Question 1

Which of the following best explains why the second ionization energy of sodium ($$\mathrm{Na}) is $$much higher than its first ionization energy?

Accepted Answer

The second electron is removed from a noble gas core, which is much more stable.

Question 2

Which of the following compounds contains both ionic and covalent bonds?

Accepted Answer

$$\mathrm{NH_4NO_3} ($$ammonium nitrate)

Question 3

Given the following mass percentages for a compound: 40.0\% C, 6.7\% H, and 53.3\% O, what is the empirical formula?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 4

Which of the following best describes why the formation of a covalent bond is exothermic?

Accepted Answer

The potential energy of the bonded atoms is lower than that of the separated atoms due to electron sharing.

Question 5

Which of the following molecules is polar, based on its Lewis structure and VSEPR shape?

Accepted Answer

$$\mathrm{NH_3$} ($$ammonia)

Question 6

Which of the following best explains why ozone ($$\mathrm{O_3$}) $$can absorb UV-B radiation while $$\mathrm{O_2$}$$ cannot?

Accepted Answer

Ozone has resonance structures that allow for electron delocalization, enabling absorption of UV-B.

Question 7

What is the formal charge on the central nitrogen atom in the Lewis structure of $$\mathrm{NO_3$^-} ($$nitrate ion)?

Accepted Answer

0

Question 8

Which of the following best describes the difference between a sigma ($$\sigma) $$bond and a pi ($$\pi) $$bond?

Accepted Answer

A $$\sigma$$ bond results from head-on overlap of orbitals, while a $$\pi$$ bond results from side-by-side overlap.

Question 9

Which of the following molecules contains sp$$^2$$ hybridized carbon atoms?

Accepted Answer

$$\mathrm{C_2H_4} ($$ethylene)

Question 10

Which of the following best explains why $$\mathrm{He_2$}$$ does not exist as a stable molecule, according to molecular orbital theory?

Accepted Answer

The number of electrons in antibonding orbitals cancels the bonding effect, resulting in a bond order of zero.

Question 11

A sample contains 18.0 g of water ($$\mathrm{H_2O}). $$How many molecules are present in the sample? (Molar mass of $$\mathrm{H_2O} = 18.0 g/$$mol)

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 12

Which of the following best describes the effect of lone pairs on molecular geometry according to VSEPR theory?

Accepted Answer

Lone pairs occupy more space than bonding pairs, causing bond angles to decrease.

Question 13

Which of the following is the correct formula for iron(III) sulfate?

Accepted Answer

$$\mathrm{Fe_2$(SO_4$)_3}$$

Question 14

Which of the following statements about bond energies and bond lengths is correct?

Accepted Answer

Triple bonds are shorter and stronger than single bonds.

Question 15

Which of the following best describes the role of cis- and trans- isomers in the chemistry of vision?

Accepted Answer

Light-induced conversion between cis- and trans- isomers triggers a signal in the visual process.

Question 16

Which of the following best describes constructive interference in the context of chemical bonding?

Accepted Answer

It increases electron density between nuclei, leading to bond formation.

Question 17

What is the molecular formula of a compound with an empirical formula of $$\mathrm{CH_2$}$$ and a molar mass of 56 g/mol? (Molar mass of $$\mathrm{CH_2$} = 14 g/$$mol)

Accepted Answer

$$\mathrm{C_4H_8}$$

Question 18

Which of the following best explains why measurements of molecular shape account only for nuclei and not for lone pair electrons?

Accepted Answer

Lone pairs are not located at fixed positions in space and do not contribute to the observed shape.

Question 19

Which of the following is the correct name for $$\mathrm{P_2O_5}$$?

Accepted Answer

Diphosphorus pentoxide

Study Guide: Atomic Properties, Chemical Bonding, and Molecular Structure

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