Review Questions for test on Chapter 12 chemical bonds
- What is a chemical bond ?
A force that holds 2 or more atoms together
- 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 Cl2 ?
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 in between polar covalent
O – O Al – O B – O K – Cl Br – Cl Cl - Cl
Covalent ionic polar ionic polar cov covalent
9. Indicate whether the molecule contains polar covalent bonds
H2O 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
CH4 C –H pol ar covalent 2.5 – 2.1 = .4
HBr Br –H polar covalent 2.8 – 2.1 = .7
- 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 .9 .4 .7 .9 .4 .7
H – F or H – Cl H – Cl or H – I H – Br or H – Cl H – I or H – Br
.5 .7 .4 1.4 1.4 .9
O – Cl or O – Br P – S or P – O H – O or H – N
- 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 1.5 2.5 .7 2.2 2 2.1
Na F or Na I Ca S or Ca O Fe I or Fe F Li Cl or Cs Cl
1.8 .9 2.5 3.1
Mg N or Mg P BeF or BaF
- 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
- 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
- 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
- What simple ion would each of the following elemtns be expected to form?
Column 1 - -1 column 2 - -2 column 3 -3 or look at the elec config 2s1 +1 2s22p5 -1
Cl -1 Sr +2 O -2 Rb +1 Br -1 P -3 S -2
- Give the symbol of apositive 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
- 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 3-
Al2S3 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 Cl- Na or Na+1 N or N3- Al or Al 3+ Li+ or F-
Smaller smaller smaller smaller smaller
- 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 Na Cl KF Na Br
Li+1 Cl -1 Na +1 Cl -1 K +1 F-1 Na +1 Br -1
He Ar Ne Ar Ar Ne Ne Kr
- 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
- 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
- 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 B 3 dots C 4 dots Na 1 dot
23. What are the total number of valence electrons in Mg- 2 Ca-2 Br -7 Cl -7
24. Give the total number of valence electrons in NO2 N-5+O-6+O-6=17
H2Se H-1 + H-1 + Se-6 = 8
- Write the Lewis structure for these – show bonding electron pairs as lines, nonbonding pairs as dots
NF3
SiCl4
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CHCl3
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