Review Complete Questions 6, 7 and 9 on page 214

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1 Review Complete Questions 6, 7 and 9 on page 214 Title: Jan 5 8:43 AM (1 of 69)

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6 Title: Mar 6 7:50 PM (6 of 69) Section 5.11

7 Structure of Ionic Compounds Ionic compounds are formed when some atoms give up electrons, becoming positively charged, while others gain electrons, becoming negatively charged. The difference in positive and negative charges holds the atoms together. The formula for an ionic compound shows the ratio of atoms which make up the compound, called a formula unit. We often use the termolecule to describe a unit of a compound. However, formula units in ionic compounds are not true molecules. The positive and negative ions form a sort of matrix, with all of the cations held together with all of the anions. Title: Feb 12 6:47 PM (7 of 69)

8 Structure of Ionic Compounds In an ionic compound, all of the ions are held together. There is no individual, distinct particle which makes up the compound. Title: Feb 12 6:47 PM (8 of 69)

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13 Molecular Compounds In contrast, molecular compounds are formed when atoms share valence electrons. A shared pair of electrons forms covalent a bond. The number of unpaired valence electrons an atom has is called the combining capacity of the atom. It is the same as the number of electrons the atom would need to gain to fill its valence shell. When atoms share electrons, they form neutral particles called molecules. Each molecule is separate from other molecules, and individual molecules have little attraction between one another. This leads to one of the differences between ionic and molecular compounds: ionic compounds all have much higher melting and boiling points than molecular compounds. Title: Feb 12 6:47 PM (13 of 69)

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15 Structure of Molecular Compounds We will use a different type of atomic model, called Lewis a diagram, for drawing molecular compounds. To draw a Lewis diagram, follow two simple steps: *Write the symbol for the element *Use dots or "x"s to represent only the valence electrons, following the octet rule Octet Rule: An atom will have a number of unpaired electrons equal to the combining capacity of the element. Even for elements in periods 4 7, you can draw the valence electrons as if 8 is the maximum. Title: Feb 12 6:47 PM (15 of 69)

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19 Example: Draw the Lewis diagram to represent a Chlorine atom. Use Lewis diagrams to show how two chlorine atoms could form a molecule. Title: Mar 7 1:50 PM (19 of 69)

20 A molecule formed from two atoms of the same element is called a diatomic molecule. Several elements exist naturally as diatomic molecules: H, N, O, F, Cl, Br, I Notice that there are seven of these elements, and if you look at their location on the Periodic Table, they form the shape of a 7 at the right side of the table. (With hydrogen up in the corner.) This is why the symbols for these elements are always written as a molecule in a chemical equation. Ex: 2 H2 + O2 2 H2O Title: Jan 6 8:27 AM (20 of 69)

21 Multiple Covalent Bonds Atoms may form more than just single bonds. It is possible for atoms to form double or even triple covalent bonds. Example: Use Lewis diagrams to represent an Oxygen molecule. Title: Feb 12 6:47 PM (21 of 69)

22 Multiple Covalent Bonds Example: Use Lewis diagrams to represent an Nitrogen molecule. Title: Feb 12 6:47 PM (22 of 69)

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24 Multiple Covalent Bonds Example: Use Lewis diagrams to represent the molecule C2H6. How would you represent the molecule C2H2? Title: Feb 12 6:47 PM (24 of 69)

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27 Structure of Molecular Compounds Other properties which separate ionic and molecular compounds are also a result of their different structural elements: Ionic Compounds High melting and boiling points Most dissolve in water (polar solvent) Most are electrolytes Molecular Compounds Lower melting and boiling points Most are not water soluble (do not dissolve in water) Most are not electrolytes Title: Feb 12 6:47 PM (27 of 69)

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29 Structure of Molecular Compounds Why are molecular compounds composed entirely of nonmetals? Why can't metals form covalent bonds? Title: Feb 12 6:47 PM (29 of 69)

30 Naming Molecular Compounds When naming molecular compounds, you will use prefixes before each element to indicate how many of atoms of that element are in each molecule. This is because, unlike ionic compounds which always join elements in the same ratio, molecular compounds containing the same elements can be formed in many different ratios. Number Prefix 1 mono* 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca *Only use the prefix mono with oxygen, and then only if it is the final element in the molecule Title: Feb 12 6:47 PM (30 of 69)

31 Common Names In addition to the system names, many molecular compounds also have common names. For example, the molecule H2O could be named dihydrogen monoxide; however, nobody actually calls it that...it's just water". " Some other common names for molecules include: NH3 Ammonia CH4 Methane C3H8 Propane C4H10 Butane Compounds composed entirely of carbon and hydrogen are called hydrocarbons. These are a special class of organic compounds, and are very commonly used as fuels. Title: Feb 12 6:47 PM (31 of 69)

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41 Homework Complete Questions #4 6 on page 204 Title: Feb 12 6:47 PM (41 of 69)

42 Writing Formulas for Molecular Compounds Use Lewis diagrams to create models of molecular compounds. Write their formulas and/or their names. Title: Jan 7 8:31 AM (42 of 69)

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55 Writing Formulas for Molecular Compounds Use the diagrams to create models of molecular compounds. Write their formulas, and their names. C N O F Si P S Cl Se Br I Title: Feb 12 6:47 PM (55 of 69)

56 Writing Formulas for Molecular Compounds Use the diagrams to create models of molecular compounds. Write their formulas, and their names. C N O F Si P S Cl Se Br I Title: Feb 12 6:47 PM (56 of 69)

57 Writing Formulas for Molecular Compounds Use the diagrams to create models of molecular compounds. Write their formulas, and their names. C N O F Si P S Cl Se Br I Title: Feb 12 6:47 PM (57 of 69)

58 Writing Formulas for Molecular Compounds Use the diagrams to create models of molecular compounds. Write their formulas, and their names. C N O F Si P S Cl Se Br I Title: Feb 12 6:47 PM (58 of 69)

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60 H Polyatomic Ions Polyatomic ions are held together by covalent bonds. They are, in fact, molecular compounds which have an overall positive or negative charge. Because of this net charge, they will bond to other ions to form complex ionic compounds. Ex: Nitrate (NO31 ) Ammonium (NH41+) 1 O N O H N 1+ H H Title: Feb 12 6:47 PM (60 of 69)

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63 Polyatomic Ions Use Lewis diagrams to represent some polyatomic ions. Title: Feb 12 6:47 PM (63 of 69)

64 Homework Read Section 5.9 (pages ) and complete Questions #1 4 on page 198 Title: Feb 12 6:47 PM (64 of 69)

65 Common Names of Compounds Many common compounds have familiar "common" names which are almost always used instead of their system names. Some examples are: Water Ammonia Methane Title: Feb 12 6:47 PM (65 of 69)

66 Common Names of Compounds Other common compounds are: Butane Propane Glucose Title: Feb 12 6:47 PM (66 of 69)

67 Diatomic Molecules Several elements will form molecules by forming covalent bonds between two atoms of the same element. For example: Fluorine exists as F 2 Oxygen exists as O2 Title: Feb 12 6:47 PM (67 of 69)

68 Diatomic Molecules There are a total of seven elements which form diatomic compounds: N, O, F, Cl, Br, I, and H (When you look at these on the Periodic Table, you see that they form the shape of a 7, plus Hydrogen) Title: Feb 12 6:47 PM (68 of 69)

69 Writing Formulas for Molecular Compounds Use the diagrams to create models of molecular compounds. Write their formulas, and their names. C N O F Si P S Cl Se Br I Title: Feb 12 6:47 PM (69 of 69)