Covalent Bonding Unit 2 Chemistry 11 Mrs. Purba

Homework Solutions

Covalent Bonding: Involves the “ sharing ” of electrons. Involves the “ sharing ” of electrons. It involves the bonds formed between a non- metal and a non-metal (or metalloid). It involves the bonds formed between a non- metal and a non-metal (or metalloid).

Important: Since these bonding non-metals (or metalloids) wish to gain electrons to become like a noble gas, and they can’t gain electrons from each other at the same time, they must share their electrons so they can both become like a noble gas. Since these bonding non-metals (or metalloids) wish to gain electrons to become like a noble gas, and they can’t gain electrons from each other at the same time, they must share their electrons so they can both become like a noble gas. These compounds or molecules that are formed are neutral …they have no charge. These compounds or molecules that are formed are neutral …they have no charge.

Examples 1.H 2 O (water) 2.CO 2 (carbon dioxide) 3.O 2 (oxygen)

Nomenclature: Different classes of compounds have different rules for naming. Different classes of compounds have different rules for naming. Before naming a compound, it is important to check which class it belongs to so that you will use the appropriate set of rules. Before naming a compound, it is important to check which class it belongs to so that you will use the appropriate set of rules.

Rules for Naming Binary Molecular Compounds To use this set of rules, the compound must be a molecular or covalent compound. To use this set of rules, the compound must be a molecular or covalent compound. In other words, it must be a non-metal + a non-metal (or metalloid) compound In other words, it must be a non-metal + a non-metal (or metalloid) compound

Rules: Name the first element as the name you see on your periodic table. Name the first element as the name you see on your periodic table. Name the second element as you see it in your “Periodic Table of Ions”…the 2nd element always ends in “- ide ” Name the second element as you see it in your “Periodic Table of Ions”…the 2nd element always ends in “- ide ” Use numerical prefixes to show how many of each atom is present in the molecule. Use numerical prefixes to show how many of each atom is present in the molecule. Mono- is frequently or often, omitted for the first element. Mono- is frequently or often, omitted for the first element. Write these on the “file cards” then place them in your plastic sheath. Write these on the “file cards” then place them in your plastic sheath.

Prefix Number of Atoms in Compound Mono-1 Di-2 Tri-3 Tetra-4 Penta-5 Hexa-6 Hepta-7 Octa-8 Nona-9 Deca-10

Naming Binary Molecular Compounds Write the names of the following covalent compounds : 1.SO 3 _______________________________________ 2.N 2 S _______________________________________ 3.PH 3 _______________________________________ 4.BF 3 _______________________________________ 5.P 2 Br 4 ______________________________________ 6.CO ________________________________________ 7.SiO 2 _______________________________________ 8.SF 6 _______________________________________ 9.NH 3 _______________________________________ 10.NO 2 ________________________________________ Sulphur trioxide Diphosphorous tetrabromide Carbon monoxide silicon dioxide Sulphur hexafluoride Nitrogen trihydride or Ammonia nitrogen dioxide Dinitrogen monosulfide Phosphorous trihydride Boron trifluoride

Formula Writing of Binary Molecular Compounds 1.nitrogen trichloride ________________________ 2.boron monocarbide __________________________ 3.dinitrogen trioxide ________________________ 4.phosphorus pentafluoride __________________ 5.methane ______________________________ 6.sulfur dibromide _________________________ 7.diboron tetrahydride ______________________ 8.oxygen difluoride _________________________ 9.carbon disulfide __________________________ NCl 3 CS 2 N2O3N2O3 PF 5 CH 4 SBr 2 B2H4B2H4 OF 2 BC

A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. Why should two atoms share electrons? FF + 7e - FF 8e - F F F F Lewis structure of F 2 lone pairs single covalent bond

8e - H H O ++ O HH O HHor 2e - Lewis structure of water Double bond – two atoms share two pairs of electrons single covalent bonds O C O or O C O 8e - double bonds Triple bond – two atoms share three pairs of electrons N N 8e - N N triple bond or 9.4

Lengths of Covalent Bonds Bond Lengths Triple bond < Double Bond < Single Bond

H F F H Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms electron rich region electron poor region e - riche - poor ++ -- 9.5

Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond. Electronegativity – Linus Pauling Scale, F is highest

The Electronegativities of Common Elements

Classify the following bonds as ionic, polar covalent, or non-polar covalent… the bond in CsCl; the bond in H 2 S; and the NN bond in H 2 NNH 2. Cs – 0.7Cl – – 0.7 = 2.3Ionic H – 2.1 S – – 2.1 = 0.4 Polar Covalent N – – 3.0 = 0 Non-polar

Non-Polar Covalent share e- Polar Covalent partial transfer of e - Ionic transfer e - Increasing difference in electronegativity Classification of bonds by difference in electronegativity DifferenceBond Type 0Non-polar Covalent  1.7 Ionic 0 < and < 1.7 Polar Covalent 9.5