Formation of Compounds Answers to the notes outline will be highlighted in blue.

 The chemical name tells you what elements make up the compound: sodium and chlorine.  Where is it found? ◦ It is found in large, solid, underground deposits and dissolved in the ocean.  How is it used? ◦ To enhance food flavor ◦ To melt ice on roadways.

 What are some physical properties of NaCl? ◦ White crystalline, solid at room temperature ◦ It is brittle ◦ melts at 800°C ◦ It dissolves easily in water ◦ Only conducts electricity in aqueous form (dissolved in water) or when melted. ‣ What are some chemical properties of NaCl? o It does not react readily with other substances (it is stable or unreactive)

Properties of Salt How do the properties of salt compare with the properties of its component elements, sodium and chlorine?  Properties of Sodium ◦ Shiny, silvery-white, soft, metallic solid ◦ Melts at 98°C ◦ Stored in oil because it reacts with oxygen and water vapor in air ◦ One of the most reactive of the common elements ◦ Always found combined with other elements  Properties of Chlorine ◦ Non-metallic pale green, poisonous gas ◦ Kills living cells ◦ slightly soluble in water ◦ Used as a disinfectant ◦ Condenses into a liquid at -34°C ◦ One of the most reactive elements ◦ Has industrial importance Reaction of Sodium and Chlorine

 The chemical name tells you what elements make up the compound: Carbon and two oxygen atoms.  Where is it found? ◦ In the atmosphere ◦ In your bloodstream as a waste product of cellular respiration.  How is it used ? ◦ It is used by plants to make glucose (photosynthesis)

 What are the physical properties of CO 2 ? ◦ It is a colorless, odorless, and tasteless gas. ◦ Below -80°C, the gas changes directly to white solid without first becoming a liquid (dry ice). ◦ It is soluble in water, but a weak conductor of electricity.  What are the chemical properties of CO 2 ? ◦ It is relatively stable. ◦ It is used in fire extinguishers because it does not support burning. ◦ It is involved in photosynthesis.

 Properties of Oxygen ◦ Nonmetallic, colorless, odorless, and tasteless gas ◦ Oxygen supports burning ◦ Becomes a liquid when cooled to -183°C ◦ Slightly soluble in water ◦ More reactive than carbon and combines with many other elements ◦ Most abundant element in the Earth’s crust  Properties of Carbon ◦ Nonmetallic and unreactive at room temperature ◦ Reacts with other elements at high temperatures ◦ Carbon burns easily and is a good source of heat ◦ Form a huge variety of compounds (organic chemistry) Properties of Carbon Dioxide

 The chemical name tells you what elements make up the compound: two hydrogen atoms and one oxygen atom  Where is it found? ◦ It is approximately 70% of Earth’s surface ◦ It is about 70% of the mass of the average human body.  How is it used? ◦ In chemistry water dissolves chemicals so that can interact with other chemicals to create chemical reactions.

 What are the physical properties of water? ◦ It is the only 1 of the 3 compounds that occurs in Earth’s environment in all 3 states of matter. ◦ It turns into a gas at 100°C and turns into a solid at 0°C. ◦ Pure water does not conduct electricity as a solid, liquid, or a gas. ◦ It is called the universal solvent because it is good at dissolving other substances. ◦ It is important in transport of materials.

 What are the chemical properties of water? ◦ Water is a stable compound that doesn’t break down under normal conditions and doesn’t react with many other substances. ◦ It acts as a medium for chemical reactions to occur. ◦ It is important during photosynthesis

Properties of Water  Properties of Hydrogen ◦ Lightest and most abundant element in the universe ◦ Nonmetallic, odorless, tasteless, and colorless gas ◦ Reactive element, so rarely found as a free element ◦ Turns into a liquid at -253°C ◦ Does not conduct electricity ◦ Slightly soluble in water  Properties of Oxygen ◦ Refer back to slide 10 Combustion of hydrogen and oxygen

 Can you make any conclusions about compounds and the elements that make them up? ◦ The physical and chemical properties of the atoms that make up compounds are very different from the compounds they create.

 For elements to react, atoms of the elements must collide.  It is the valence electrons of colliding atoms that interact to form compounds. ◦ Remember from chapter 3 that the properties of elements repeat because the number of valence electrons repeat in each group. ◦ The number of valence electrons determines the chemical properties of an atom.

 Why are noble gases so unreactive and so stable? ◦ Each noble gas (except for Helium) has 8 valence electrons  The octet rule states that atoms can become stable by having 8 electrons in their outer energy level. ◦ Elements become more stable by achieving a noble gas configuration. ◦ They do this by gaining, losing or sharing electrons with other elements.

 How many valence electrons do sodium and chlorine have? ◦ Sodium has 1 and chlorine has 7  How can both sodium and chlorine achieve a full octet? ◦ The 1 valence electron of sodium is transferred to the chlorine atom. Na + Cl[ Na ] + [ Cl ]NaCl + -

 When sodium transfers its one valence electron to chlorine both atoms become charged particles called ions. ◦ Metals (like sodium) lose electrons and become positively charged particles called cations. ◦ Non-metals (like chlorine) gain electrons and become negatively charged particles calledanions. ◦ The strong attractive force between ions of opposite charge creates an ionic bond.  A compound that is composed of ions is called an ionic compound.

Structure  Every + sodium atom attracts every – chlorine atom and vice versa. ◦ The ions organize themselves into a definite cube-shaped arrangement called a crystal. ◦ A crystal is a regular, repeating arrangement of atoms, ions, or molecules. Formula The formula of a compound tells what elements make up the compound and how many atoms of each element are present in one unit of the compound. Sodium chloride = NaCl 1 sodium atom and 1 chlorine atom make up one unit of sodium chloride

 When atoms collide with enough energy to react, but neither attracts electrons strongly enough to take electrons from the other atom, the atoms combine by sharing valence electrons. ◦ Electrons can only be shared to form molecules when 2 nonmetals collide. ◦ NOTE: Compounds cannot be formed from two metals!!!!!!

 The attraction of 2 atoms for a shared pair of electrons is called a covalent bond.  A compound whose atoms are held together by covalent bonds is a covalent compound (also called molecular compounds).  A molecule is an uncharged group of 2 or more non- metal atoms held together by covalent bonds.  Single, double and triple covalent bonds are possible when 1, 2 or 3 pairs of electrons are shared.

Ionic vs. Covalent  Ionic Compounds ◦ Well-organized, tightly bound e - ◦ Form crystals ◦ Hard, rough, and brittle ◦ High melting point ◦ Soluble in water ◦ Conduct electricity when dissolved in water ◦ Any compound that conducts electricity when melted or dissolved in water is an electrolyte.  Covalent Compounds ◦ Attractive forces between molecules are weak ◦ The forces between particles that make up a substance are called interparticle forces. ◦ Liquids or gases at room temperature ◦ Do not conduct electricity ◦ Do not dissolve in water