Q: What is the formal charge formula for an atom in a Lewis structure?

$$\text{Formal charge} = (\text{valence electrons in free atom}) - (\text{number of lone pair electrons}) - \frac{1}{2}(\text{number of bonding electrons})$$

Question 1

Which of the following best describes a polar covalent bond?

Accepted Answer

A bond in which electrons are shared unequally between two atoms.

Question 2

Which of the following molecules will align with an external electric field due to its bond polarity?

Accepted Answer

HF

Question 3

Electronegativity is defined as:

Accepted Answer

The ability of an atom to attract shared electrons in a covalent bond.

Question 4

Which of the following correctly lists the elements in order of increasing electronegativity (least to most)?

Accepted Answer

C \u003c N \u003c O \u003c F

Question 5

What is the relationship between bond length and bond strength?

Accepted Answer

Shorter bonds tend to be stronger than longer bonds.

Question 6

Which bond is most polar?

Accepted Answer

P-F

Question 7

A 246 nm photon has just enough energy to break the C-Cl bond in CCl$$_4. $$What is the bond energy in kJ/mol for the C-Cl bond? (Use $$E = \frac{hc}{\lambda}$$ and $$1$$ mol $$= 6.022 	imes 10$$^{23}$$ photons)

Accepted Answer

$$243 kJ/$$mol

Question 8

Which type of radiation causes vibrational excitation in molecules?

Accepted Answer

Infrared radiation

Question 9

For a vibrational mode to be IR active, what must occur?

Accepted Answer

The vibration must cause a change in the dipole moment of the molecule.

Question 10

Which of the following is a consequence of the greenhouse effect?

Accepted Answer

Absorption and re-emission of infrared energy by CO$$_2$$ and other greenhouse gases.

Question 11

Which statement about resonance structures is correct?

Accepted Answer

The actual structure is an average of the resonance structures.

Question 12

What is the formal charge on the central carbon atom in the best Lewis structure for CO$$_2$$?

Accepted Answer

$$0$$

Question 13

Which of the following is NOT a criterion for the best resonance structure?

Accepted Answer

Positive charges on the most electronegative atom.

Question 14

Which of the following is an exception to the octet rule?

Accepted Answer

Molecules with free radicals (odd number of electrons).

Question 15

Which element is most likely to form hypercoordinate molecules?

Accepted Answer

Phosphorus

Question 16

What is the formal charge formula for an atom in a Lewis structure?

Accepted Answer

$$	ext{Formal charge} = (	ext{valence electrons in free atom}) - (	ext{number of lone pair electrons}) - \frac{1}{2}(	ext{number of bonding electrons})$$

Question 17

Which molecule is an example of an incomplete octet?

Accepted Answer

BF$$_3$$

Question 18

Why can't the octet rule be satisfied for free radicals?

Accepted Answer

They have an odd number of electrons.

Question 19

Which of the following is true about electrons in resonance bonds?

Accepted Answer

They are delocalized over multiple atoms.

Electronegativity, Bond Polarity, and Covalent Bond Energies: Study Notes

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