JLH Chem Ch 4 Flashcards
(106 cards)
1
Q
Most compounds that we come into contact with in our daily lives are what?
A
covalent compounds
2
Q
When two hydrogen atoms with ___ electron each combine, they form a ________ bond that contains ___ electrons.
A
When two hydrogen atoms with one electron each combine, they form a covalent bond that contains two electrons.
3
Q
When two hydrogen atoms bond they form the hydrogen molecule, H2. This is an especially stable arrangement, because why?
A
the shared electrons (from each hydrogen) give each hydrogen atom the noble gas configuration of helium.
4
Q
covalent bond
A
two electron bond in which the bonding atoms share valence electrons
5
Q
molecule
A
compound held together by covalent bonds
6
Q
what ways can a two-electron bond be drawn as?
A
7
Q
What is a diatomic molecule?
A
molecules composed of only two atoms
8
Q
What are the 7 diatomic Elements?
A
9
Q
What is an example of a diatomic molecule that has two different atoms?
A
Hydrogen fluoride (HF)
- Remember, Hydrogen is a non-metal*
- called heteronuclear diatomic molecules. When atoms are not identical, the molecule forms by combining atomic orbitals of unequal energies. The result is a polar bond in which atomic orbitals contribute unevenly to each molecular orbital.*
10
Q
What are unshared electron pairs called?
A
non-bonded electron pairs
or
lone pairs
11
Q
Draw an electron-dot symbol to show how a hydrogen atom and a chlorine atom form the diatomic molecule HCL.
A
H is surrounded by 2 electrons (same as He)
Cl is surrounded by eight electrons (same as Ar)
12
Q
When do two atoms form covalent bonds rather than ionic bonds?
A
Covalent bonds are formed when two nonmetals combine or when a nonmetal and a metalloid bond.
Nonmetals do not easily lose electrons, and as a result, one nonmetal does not readily transfer an electron to another nonmetal.
13
Q
3 examples of covalent molecules in which each main group element is surrounded by 8 electrons.
A
CH4 (methane)
NH3 (ammonia)
H2O (water)
14
Q
Lewis dot structure
A
An electron-dot structure for a molecule that shows the location of all valence electrons in the molecule, both the shared electrons in bonds and the nonbonded electron pairs.
15
Q
Atoms with one, two, or three valence electrons generally form how many bonds?
A
one, two, or three bonds, respectively
16
Q
How many bonds do atoms with 4 or more valence electrons form?
A
enough bonds to give an octet.
17
Q
How many covalent bonds are predicted for each atom:
B
N
A
B has 3 valence electrons. Thus, it is expected to form 3 bonds
N has 5 valence electrons. Because it contains more than 4 valence electrons, it is expected to form 8-5=3 bonds.
18
Q
how many covalent bonds are predicted for each atom:
F
Si
A
F: 1 bond
Si: 4 bonds
19
Q
Fill in the lone pairs
A
20
Q
Fill in the lone pairs
A
21
Q
fill in the lone pairs
A
22
Q
Living organisms are a sea of covalent molecules. Name some covalent molecules in the body.
A
Water (major component of the body)
Proteins that compose muscle
Carbohydrates that are metabolized for energy
stored fat
DNA
Hemoglobin
23
Q
What covalent compound is a building block of proteins that compose heart muscle?
A
Glycine
- Hydrogen = White.
- Oxygen = Red.
- Chlorine = Green.
- Nitrogen = Blue.
- Carbon = Grey/Black.
- Sulphur = Yellow.
- Phosphorus = Orange
24
Q
What does a molecular formula show us?
A
The number and identity of all of the atoms in a covalent compound
Does not tell us what atoms are bonded to each other.
25
The molecular formula NH3 for ammonia shows that ammonia contains one nitrogen atom and three hydrogen atoms, but it does not tell us that ammonia has three covalent nitrogen-hydrogen bonds and that the N atom has a lone pair. What type of structure shows the connectivity between the atoms?
Lewis dot structure
26
What are the 3 general rules for drawing Lewis structures?
1. Draw only the valence electrons
2. Give every main group element (except hydrogen) an octet of electrons
3. Give each hydrogen 2 electrons
27
While drawing a Lewis structure for a diatomic molecule with one bond is straightforward, drawing Lewis structures for compounds with 3 or more atoms is easier if you follow a general procedure. What is this general procedure?
Arrange the atoms next to each other that you think are bonded together. (always place hydrogens & halogens on the periphery)
However many electrons needed to form an octet on an element is usually how many bonds that element will form. (N generally forms 3 bonds-place 3 atoms around N, C generally forms 4 bonds-place 4 atoms around C)
28
How do you arrange the electrons around the atoms in a Lewis structure?
Place one bond between every 2 atoms, giving 2 electrons to each H and no more than 8 to all other main group atoms
Use all remaining electrons to fill octets with lone pairs, beginning with atoms on the periphery.
29
When drawing a Lewis structure, if all valence electrons are used and an atom does not have an octet, what do you do?
Convert one lone pair to one bonding pair of electrons for each 2 electrons needed to complete an octet. *This forms double or triple bonds.*
30
How many electrons does a single covalent bond contain?
double bond?
triple bond?
Single bond: 2 e-
Double bond: 4 e-
Triple bond: 6 e-
31
draw a Lewis structure for chloromethane, CH3CL
(Since C needs 4 e-) Place C in the center (H and Cl only need 1 e-) so place them on the periphery
Count electrons (C has 4e-, H has 3e- because there is 3 Hs, Cl has 7e-, making a total 14 e-)
Add the bonds & lone pairs
32
Draw a Lewis structure for HBr
33
Draw a Lewis structure for CH3F
34
Draw a Lewis structure for CH2CL2
35
Draw a Lewis structure for methanol (CH4O)
C needs 4 atoms around it
O needs 2 atoms around it
14 total valence electrons
36
draw a Lewis structure for dimethyl ether (C2H60) with the given arrangement of atoms
37
Sometimes it is not possible to give every main group element (except hydrogen) an octet of electrons by placing only single bonds in a molecule. For example, in drawing a Lewis structure for N2, each N has 5 valence electrons, so there are 10 electrons to place. If there is only one N-N bond, adding lone pairs gives one or both N's fewer than eight electrons. How do we fix this?
We must convert a lone pair to a bonding pair of electrons to form a multiple bond. Because we have 4 fewer electrons than needed, we must convert 2 lone pairs to 2 bonding pairs of electrons and form a triple bond.
38
Draw a Lewis structure for ethylene (C2H4)
39
Draw a valid Lewis structure for HCN
40
Draw a Lewis structure for formic acid (CH2O2) with the following arrangement of atoms:
41
Elements in group 3A of the periodic table, such as boron, do not have enough valence electrons to form an octet in a neutral molecule. What is the Lewis structure for BF3?
only 6 electrons around B
I'm just not sure why BF3 does not get a double bond *(maybe because B can only have 3 bonds)*
42
Another exception to the octet rule occurs with some elements located in the 3rd row & later. Explain-
these elements have empty d orbitals available to accept electrons, and thus they may have more than 8 electrons around them.
Most common elements in this category are phosphorus & sulfur, which can have 10 or 12 e- around them.
43
Example of using P and S getting 8 or 10 electrons
44
Two examples of compounds that have an exception to the octet rule. (has P or S)
H3PO4 phosphoric acid (10 e-)
H2SO4 sulfuric acid (12 e-)
45
Draw a Lewis structure for BBr3
does not follow the octet rule
| (has only 6 electrons around it)
46
How many valence electrons does CN- have?
10 valence e-
47
In order to give each atom in CN- an octet, the two atoms must be joined by a triple bond, and both carbon and nitrogen have a lone pair. How do we know this?
Count the electrons (C=4e-; N=5e-; 1 more e- for the negative charge = total of 10e-)
C can have up to 4 bonds; N can have up to 3 bonds
To give each atom an octet = triple bond between C & N and one lone pair on both C and N
48
resonance structure
Two Lewis structures having the same arrangement of atoms but a different arrangement of electrons.
(need a pic of resonance structures for HCO3-)
49
Draw a Lewis structure for HCO3- and show both resonance structures
total e-, including elements valence electrons and the neg or pos
50
What symbol do we often use to show that 2 Lewis structures are resonance structures?
double-headed arrow
←→
51
Which structure, A or B, is an accurate representation for HCO3-?
neither
The true structure is a composite of both resonance forms called a hybrid
52
Hybrid
composite of two or more resonance forms.
53
Resonance stabilizes a molecule by doing what?
spreading out lone pairs & electron pairs in multiple bonds over a larger region of space.
54
We say a molecule or ion that has two or more resonance structures is what?
resonance-stabilized
55
Draw 2 additional structures for tartrate
56
In addition to polyatomic ions, resonance structures can be drawn for neutral molecules. For example, the molecule ozone, O3, can be drawn as two resonance structures that differ in the placement of a double bond and a lone pair.
57
Ozone is formed in the upper atmosphere (stratosphere) by the reaction of what?
oxygen molecules (O2) with oxygen atoms (O)
58
Common Prefixes in Nomenclature for number of atoms
59
When naming a covalent molecule we name the first by its element name and then add the prefix -ide to the second element name (oxide). What else needs to be done when there are more than one of the first or second non-metal?
Use a prefix (Mono, Di, Tri, Tetra, Penta)
60
Name these covalent molecules:
NO2
N2O4
NO2: nitrogen dioxide
N2O4: dinitrogen tetroxide
61
Name each covalent molecule
NO2
N2O4
NO2: nitrogen dioxide
N2O4: dinitrogen tetroxide
62
Name each compound:
CS2
SO2
PCl5
BF3
CS2: carbon disulfide
SO2: sulfur dioxide
PCl5: phosphorus pentachloride
BF3: boron trifluoride
63
Give the formula for silicon tetrafluoride
SiF4
64
Give the formula for diphosphorus pentoxide
P2O5
65
VSEPR
valence shell electron pair repulsion
66
According to the VSEPR theory, an atom surrounded by two groups is what?
linear, with a bond angle of 180°
67
According to the VSEPR theory, an atom surrounded by three groups is what?
trigonal planar, with a bond angle of 120°
68
According to the VSEPR theory, an atom surrounded by four groups is what?
tetrahedral, with a bond angle of 109.5°
69
How do we find the geometry of HCN (hydrogen cyanide)?
Draw Lewis structure
count the groups around central atom (C). 2 groups, one H & one N surround the C.
there are no lone pairs around central atom (C)
70
What happens when there are two groups around an atom and the central atom has lone pairs (H2O)
the lone pair pushes the bonds away, making it bent
71
What is the geometry of BF3?
Trigonal planar (bond angle= 120°)
72
What is CH4 (methane) geometry?
Tetrahedral (bond angle of 109°)
73
When we represent the three-dimensional geometry of a tetrahedron on a two-dimensional piece of paper, we place two bonds in the plane of the paper, one bond in front, and one bond behind. What do we draw to represent:
## Footnote
**bonds in the plane**
**bond in front of plane**
**bond behind the plane**
bonds in the plane: **solid line**
bond in front of plane: **wedge**
bond behind the plane: **dashed wedge**
74
When we talk about groups around the central atom, what can be considered a group?
another atom
or
a lone pair of electrons
75
What does NH3 look like?
trigonal pyramidal
| (one lone pair on N)
76
common molecular shapes around atoms
77
Using the given Lewis structure, determine the shape of acetylene
Each C is surrounded by two atoms (one C & one H) and no lone pairs (two groups) linear with 180 deg
78
What is the shape of H2S
Bent
79
A) How many tetrahedral carbons does dihydroxyacetone contain?
B) How many trigonal planar carbons does it contain?
A) 2
B) 1
80
Electronegativity is a measure of an atom's attraction for electrons in a bond. The electronegativity of an atom is assigned a value from what to what?
0 to 4
*the higher the value, the more electronegative an atom is & the more it is attracted to the electrons in a bond*
81
Electronegativity increases across a row of the Periodic table as the _______ \_\_\_\_\_\_ increases (excluding the noble gases).
Electronegativity decreases down a column of the periodic table as the ______ \_\_\_\_\_\_ increases, pushing the valence electrons farther from the nucleus.
Electronegativity increases across a row of the Periodic table as the **nuclear charge** increases (excluding the noble gases).
Electronegativity decreases down a column of the periodic table as the **atomic radius** increases, pushing the valence electrons farther from the nucleus.
82
Whenever two identical atoms are bonded together, each atom attracts the electrons in the bond to the same extent. The electrons are equally shared, and the bond is said to be what?
nonpolar
83
Bonding between atoms of different electronegativity results in the unequal sharing of electrons. What is this called?
polar
*or polar covalent*
84
What are two ways the direction of polarity in a bond can be indicated?
arrow
δ with + or -
85
What is the +δ sign given to?
the less electronegative atom
86
What is the δ- sign given to?
the more electronegative atom
87
Usually, a polar bond will be one in which the electronegativity difference between 2 atoms is what?
0.5 unit or greater
88
When the electronegativity difference is larger than 1.9 units, the electrons are essentially transferred from the less electronegative element to the more electronegative element and the bond is considered what?
ionic
89
Are these polar, nonpolar, or ionic?
Cl2
HCl
NaCl
Cl2: nonpolar
HCl: polar covalent
NaCl: ionic
90
Is HF polar, nonpolar, or ionic?
polar
91
What are the 2 factors that determine if an entire covalent molecule is polar or nonpolar?
polarity of the individual bonds
overall shape
92
Is CH4 a polar or nonpolar molecule?
**nonpolar**
(all of the C-H bonds are nonpolar)
*C has an* *electronegativity of 2.5 and H is 2.1* *for a difference of 0.4.*
93
Is CH3Cl a polar or nonpolar molecule?
Polar
(contains one polar bond between Cl and C)
94
dipole
dipole moments are **applied to the distribution of electrons between two bonded atoms**. ... Molecules with a net dipole moment are polar molecules. If the net dipole moment is zero or very, very small, the bond and molecule are considered to be nonpolar.
95
With covalent compounds that have more than one polar bond, what determines the overall polarity?
**The shape of the molecule** determines the overall polarity when there is more than one polar bond.
96
If the individual bond dipoles do not cancel, is the molecule polar or nonpolar?
**polar**
*If the individual bond dipoles cancel, the molecule is nonpolar*
97
How do we determine the polarity of molecule that has two or more polar bonds?
Identify all polar bonds based on electronegativity differences
Determine the shape around individual atoms by counting groups
Decide if individual dipoles cancel or reinforce
98
How do we determine whether H2O is a polar or nonpolar molecule?
Each O-H bond is polar because the electronegativity difference between O (3.5) & (2.1) is 1.4.
Since H2O is bent around O, the two dipoles reinforce (both point up), so H2O has a net dipole; that is, H2O is a polar molecule
99
How do we determine whether CO2 is a polar or nonpolar molecule?
Each C-O bond is polar because the electronegativity difference between O (3.5) & C (2.5) is 1.0. The Lewis structure of CO2 shows that the C atom is surrounded by two groups (2 O atoms), making it linear. In this case, the two dipoles are equal and opposite in direction, so they cancel. No net dipole
100
Label the polar bonds in C2H6, and then decide if it is polar or nonpolar
*(in other words draw the Lewis structure)*
nonpolar
101
What is H2O2
Hydrogen peroxide
102
Are any of the bonds in H2O2 polar?
The O-O bond is nonpolar
both O-H bonds are polar
103
Acetaminophen (pain-reliever)
*just get a little comfortable with the*
Each O atom has 2 lone pairs
N has 1 lone pair
there are 6 polar bonds
1 tetrahedral C
2 trigonal planar C's
104
Give Lewis structure for Glycolic acid (C2H4O3)
105
Draw the Lewis structure for ethanol (C2H5OH), determine the shape around each C, and label each bond as polar or nonpolar
106
What does Vitamin B6 (C8H11NO3) Lewis structure look like?
O surrounded by 2 atoms & 2 lone pairs (bent)
C surrounded by 4 atoms (tetrahedral)
C surrounded by 3 atoms & no lone pairs (trigonal planar)
