Chapter 9 Covalent Bonding Review Noble gases are

Chapter 9: Covalent Bonding

Review • Noble gases are the most stable – Have full outer energy level – Do not react with other elements to form bond • Metals and Nonmetals react – form binary ionic compounds – electrons are transferred – attain a noble gas configuration

• Sometimes two atoms that BOTH need to gain electrons to become stable will have a similar attraction for electrons • These atoms SHARE electrons • RECALL: Octet rule states that atoms will gain, lose, or share electrons in order to become stable

What is a covalent bond? • Covalent bond- results from the sharing of valence electrons • The shared electrons are considered to be part of the complete outer energy level • Forms between two non-metals

Molecules • Forms when two or more atoms bond covalently Ex. Carbohydrates, proteins, DNA, and fats

Formation of a Covalent Bond • Hydrogen (H 2), Nitrogen (N 2), Oxygen (O 2), Fluorine (F 2), Chlorine (Cl 2), Bromine (Br 2), and Iodine (I 2) are all diatomic molecules • Diatomic molecules form because they are more stable than the individual atoms • Consider two individual atoms of Fluorine. . .

• Fluorine’s electron configuration is as follows: 1 s 22 p 5 • Each fluorine atom has 7 valence electrons • As two atoms of Fluorine approach each other, a repulsive force occurs • The electrons repulse each other but there is also an attraction between the nuclei of each atom and the electrons • A maximum point of attraction occurs and the force of attraction balance out the forces of repulsion (most stable) • At this point, the covalent bond forms

Covalent Vocabulary • Lone pairs-the unshared pair of electrons • Bonding pair- the shared pair of electrons Ex. Look at the dot structure of F 2

Single Covalent Bonds • Formed by the sharing of one pair of electrons • Hydrogen and the halogen group elements will form single covalent bonds with an identical atom • Group 6 A elements will form two single covalent bonds (ex. H 2 O, Water) • Group 5 A will form three single covalent bonds (ex. NH 3, Ammonia)

Page 244, Practice Problems Draw the Dot Structures for these molecules: 1. PH 3 2. H 2 S 3. HCl 4. CCl 4 5. Si. H 4

Sigma Bonds • Sigma bonds are single covalent bonds • Represented by the Greek letter sigma (σ) • Occurs when electron pair is shared in an area centered between two atoms and there is an overlap in the valence orbital

Multiple Covalent Bonds • Double bonds- two pairs of electrons are shared (ex. O 2) • Triple bonds – three pairs of electrons are shared (ex. N 2) • Multiple bonds consist of a sigma bond at least one pi bond (π) • Double bond has one sigma and one pi bond • Triple bond has one sigma and two pi bonds

Strength of Covalent Bonds • Strength depends on how much distance separates the nuclei • Bond Dissociation energy • • Extra Credit Assignment – Due Dec. 1 READ PAGES 246 -247 DO page 247 6 -11 (6) READ PAGES 252 -258 DO page 258 42 -47(6) READ PAGES 259 – 262 DO page 259 54 -58 (5)

9. 2 Naming Binary Molecules 1. First element is always named first, using entire elements name 2. The second element is named with the ending –ide 3. Prefixes are added to each name to indicate the number of atoms present 4. Exception: if there is only one of the first element omit prefix

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

Page 249, 13 -17 13. CCl 4 14. As 2 O 3 15. CO 16. SO 2 17. NF 3

Page 249, Table 9 -2 Formulas and Names of Some Covalent Compounds Formulas Common Name Molecular Compound name H 2 O Water Dihydrogen monoxide NH 3 Ammonia Nitrogen trihydride N 2 H 4 Hydrazine Dinitrogen tetrahydride N 2 O Nitrous oxide Dinitrogen monoxide NO Nitric oxide Nitrogen monoxide

Naming Acids • Water solutions of some molecules are acidic (ACIDS) • If in solution, the compound produces H+ ions, then it is acidic • Example: HCl hydrochloric acid • Two Types of Acids: – 1. Binary Acids – 2. Oxyacids

Binary Acids • Contains hydrogen and one other element • When naming, use prefix hydro- to indicate the presence of hydrogen • Add the ending –ic, and then write the word acid at the end of the name. • Ex. HBr hydrobromic acid

Oxyacids • Acids containing an oxyanion such as SO 4 • In naming, do not use the hydro prefix, you will need to change the suffix on the anion – If the ending is –ate change it to –ic – If the ending is –ite change it to –ous HNO 3 nitric acid HNO 2 nitrous acid

Page 250, 18 -22 18. HI 19. HCl. O 3 20. HCl. O 2 21. H 2 SO 3 22. H 2 S

9. 3 Molecular Structures • Structural formulas use the letter symbols and the dots to illustrate relative positions of atoms • The central atom is the one with the least attractive force • Hydrogen is always terminal atom due to only sharing one possible electron Ex. NH 3

So, How do polyatomic ions form anyway? • Example: Cl. O 4 -1 PO 4 -3 NH 4+1

Resonance Structures • It is possible to have more than one correct Lewis Structure • These are called resonance structures • Ex. Nitrite ion NO 2 -1 • These are common molecules with more than one structure: ozone (O 3), nitrate, nitrite, sulfite, and carbonate

9. 4 Molecular Shape • Molecular geometry is important ot understanidng the stregth of bonds • VSEPR Model determines shape • Valence Shell Electron Pair Repulsion – Based on minimizing repulsion of shared and unshared pairs of electrons – Memorize shapes on page 260

9. 5 Electronegativity and Polarity • Polar bonds occur when electrons are not shared equally, resulting in unequal distribution of charge and the formation of a dipole • spatial arrangement of polar bonds in a molecule determines the overall polarity of a molecule