified by its combination and proportion of elements. For example, H2O represents water. Reactions are represented as equations with an arrow indicating direction of change instead of an equals sign. For example, the reaction between hydrochloric acid and sodium hydroxide to produce water and sodium chloride is represented by HCl + NaOH ⇛ H2O + NaCl.

Key vocabulary definitions Compound - A homogeneous, pure substance composed of two or more essentially different elements that are chemically combined and that are thus present in definite proportions. For example, H2O contains two atoms of hydrogen and one atom of oxygen chemically combined to produce a new substance with properties quite different from either hydrogen or oxygen.

Key vocabulary definitions Element - A substance that cannot be broken down into simpler substances by chemical or physical means. Family - Elements with similar chemical properties arranged in the same column of the periodic table.

Key vocabulary definitions Molecule - The smallest particle of an element or compound that displays the properties of the substance in quantity.

For links to learn more about Dmitri Mendeleev’s work and the work of other chemists, visit the SEPUP website: www.sepuplhs.org