BONDING UNIT LEARNING GOAL #2: EXPLAIN THAT THE PROPERTIES OF A COMPOUND MAY BE DIFFERENT FROM THOSE OF THE ELEMENTS OR COMPOUNDS FROM WHICH IS FORMED.

ELEMENTS Pure substances that contain only one kind of atom. Examples: Hydrogen, Copper, Iron

ATOMS –VS.- MOLECULES  Some elements exist as single atoms.  Other elements exist as molecules.  Molecules consist of 2 or more atoms combined in a definite ratio.

COMPOUNDS  A substance made up of atoms of two or more different elements joined by chemical bonds.

WHAT IS THE DIFFERENCE BETWEEN A COMPOUND AND A MOLECULE?  A molecule is formed when two or more atoms join together chemically.  A compound is a molecule that contains at least two different elements.  All compounds are molecules but not all molecules are compounds.

Mixture: A sample of matter that contains two or more pure substances (elements and compounds) and has variable composition.

Exhaust –a Mixture

MIXTURES AND COMPOUNDS DIFFER IN TWO WAYS… Substances in a mixture keep their individual properties. Parts of a mixture are not necessarily present in specific ratios.

SOLUTIONS  Homogeneous mixture : is a substance in which two or more substances are uniformly spread out.  Example: salt water, stainless steel, maple syrup  Solution is another term for homogeneous mixture.  Heterogeneous Mixture : A mixture contains substances that are not evenly mixed.  Example: Orange juice, granite, sand

Salt= NaCl Properties of Salt: White solid at room temperature. The crystals are brittle. Melting Point 800 o C Conducts electricity when melted or in aqueous solutions. Soluble in water. Unreactive Safe to store for long periods of time. Used to season food. Safe to eat. Properties of Sodium: Shiny, silvery-white, soft, solid element. Metallic Element Melting Point of 98 o C Boiling Point of 883 o C Most reactive of all the common elements. Has to be stored under oil. Never found as a free element in the environment. Always found combined with other elements Properties of Chlorine: Pale green, poisonous gas with a choking odor. Kills living cells. Slightly soluble Gas until -34 o C then turns into a liquid Very Reactive

Carbon Dioxide = CO 2 Properties of Carbon: Nonmetal Fairly unreactive at room temperature. Reacts with many elements at higher temperatures. Majority of compounds in living organisms have carbon in them. Solid at room temperature. Melting Point 3,527 o C Boiling Point 4,027 o C Properties of Oxygen: Nonmetal Colorless, odorless, and tasteless gas Oxygen reacts during combustion reactions. Turns into a liquid when cooled to -183 o C. Properties of Carbon Dioxide: Colorless, odorless, and tasteless gas. Changes directly to a solid at -80 o C Soluble in water Relatively stable Extinguishes Fire Burning carbon compounds in air will make carbon dioxide.

Water = H 2 O Properties of Hydrogen: Lightest most abundant element in the universe. Nonmetal Odorless, tasteless, and colorless gas Very Reactive Seldom found as a free element Must be cooled to -253 o C to turn to a liquid. Does not conduct electricity Slightly soluble. Properties of Oxygen: Nonmetal Colorless, odorless, and tasteless gas Oxygen reacts during combustion reactions. Turns into a liquid when cooled to -183 o C. Properties of Water: Occurs on earth in all 3 states of matter Does not conduct electricity in any of the states Universal Solvent Stable Compound Acts as a medium for chemical reactions

ESSENTIAL QUESTIONS 1.How is a chemical formula used to identify the number and kinds of elements in a compound? 2.How can a formula define a specific compound? 3.Use data to compare the physical properties of a compound to the properties of the elements that comprise it. 4.Use data to compare the chemical properties of a compound to the properties of the elements that comprise it. 5.Must a specific compound necessitate one unique chemical formula?