Covalent Bonds and Molecular Geometry

1. Covalent Bonds and Molecular Geometry Name and Formulas Binary Molecular Compounds Acids Lewis Symbols and Lewis Structures Geometries: Electron Domain Molecular Polarity

2. Compounds • Compounds form when the valence electrons present in the atoms of two or more different elements interact. • If electrons are transferred from one element to another, ions are formed, and an ionic compound results. • If electrons are shared between two or more atoms, then a covalent bond forms, and a molecular compound results.

3. Compounds • Ionic compounds are composed of ions that are held together by ionic bonds. • Electrostatic force of attraction between oppositely charged particles. • Ionic compounds often contain a metal and one or more nonmetals. • NaCl • Al2(CO3)3 • Compounds containing the ammonium ion are also ionic! • (NH4)2SO4

4. Molecular Compounds • Molecular compounds are composed of atoms that are held together by covalent bonds. • The attractive force between two atoms that results from sharing electrons • Each pair of shared electrons is represented by a single straight line. • Molecular compounds usually contain non-metals only.

5. Naming Binary Molecular Compounds • Binary molecular compounds are composed of molecules containing two non-metals that share electrons. • The names of binary molecular compounds give both the number and type of each atom present. Prefix element name prefix element name with “ide” ending • Greek prefixes are used to indicate the number of each atom present in a molecule of the compound.

6. Naming Binary Molecular Compounds • You must know the prefixes for one through ten. P4S10 Tetraphosphorus decasulfide Prefix Meaning mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 nona 9 deca 10

7. Naming Binary Molecular Compounds • Special conventions for using Greek prefixes: • Mono is never used with the first element (but it’s always used if only one atom of the second element is present) • The ending “a” or “o” in a prefix is dropped if the name of the element begins with a vowel. • CO: • Not monocarbon monooxide • carbon monoxide

8. Naming Binary Molecular Compounds Example: Name the following binary molecular compounds. N2O4 PCl5 Cl2O7 SO3

9. Formulas for Binary Molecular Compounds • To write the formula for a binary molecular compound: • Write the elemental symbol of the first atom listed in the name. • Use the numerical value of the prefix in front of that element as the subscript. • Write the elemental symbol for the second element present. • Use the prefix in front of the “ide” element as the subscript for the second element. Diphosphorus pentoxide P2O5

10. Formulas for Binary Molecular Compounds Example: Write the correct formula for each of the following compounds. Dinitrogen monoxide Phosphorus pentachloride Xenon hexafluoride Disulfur dichloride

11. Acids • Acids are molecular compounds that form hydrogen ions (H+) when dissolved in water. • HCl (aq) • H2S (g) • H3PO4 (aq) • Acids can be recognized because: • Their formula starts withHn or • Their formula containsCOOH, CO2Hor

12. Naming Acids • The name of an acid depends on the type of acid: • Acids with oxygen (oxyacids) • Acids without oxygen • Gases (pure) • Aqueous solutions (dissolved in water)

13. Oxyacids • Oxyacids are acids that contain oxygen. • If the acid contains oxygen, • Write the name of the anion • Change anion ending from “ate” to “ic acid” OR • Change anion ending from “ite” to “ous acid” HNO3 nitrate nitricacid HNO2 nitrite  nitrous acid

14. Oxyacids • Naming acids derived from oxyanions of S or P: • H2SO4 : • oxyanion = sulfate • Sulfic acid Sulfuric acid • H3PO4 : • oxyanion = phosphate • Phosphic acid Phosphoric acid

15. Acids w/o Oxygen – Pure (Gases) • If the acid does not contain oxygen and is a gas (g): • Name the acid as if it was an ionic compound: • Start with “hydrogen” • Do not use a prefix to indicate how many hydrogen atoms are present! • Add the name of the anion H2S (g) hydrogen sulfide HBr (g) hydrogen bromide

16. Acids w/o Oxygen – Dissolved in H2O • If the acid does not contain oxygen and is dissolved in water (aq): • Start with hydro • Add the name of the anion • Change “ide” to “ic acid” HBr (aq) hydrobromic acid HI (aq) hydroiodic acid

17. Naming Acids Example: Write the correct name for the following acids. HCl (aq) HC2H3O2 HCN (g)

18. Formulas for Acids • Given the name of an acid, you should be able to write its formula: • First decide which category of acid it is: • No oxygen, (aq) (begins with “hydro”) • No oxygen, (g) (begins with “hydrogen”) • Oxyacid • Write the formula for the anion (including charge). • Add enough H+ ions to make a neutral compound. • Add (g) or (aq) if appropriate.

19. Formulas for Acids Example: Write the formula for: Carbonic acid Hydrogen sulfide Acetic acid Hydrochloric acid

20. Naming Acids • You must know the names and formulas for the following acids: HF (aq) hydrofluoric acid HCl (aq) hydrochloric acid HBr (aq) hydrobromic acid HI (aq) hydroiodic acid HClO4 perchloric acid HClO3 chloric acid H2SO4 sulfuric acid HNO3 nitric acid

21. Naming Acids • You must know the names and formulas for the following acids: H3PO4 phosphoric acid HC2H3O2 acetic acid H2CO3 carbonic acid H2S (g) hydrogen sulfide HCN (g) hydrogen cyanide HF (g) hydrogen fluoride HCl (g) hydrogen chloride HBr (g) hydrogen bromide HI (g) hydrogen iodide

22. Naming - Revisited Example: Write the correct formula for each of the following. Calcium nitrate Dinitrogen trioxide Phosphoric acid Aluminum hydroxide Hydrogen sulfide

23. Naming – Revisited • Before you can correctly name a compound or write its formula, YOU MUSTdetermine which type of compound it is: • Ionic starts with a metal or NH4 • Acid starts with H or Hn • Binary Molecular two non-metals • THEN use the appropriate naming system or method to write the formula.