Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 5. (17)-Chemical Bonds Today’s Outline..Review of covalent bond..Rules for writing electron-dot formulas..Odd-electron molecules: Free radicals

Chapter 5. (L17)-Chemical Bonds Building Your Chemical Vocabulary Sulfuric acid: H 2 SO 4, a strong acid Sodium hydroxide: NaOH, a strong base Lead: Pb

Chapter 5. (L17)-Chemical Bonds Covalent bond: Shared electron pair(s), equal share, nonpolar..Non-polar covalent bond occurs to the molecules of the identical atoms: H· + ·H = H:H = H 2 one pair.... :O: + :O: = :O::O: = O 2 two pair :Cl· + ·Cl = :Cl:Cl: = Cl 2 one pair Again, only valence electron configuration is needed.

Chapter 5. (L17)-Chemical Bonds Covalent bond: Shared electron pair(s), unequal share, polar.. Polar covalent bond occurs to the molecules of atoms of somewhat different kinds (not strongly different), usually non-metals.... H· + ·Cl: = H:Cl:one pair.... H 2 + Cl 2 = 2HCl..Unequal sharing: Cl atom has more attraction to the electrons than H atom, more electronegative Cl atom would have a bit more negative charge, while H atom would have a bit more positive charge

Chapter 5. (L17)-Chemical Bonds Polyatomic covalent compounds and molecules.. Water, H:O:H8 – 6 = 2 bonds.. Ammonia, H:N:H8 – 5 = 3 bonds.. H Methane, H8 – 4 = 4 bonds.. H:C:H.. H

Chapter 5. (L17)-Chemical Bonds Names of covalent compounds and molecules..Common names from everyday life water, ammonia, methane..Use of prefix N 2 O 4, dinitrogen tetraoxide NO 2, nitrogen dioxide NO, nitrogen oxide CO, carbon monooxide CO 2, carbon dioxide SCl 2, sulfur dichloride SF 6, sulfur hexafluoride P 2 O 5, diphosphorous pentoxide CrO 3, chromium trioxide

Chapter 5. (L17)-Chemical Bonds Polyatomic ions hydroxide.... e - + ·O· + ·H = [:O:H] Table 5.4 on pp.135 of the textbook for more common polyatomic ions, both cations and anions

Chapter 5. (L17)-Chemical Bonds Rules for writing electron-dot formulas Ionic bond: e - transfer covalent bond: shared e - Both ionic bond and covalent bond: To achieve the octet electron configuration

Chapter 5. (L17)-Chemical Bonds Rules for writing electron-dot formulas A simple scheme: 1. Inspect the molecular formula 2. Determine the skeletal structure 3. Apply the bonds for each atom 4. Check to see if the octet electron configuration is achieved for each atom Tip: Experience and knowledge

Chapter 5. (L17)-Chemical Bonds Rules for writing electron-dot formulas Common patterns of the bonds for various atoms: H·, or H– :F: :Cl: :Br: :I: ·O·, or –O–......F– Cl– Br– I–. |.... ·C·, or –C– ·N·, or –N– ·P·, or –P –. |. |. | Note: – represents a pair of shared electrons See textbook Fig. 5.8 and Table 5.5 for a list.

Chapter 5. (L17)-Chemical Bonds Writing electron-dot formulas: Examples H 2, H–H; Cl 2, Cl–Cl; F 2, F–F; Br 2, Br–Br; I 2, I–I HCl, H–Cl; HF: H–F; HBr: H–Br; HI: H–I CO, :C O:.... CO 2, :O=C=O:.. NH 3, H–N –H | H

Chapter 5. (L17)-Chemical Bonds Writing electron-dot formulas: Examples H 2 O, H–O: O 2, :O=O: | H | CH 4, H –C –H | H

Chapter 5. (L17)-Chemical Bonds Odd-electron molecules: Free radicals Molecules with odd number of total electrons can never fit the octet configuration...The odd electron is always in the valence shell, because other inner shells are filled with paired electrons (always even numbers). Free radicals: Atoms and molecules with unpaired electrons..Because free radicals do not have the octet configuration, many of them are not stable, and highly reactive, with only transitory existence as intermediates in chemical reactions.

Chapter 5. (L17)-Chemical Bonds Some examples of free radicals... NO, :N::O:, nitrogen monoxide..... NO 2, :O:N::O:, nitrogen dioxide ClO 2, :O:Cl:O:, chlorine dioxide......

Chapter 5. (L17)-Chemical Bonds Quiz Time The electron-dot formula for CH 4 is (a) H 2 —C—H 2 ; (b) H—C—H 3 ; (c) H | H—C—H; | H (d) H—C—H.

Chapter 5. (L17)-Chemical Bonds Quiz Time The electron-dot formula for H 2 O is (a) H 2 —O—H 2 ; (b) O—H 2 ; (c).. :O—H; | H (d) O—H.

Chapter 5. (L17)-Chemical Bonds Quiz Time The electron-dot formula for CO 2 is (a) O 2 —C—O 2 ; (b) O—C—O; (c).... :O=C=O:; (d) O—O—C.

Chapter 5. (L17)-Chemical Bonds Quiz Time The number of bonds for N is usually (a) —N— ; (b) —N ; (c) —N— ; | (d) none of above.

Chapter 5. (L17)-Chemical Bonds Quiz Time The number of bonds for O is usually (a) —O— ; (b) —O ; (c) —O ; | (d) none of above.

Chapter 5. (L17)-Chemical Bonds Quiz Time The number of bonds for F is usually (a) —F— ; (b) —F ; (c) —F ; | (d) none of above.

Chapter 5. (L17)-Chemical Bonds Quiz Time The number of bonds for C is usually (a) —C—; (b) —C; (c) —C—; | (d) —C —. |

Chapter 5. (L17)-Chemical Bonds Quiz Time Which of the following molecules is a free radical? Is it (a) CO; (b) CO 2 ; (c) NO; (d) HCl.

Chapter 5. (L17)-Chemical Bonds Quiz Time Which of the following molecules is a free radical? Is it (a) O 2 ; (b) NO 2 ; (c) Cl 2 ; (d) HF.