Chapter 4 Formation of Compounds 4.1 The Variety of Compounds 4.2 How Elements Form Compounds

4.1 The Variety of Compounds

Objectives Distinguish the properties of compounds from those of elements of which they are composed. Compare and contrast the properties of sodium chloride, water and carbon dioxide. Analyze evidence to conclude the differences exist in the ways compounds form.

Salt: A Familiar Compound Chemical Name: Sodium Chloride Formula: NaCl Very abundant in nature Large, solid, underground deposits Dissolved in the oceans Salt can be obtained by mining the solid deposits or evaporating the seawater

Sodium Chloride Uses Food enhancer Essential nutrient in living things Used to melt ice

Physical Properties of NaCl White solid at room temperature Crystalline Brittle Melting point: 800°C Dissolves easily in water Salt water is an excellent conductor of electricity

Chemical Properties of NaCl Does not react readily with other substances. Does not degrade quickly No special handling procedures

Properties of Sodium Shiny Silvery-white Soft Solid metal Melting point: 98°C Stored under oil b/c it reacts with oxygen and water vapor in the air

Properties of Sodium One of the most reactive of the common elements Free element sodium is never found in the environment Always combined with another element

Properties of Chlorine Pale green Poisonous gas Choking odor Kills living cells Slightly soluble in water Excellent disinfectant for water supplies and pools

Properties of Chlorine Nonmetal, halogen Gas must be cooled to -34°C before it turns to a liquid Among the most reactive of elements Handled with extreme care

Salt Formation

Formation of Sodium Chloride Two extremely reactive and unstable elements combine to form a stable, safe substance. + 

Review What are two physical properties of Sodium Chloride? What is a chemical property of Sodium Chloride? What are two physical properties of Sodium? What are two physical properties of Chlorine?

4.1 The Variety of Compounds (Continued)

Carbon Dioxide: A Gas to Exhale Formula: CO2 Colorless gas We exhale carbon dioxide as a result of respiration Plants use carbon dioxide and release oxygen during photosynthesis

Physical Properties of CO2 Colorless Odorless Tasteless Gas When cooled to -80°C, the gas changes directly to a white solid

Physical Properties of CO2 Soluble in water Weak conductor of electricity “Dry Ice”-does not melt to a liquid

Chemical Properties of CO2 Relatively stable Used in fire extinguishers-does not support burning Photosynthesis-most significant chemical reaction using CO2.

The Properties of Carbon Nonmetal Black, brittle solid Fairly unreactive at room temperature At higher temps will react with many elements Burns well: Charcoal is 90% carbon Forms a huge variety of compounds Organic chemistry?

The Properties of Oxygen Nonmetal Colorless Odorless Tasteless Gas 21% of the air we breathe Oxygen supports burning

The Properties of Oxygen Becomes a liquid when cooled to -183°C Slightly soluble in water More reactive than carbon Rusting Combines with many elements Most abundant element in Earth’s crust

Earth’s Crust

Water, Water Everywhere Formal Chemical name: Dihydrogen monoxide Formula: H2O Covers 70% of the Earth Approx. 70% of the mass of the average human body

Physical Properties of Water Three states: Solid, Liquid, Gas Boiling Point: 100°C Freezing Point: 0°C Pure water does not conduct electricity Excellent solvent “universal solvent” Vital in the transport of dissolved materials

Water

Chemical Properties of Water Stable Does not react with many other substances Medium in which many chemical reactions occur (human body) Starting material for photosynthesis

Properties of Hydrogen Lightest element Most abundant element in the universe Nonmetal Reactive element Odorless Colorless tasteless

Properties of Hydrogen Seldom found as a free element React vigorously with many elements, including oxygen forming water Becomes a liquid at -253°C Does not conduct electricity Only slightly soluble in water

Using Clues to Make a Case Elements combine to form compounds with different properties Elements do not always combine in the same way or all compounds would have similar properties We will examine how elements combine in the Section 4.2

Review What are some properties of Carbon Dioxide? What are some properties of Oxygen? What are some properties of Water? What are some properties of Hydrogen?