#13 p. 229 in the book: What electron configurations do atoms usually achieve by sharing electrons to form covalent bonds?

In forming covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.

  symbol electron configuration

helium He 1s2

neon Ne [He]2s22p6

argon Ar [Ne]3s23p6

krypton Kr [Ar]3d104s24p6

xenon Xe [Kr]4d105s25p6

radon Rn [Xe]4f145d106s26p6

The s and p orbitalsare full (8 electrons)

#14 How is an electron dot structure usedto represent a covalent bond?

An electron dot structure such as H:H (seen below)

represents the shared pair of electrons of the covalent bond by two dots

Please see the on-line textbook Chapter 8 section 2simulation 6 CHEM ASAP! “simulate the covalent bonding between molecules”

#15 When are two atoms likely to form a double bond between them? A triple bond?

Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.

Oxygen isan exampleof two atomsjoining andsharing twopairs of elect-rons to forma double bond.

Nitrogen is an exampleof two atoms joining andsharing three pairs of elect-rons to form a triple bond.

#16 How is a coordinate covalent bond differentfrom other covalent bonds?

In most cova-lent bonds eachatom contributesone electron tothe bond. In acoordinate coval-ent bond bothelectrons are contributed by the same atom

Oxygen has to “kick in” two additional electrons toallow both to have a full octet (eight total) valenceelectrons

#17 How is the strength of a covalent bond relatedto its bond dissociation energy?

A large bond dissociation energy corresponds to a strong covalent bond.

As you can see in the table on the right dif-ferent covalent bondshave different amountsof energy needed to break apart. A largedissociation energy(see N triple N) is a strong bond. A lowdissociation energy (see N-O) is a weakbond.

#18 Draw the electron dot resonance structuresfor ozone and explain how they describe itsbonding.

When you have two equally valid options for dot structureas seen above you have RESONANCE.

Click here to see a movie about how ozone is formed in the upper atmosphereand its importance in shielding the earth from Ultraviolet radiation

Click here to see a movie about how ozone is destroyed by CFC’s

#19 List three ways in which the octet rule can sometimesfail to be obeyed.

The octet rule cannot be satisfied in molecules:1. whose total number of valence electrons is an odd number. 2. There are also molecules in which an atom has FEWER THAN 8 valenceelectrons,3. Molecules with MORE than a complete octet of valence electrons.

1. Nitrogenas an ODDnumber (5)of valence electronsand thussometimesdoes not obey the octetrule

Nitrogen has only 7 valence electrons

O N O●● ●

●●

●● ●● ●● ●

●● ●●●

#19 continued

2. The boron in BF3 has a deficiency of valence electrons (only 6 total) so it doesn’t obey the octet rule

BF F

F3. In the case of PCl5 and SF6 the P and the S have MORE THAN the octet (Phas 10 and S has 12)

#20 What kinds of information does a structuralformula reveal about the compound it represents?

It reveals the way the atoms are bonded together:ie; single bonds, double bonds, triple bonds, and bond angles, unshared pairs, etc.

#21 Draw electron dot structures for the following molecules which have onlysingle covalent bonds.

H2S

SHH

PH3

HH

HP

ClF

ClF

Cl

F

# 22. Use the bond dissociation energies ofH2 (435 kJ/mole) and of a typical carbon-carbon bond (347kJ/mole) to decide which bond is stronger. Explain your reasoning.

The hydrogenbond is strongerdue to its greaterbond dissociationenergy (theamount of energyneeded to breakit.)