Chem 250 Lewis Structures
The Lewis structure for ethyne (C₂H₂) shown below is incorrect. Starting from this structure, complete the correct structure.
see diagram
The reason an ionic bond forms can best be described as
the energy change for electron transfer results in a large gain in stability when the ionic bond forms.
In a covalent bond
two atoms share valence electrons and those shared electrons form the chemical bond.
Which of the following best describes what happens when an ionic bond forms?
two atoms, one atom which is more electronegative than the other, exchange electrons and the charges hold the atoms together. Correct!
A π bond could be formed from the overlap of which two orbitals?
two unhybridized p orbitals Pi bonds are formed by overlapping p orbitals.
Draw the Lewis structure of CS₂ and then determine the number of nonbonding electron pairs on the central atom.
0 is the Correct number of nonbonding electron pairs
Determine the number of valence electrons in N₂H₂ and then draw the corresponding Lewis structure.
12
Determine the number of valence electrons in SO₃ and then draw the corresponding Lewis structure (with minimized formal charges).
24
Determine the number of valence electrons in carbonate (CO₃²⁻) and then draw the corresponding Lewis structure.
24
What is the shape of the 2p orbitals?
2p orbitals have a dumbbell shape.
Draw the Lewis structure of BeCl₂ and then choose the appropriate number of valence electrons on the central atom.
4
Draw the Lewis structure for sulfate (SO₄²⁻) with minimized formal charges. How many TOTAL likely resonance structures exist for SO₄²⁻?
6
Which of the following is the correct Lewis symbol for a neutral atom of Al?
A neutral atom of Al has 3 valence electrons.
Which of the following is the correct Lewis symbol for a neutral atom of Mg?
A neutral atom of Mg has 2 valence electrons.
Single, double, or triple covalent bonds in a carbon atom are formed from
B) valence electrons.
Which of the following is the correct Lewis symbol for the calcium ion?
B. - A neutral atom of Ca has two valence electrons. In order to be isoelectronic with a noble gas, calcium will lose two valence electrons.
Which of the following is an example of an ionic bond?
K - F 0.8-4.0= -3.2. >2.0 (greater than = Ionic unless non-metal to non-metal)
A Lewis structure with placeholder elements is shown below. If the formal charge of the central atom is 0, choose the possible identities of the central atom.
S or Se
The Lewis structure of carbonate (CO₃²⁻) is shown on the left below. What is the formal charge of the highlighted atom?
-1
Based on the bond energies for the reaction below, what is the enthalpy of the reaction, in kJ? H₂(g) + N₂(g) + 2 C(g) → 2 HCN(g)
-1222 kJ BDE=[(H−H)+(N≡N)]−[2×[(H−C)+(C≡N)]]BDE=[(H−H)+(N≡N)]−[2×[(H−C)+(C≡N)]]BDE=[(432kJ)+(942kJ)]−[2×[(411kJ)+(887kJ)]]=−1222kJ You can calculate the bond dissociation energy for each species using the table. Subtract the energies of the bonds made from the energies of the bonds broken. Remember to use the coefficients from the balanced chemical reaction.
The bond dissociation energy, in kJ, to break 4 bond(s) in 1 mole of CH₄ molecules is
1644kJ 4×411kJ=1644kJ You can calculate the bond dissociation energy using the table. A bond between H and C contains 411 kJ. CH₄ contains four of these bonds. 4×411kJ=1644kJ
The bond dissociation energy, in kJ, to break 1 bond in 1 mole of CO₂ molecules is
799kJ 1×799kJ=799kJ You can calculate the bond dissociation energy using the table. A single C=O bond contains 799 kJ 1×799kJ=799kJ
Choose the structure that has the formal charge correctly assigned.
I. Formal charge can be calculated using the following equation: formal charge = [# of valence electrons] - [electrons in lone pairs + 1/2 the number of bonding electrons]. In methoxide, oxygen has 6 valence electrons, 6 electrons in lone pairs and 2 bonding electrons, therefore the formal charge = 6-[6+1/2(2)] = -1.
Which of the following ionic compounds has the largest lattice energy; that is, which has the lattice energy most favorable to a stable lattice?
MgO Compounds with large lattice formation enthalpies (lattice energies) have strong intermolecular forces, such as the ion-ion forces present in all of these options. When comparing the strength of ion-ion forces among ionic solids, those that contain smaller ions with higher charges are held together more strongly. Among these options, both of the ions in MgO have a charge of 2 (Mg²⁺ and O²⁻) whereas all of the other options contain ions with charges of +1 and -1. As a result, MgO has the strongest ion-ion intermolecular forces, and will therefore have the most stable lattice and largest lattice formation enthalpy (lattice energy).
Draw the Lewis structure of formaldehyde (H₂CO).
See Diagram
A Lewis structure for bromate (BrO₃⁻) is shown below, however, its formal charges are not minimized. Starting from this structure, complete the correct structure with minimized formal charges.
See diagram
A Lewis structure for sulfate (SO₄²⁻) is shown below, however, its formal charges are not minimized. Starting from this structure, complete the correct structure with minimized formal charges.
See diagram
Draw the Lewis structure of O₂.
See diagram
Which of the following is NOT a statement of the First Law of Thermodynamics?
The total entropy of an isolated system cannot decrease. The First Law of Thermodynamics states that energy cannot be created nor destroyed. The statement that entropy must never decrease for an isolated system is based on the Second Law of Thermodynamics.
Which of the following is always produced as a result of an energy conversion process?
heat Some portion of the energy being converted from one form to another is always lost as waste heat.
A Lewis structure for ozone (O₃) is shown on the left below. Draw another equivalent resonance structure of O₃.
see diagram
A Lewis structure for the nitrate ion (NO₃⁻) is shown on the left below. Draw another equivalent resonance structure of NO₃⁻.
see diagram
Draw the Lewis structure of ammonia (NH₃).
see diagram
Draw the Lewis structure of carbon dioxide (CO₂). +
see diagram
Which of the following is NOT a form of potential energy?
thermal Thermal energy can be measured using a thermometer. A thermometer directly measures the average kinetic energy of a substance through the calibrated thermal expansion of mercury or dyed alcohol.
A Lewis structure for a different isomer C₂H₂F₂ is shown below. Based on this structure, determine if the molecule is polar or nonpolar.
Nonpolar Correct, the dipole from the fluorines on opposite side of the plane cancel each other out and cause no net dipole for the molecule
Draw the Lewis structure of methane (CH₄).
See diagram
Based on the law of conservation of energy, the ___ of potential and kinetic energy is constant.
Sum The sum of kinetic and potential energy is constant. For example, a ball on a track has only potential energy before it starts rolling, and an equivalent amount of kinetic translational and rotational energy at the bottom of the track.
Which one of the following trends appears when considering lattice energies?
The higher the charge on the ions, the higher the lattice energy. Consider the charge on the ions. The higher the charges, the higher the lattice formation enthalpy (lattice energy).
What is the correct molecular geometry of NH₃ according to Valence Shell Electron Pair Repulsion Theory?
Trigonal pyramidal (pyramidal). Ammonia has three groups and one set of lone pairs bound to a central atom, which affords a trigonal pyramidal, or pyramidal, molecular geometry based on Valence Shell Electron Pair Repulsion Theory.
A Lewis structure with placeholder central atom is shown below. If the charge of the molecule is -1, choose the possible identity or identities of the central atom.
Cl, Br, or I
Which atom in the Br-F molecule has a partial negative charge (δ⁻)?
F - Partial charges are determined by the relative electronegativities of the atoms in a molecule; the more electronegative atom, which is F, has a partial negative charge.
The calorie is defined based on the specific heat capacity of what substance?
H2O One calorie (c) is defined as the amount of heat required to raise the temperature of 1 gram of water by 1°C. Water has a high specific heat capacity for a small molecule due to its intermolecular hydrogen bonding.
Which of the following bonds is the most polar?
Rb- BR Elements that are located far away from each other on the periodic table have larger electronegativity differences and therefore make more polar bonds. Of all the element pairs listed, Rb and Br are the farthest apar
Which one of the following is the correct set of Lewis Symbols for CaCl₂?
The calcium ion its two valence electrons to have a 2+ charge. The chlorine ions each gain an electron to fill their octets and have a -1 charge.
Based on the law of conservation of energy, which of the following describes the transformation of energy in a diesel engine?
chemical energy to kinetic energy and heat Through the process of combustion, a diesel engine converts chemical energy into mechanical energy. Some energy is lost as heat, as with any energy conversion.
What type of property is heat?
extensive physical property Unlike temperature, which measures average kinetic energy, heat measures internal energy and depends on the amount of substance present. Therefore, it is an extensive physical property.
draw the Lewis structure of H₂O₂. Determine the number of valence electrons in hydrogen peroxide (H₂O₂) and then draw the corresponding Lewis structure.
figure this out
Heat is an example of what type of energy?
kinetic Heat measures the total molecular motion of a substance, and is therefore a form of kinetic energy. Unlike temperature, which measures average kinetic energy, heat depends on the amount of substance present.
Which set of hybrid orbitals is represented by the picture below?
sp This is an image of an sp hybrid orbital.
When molecules absorb heat, there is an increase in
the kinetic energy of the molecules. When molecules absorb heat, there is an increase in the kinetic energy of the molecules because the molecules move faster.
The Lewis structure of N₂O is shown on the left below with numbers on the corresponding atoms. Choose the correct set of formal charges of the atoms in ascending order of atom number.
#1 = 0, #2 = +1, #3 = -1
Determine the number of valence electrons in cyanide (CN⁻) and then draw the corresponding Lewis structure. Please place the elements in the order that they are written.
10 C=4 + N =5 + 1 (for negative charge)
Chloroform (CHCl₃) is an important laboratory solvent with a relatively high vapor pressure at room temperature. Draw the Lewis structure of CHCl₃ and then determine the ideal bonding angle(s) for the Cl-C-Cl bond(s).
109.5°
Determine the number of valence electrons in hydrogen peroxide (H₂O₂) and then draw the corresponding Lewis structure.
14
Convert 475 Calories to Joules
1990 J
Determine the number of valence electrons in PCl₃ and then draw the corresponding Lewis structure. A) 23 B) 24 C) 30 D) 27 E) 26
26
Which atomic orbitals from carbon hybridize to form the bonds in CH₄?
2s, 2p_x, 2p_y, 2p_z Draw the orbital energy diagram for C to find where its valence electrons are. They are found in 2s,2pₓ,2py,2pz2s,2pₓ,2py,2pz.
Determine the number of valence electrons in SiF₄ and then draw the corresponding Lewis structure. A) 31 B) 35 C) 32 D) 30 E) 36
32
How many π bonds are in the structure of the organic molecule below?
4 Remember a double bond contains 1 σ + 1 π. This molecule contains 4 double bonds, and therefore 4π.
The bond dissociation energy, in kJ, to break 1 hydrogen-carbon bond(s) in 1 mol of HC≡CH molecules is
411kJ .You can calculate the bond dissociation energy using the table. A C-H bond contains 411 kJ. Multiply the number of bonds by the dissociation energy.
Which of the following is the correct Lewis symbol for a neutral atom of O?
A neutral atom of O has 6 valence electrons.
