Chemistry 103---Quiz #7, Friday Oct. 22, 1999

(a periodic table is included on the back)

Name _____AVERAGE = 8.5 VERY GOOD for most of you. If you have <7/10 please see me and practice, practice, practice Lewis Structures, formal charges, VSEPR this week.

  1. Arrange the following atoms in order of size (largest to smallest)

    2. P, Si, Na, and Cl. Explain your reasoning.

    Largest______Na_____ _____Si______ _____P______ ____Cl_____Smallest

    Atomic radii from left to right in the same period decrease due to the increased nuclear charge.

  2. V3+ is isoelectronic with _______Ca___ atom because _both have 20 electrons_.

    3. Isoelectronic means having the same number of electrons.

  3. Arrange the following atoms in order of first ionization energy (largest to smallest)

O, Te, S, Se. Explain your reasoning.

Largest_______O____ _______S____ ______Se_____ ____Te_____Smallest

The first ionization energy decreases from top to bottom in the periodic chart because the valence electrons are closest to the nucleus in O and furthest in Te.

Write the number of valence electrons and Lewis Structures the molecules below. Central atoms are underlined in bold.

5. Carbon monoxide, CO 4+6=10 e

:CtriplebondO:; octet rule is satisfied for both C and O. Count electrons first, then draw structure.

_____5_____ electron pairs

6. H3O+ 3+6-1=8 electrons

O has one lone pair and makes 3 single bonds to H. Remember to write the overall charge! H can never make more than one bond.

______4____electron pairs

7. OCN- 6+4+5+1=16 electrons

:O=C=N: or ::O-CtriplebondN: (O has 3 lone pairs and 1 single bond)

fc 0 0 -1 -1 0 0

the triply bonded structure is preferred becaus O is more electronegative than N so the -1 charge should be on O. Starting this week you will be expected to use formal charges!

___8___electron pairs