Unit 6 Test – Chemistry I
1. Which of the following has a bent shape?
(A) SF2
(B) SiCl4
(C) PH3
(D) CO2
REASON:
There are two unshared (lone) electron pairs on the central atom and two shared pairs
of electrons on the central atom.
2. A molecule with a trigonal pyramid shape will always be polar because
(A) trigonal pyramid molecules only live in Antarctica
(B) their surrounding atoms are never the same element
(C) there is always one unshared electron pair on the central atom
(D) there are three surrounding atoms and there is always space left at the top of the molecule
REASON: Trigonal pyramid corresponds to the AB3E shape. The “E” in the class stands for an unshared
(lone) electron pair on the central atom.
3. According to the VSEPR theory, an AB3 molecule is
(A) linear
(B) bent
(C) trigonal planar
(D) trigonal pyramid
REASON: definition of trigonal planar – corresponds to one central atom (A) with three surrounding atoms
(B) and no lone pairs of electrons on the central atom.
4. An ionic bond forms between atoms of
(A) Cl and Cl (B) P and Cl
(C) K and Cl (D) H and Cl
REASON: Ionic bonding occurs between a metal and a nonmetal.
5. The bonding in NH3 is most similar to the bonding in
(A) MgO
(B) KF
(C) H2O
(D) NaCl
REASON: NH3 has covalent bonds (between two nonmetals). So does H2O.
6. Which compound best illustrates ionic bonding?
(A) H2O
(B) CCl4
(C) MgCl2
REASON: See #4.
(D) CO2
7. Separate, individual atoms of elements are ___ stable as when they are combined with other elements.
(A) more
(B) less
(C) equally as
REASON: Elements would rather have a stable valence electron configuration like the noble gases than to
be by themselves. The way most achieve the stable configuration is through bonding with other elements.
8. Which kind of bond is formed when two atoms share electrons to form a molecule?
(A) ionic
(B) metallic
(C) electrovalent
(D) covalent
REASON: definition of covalent bonding
9. What shape are molecules that belong to classes AB2E and AB2E2?
(A) linear
(B) bent
(C) trigonal planar
(D) trigonal pyramid
REASON: these two classes correspond to a bent shaped molecule
10. The type of bond formed as a result of the transfer of electrons is called
(A) metallic
(B) ionic
(C) intermolecular
(D) covalent
REASON: definition of ionic bond
11. Given the equation: I + I  I2
As the atoms of iodine react to form molecules of iodine, the stability of the iodine
(A) increases
(B) decreases
(C) remains the same
REASON: Elements react together to achieve stable valence electron configuration by bonding with other
elements.
12. Which type of bond is usually exhibited when the electronegativity difference between two atoms is
2.1?
(A) ionic
(B) metallic
(C) nonpolar covalent
(D) polar covalent
REASON: An electronegativity difference between 0 and 0.3 is nonpolar covalent. An electronegativity
difference between 0.3 and 1.7 is polar covalent. An electronegativity difference greater than 1.7 is an ionic
bond.
13. Which formula represents a tetrahedral molecule?
(A) HBr
(B) Br2
(C) CaCl2
(D) CH4
REASON: Shortcut!!! Tetrahedral molecules have the class AB4, meaning that there is one central atom and
four surrounding atoms. CH4 is the only answer choice with four surrounding atoms. You don’t even have
to draw the Lewis structure! In a different problem, this same strategy could help you eliminate one or
more answer choices to limit the number of Lewis structures you have to draw.
14. In which of these compounds is the bond between the atoms NOT a nonpolar covalent bond?
(A) Cl2
(B) H2
(C) O2
(D) CO2
REASON: Nonpolar covalent bonds occur between two atoms of the same element. CO2 has two different
elements.
15. Which electron dot formula represents a substance that contains a nonpolar covalent bond?
(A)
REASON: See #14.
(B)
(C)
(D)
16. How many double bonds are there in the Lewis structure for nitrate, NO3-1?
(A) zero
(B) one
(C) two
(D) three
REASON:
17. In potassium bicarbonate, KHCO3, the bonds are
(A) ionic only
(B) both ionic and covalent
(C) covalent only
(D) both ionic and metallic
REASON: The compound contains a metal and more than one nonmetal. Metal and nonmetal = ionic, one
or more nonmetals = covalent.
18. Which of the following molecules contains a polar covalent bond?
(A)
(B)
(C)
(D)
REASON: polar covalent bonds occur between two different nonmetals.
19. The bond between a metal and a nonmetal is
(A) nonpolar covalent
(B) ionic
REASON: See #4.
(C) polar covalent
20. Which combination of atoms can form a polar covalent bond?
(A) H and Br
(B) N and N
(C) H and H
REASON: See #18.
(D) metallic
(D) Na and Br
21. If two covalently-bonded atoms are identical, the bond between them is
(A) nonpolar covalent
(B) ionic
(C) polar covalent
REASON: See #14.
(D) metallic
22. What element would be the central atom when drawing the Lewis structure for the compound AsI3?
(A) As
(B) I
(C) 3
(D) I3
REASON: Central atom is written first in the formula – unless first element is hydrogen.
23. Once an atom has lost or gained electrons, it is
(A) an isotope
(B) an alloy
REASON: definition of ion
(C) a polyatomic ion
24. According to the VSEPR theory, the structure of the molecule SeH2 is
(A) linear
(B) bent
(C) trigonal planar
REASON:
(D) an ion
(D) trigonal pyramid
Class = AB2E2  bent shape
25. In which compound have the electrons been transferred to the oxygen?
(A) Na2O
(B) N2O
(C) NO2
(D) CO
REASON: ionic bonding involves the transfer of electrons – ionic bonding occurs between a metal and a
nonmetal
26. Which of the following has two shared pairs and two unshared pairs of electrons on its central atom?
(A) CH4
(B) H2O
(C) NH3
(D) HF
REASON:
The red pairs are lone/unshared. The blue pairs are shared.
Tell which type of bonding each of the following describes. Mark (A) for ionic or (C) for covalent.
(A)27. transfers electrons
(C)28. occurs between nonmetals
(C)29. shares electrons
(A)30. occurs between a metal and a nonmetal
REASON: #27 - #30 are definitions