BONDING UNIT ATOMS, ELEMENTS, MOLECULES, COMPOUNDS AND MIXTURES NOTES

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

ATOMS –VS.- MOLECULES  Some elements exist as single atoms.  Smallest particle of an element that retains the properties of the element.  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. The substances retain their chemical properties. They are not chemically bonded.

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