Review Questions for test on Chapter 12 chemical bonds
1. What is a chemical bond ?
A force that holds 2 or more atoms together
2. What does bond energy represent?
The energy needed to break a chemical bond
3. What is an ionic bond?
a covalent bond?
a polar covalent bond?
Ionic – transfer of election
Covalent – equal sharing of electrons
Polar covalent – unequal sharing of electrons
4, How does bonding in NaCl differ from bonding in Cl 2 ?
NaCl is an ionic bond – look at electroneg. Difference – Na xfers an electron to Cl
Cl2 is a covalent bond – electrons are shared between the two atoms – no diff in electroneg.
5. What is electronegativity?
The ability of an atom to pull electrons toward itself
6. What does it mean to say that a bond is polar? that a molecule is polar?
Bond – identifiable areas of + and - charge poles in the bond between 2 atoms
Molecule – same is true but at the level of the molecule
7. In each group, which element is most electronegative? which element is least electronegative?
Higher number= more electoneg. Lower # = less electroneg.
K, Na, H .8, .9, 2.1
F, Br, Na
4, 2.8, .9
B, N, F 2, 3, 4
Rb, Sr, I
.8, 1, 2.5
Ca, Mg, Sr 1, 1.2, 1
8. Indicate whether the bond is Ionic, covalent, or polar covalent
look at the difference in electron. Diff=0 covalent
diff>= 1.7 ionic
O–O
Covalent
Al – O
ionic
B–O
polar
K – Cl
ionic
9. Indicate whether the molecule contains polar covalent bonds
H 2O
O-H polar covalent 3.5- 2.1 = 1.4
CO
C-O polar covalent 2.5 – 3.5 = 1
F2
F-F covalent difference is 0
NH3
N – H polar covalent 3-2.1= .9
Br – Cl
polar cov
in between polar covalent
Cl - Cl
covalent
CH4
HBr
C –H pol ar covalent 2.5 – 2.1 = .4
Br –H polar covalent 2.8 – 2.1 = .7
10. Which is the more polar bond in the following pairs? these are all bonds between non-metals
Compare the size of the difference between each pair of bonds – the one with the greater difference is the more polar
1.9
.9
H – F or H – Cl
.9
.4
H – Cl or H – I
.5
.7
O – Cl or O – Br
.7
.9
H – Br or H – Cl
.4
1.4
P – S or P – O
.4
.7
H – I or H – Br
1.4
.9
H – O or H – N
11. Which bond has greater ionic character? these are all ionic compounds metals and nonmetals
Compare the difference in electronegativity of the bonds – the larger it is – more ionic in character
3.1
1.6
Na F or Na I
1.5
2.5
Ca S or Ca O
1.8
.9
Mg N or Mg P
2.5
3.1
BeF or BaF
.7
2.2
Fe I or Fe F
2
2.1
Li Cl or Cs Cl
12. section 12.3 in the text Why is the presence of a dipole moment in water so important? What properties of water are
determined by its polarity?
Dipole moment means that it is a polar molecule – one end slightly + one end slightly –
Negative end of one water molecule attracts the positive end of another water molecule
Evaporates and boils requires more energy than nonpolar molecules – surface tension
13. Which end is negative relative to the other end?
The end of the bond with higher electronegativity is more negative
H-C
C–O
Br –F
H–F
I- Cl
14. Draw a figure representing the direction of the bond dipole moment.
The end of the bond with higher electronegativity gets the arrow, positive end the +
+>
+>
+>
+>
+>
+>
C–F
Si – C
C–O
B–C
S- F
S–N
15. What simple ion would each of the following elemtns be expected to form?
Column 1 - -1
Cl -1
Sr
column 2 - -2
+2
O
column 3
-2
-3
Rb +1
or look at the elec config 2s1 +1
Br
-1
P -3
2
5
2s 2p -1
S -2
a
16. Give the symbol of
positive ion that could form with this number of electrons:
The orginal element would have lost electrons to form an ion. If the number is 10e- and the ion lost one to become 10, the original
element would have had 11 electrons - Na
2 e-
Li, Be
10 e-
Na, Mg,Al
18 e-
K, Ca
36 e- Rb, Sr
17. Give the symbol of a negative ion that could form with this number of electrons:
The orginal element would have gained electrons to form an ion. If the number is 10 e- and the ion gained one electron, the
original atom would have 9 – F
10 e- F, O, N
18 e- P,S,Cl
36 e- As, Se, Br
17. Predict the formula of a simple binary ionic compound that would from from these pairs of elements
Find charge on +ion, charge on – ion – use crisscross to find formula
Al S
Ra O
Ca F
Cs N
+3 2+2 -2
+2 -1
+1 3Al2S3
RaO
CaF2
Cs3N
18. Which has a smaller radius? see chart in the text – look for the pattern
positive ions have lost electrons and shrink when they do losing electrons from the s orbitals – negative electrons cause atoms
forming ions to get larger as the fill the p orbitals
Na+ or ClNa or Na+1
N
or N3Al or Al 3+
Li+ or FSmaller
smaller
smaller
smaller
smaller
18. Name the noble gas that has the same electron configuration as each ion in these compounds
For + ions previous noble gas
For - ions next noble gas
Li Cl
Li+1
He
Cl -1
Ar
Na Cl
Na +1 Cl -1
KF
K +1 F-1
Ne
Ar
Ar
Ne
Na Br
Na +1
Ne
Br -1
Kr
19. What are the duplet and octet rules?
H needs 2 e- to fill the 1s orbital
Almost all other elements need 8 electrons to be shared – we just go with 8 for all except H
20. What type of structure (electron configuration) must each atom in a compound usually exhibit for the compound to be
stable?
The electron structure of a noble gas
21. How many electrons are involved when two atoms in a molecule are connected by double bond? by a triple bond?
Double – 4
triple – 6
22 Write the Lewis structure for
N 5 dots
23. What are the total number of valence electrons in
B 3 dots
Mg- 2
C 4 dots
Ca-2
Na 1 dot
Br -7
Cl -7
24. Give the total number of valence electrons in
H2Se
NO 2 N-5+O-6+O-6=17
H-1 + H-1 + Se-6 = 8
25. Write the Lewis structure for these – show bonding electron pairs as lines, nonbonding pairs as dots
NF3
SiCl4
371 × 337 - imgarcade.com
CHCl3
300 × 169 - janetcoonce.com