Q: A sample of chlorine gas contains two isotopes: $$^{35}\mathrm{Cl}$$ and $$^{37}\mathrm{Cl}. If $$the relative abundances are 75% and 25% respectively, what is the relative atomic mass ($$A_r) of $$chlorine? Use the formula $$A_r = \sum (\text{isotopic mass} \times \text{fractional abundance}).$$

$$A_r = (35 \times 0.75) + (37 \times 0.25) = 35.5$$

Question 1

Which of the following statements best explains why the first ionization energy of oxygen is lower than that of nitrogen, despite oxygen having a higher nuclear charge?

Accepted Answer

Oxygen's outermost electron is paired in a 2p orbital, increasing electron-electron repulsion.

Question 2

A sample of chlorine gas contains two isotopes: $$^{35}\mathrm{Cl}$$ and $$^{37}\mathrm{Cl}. If $$the relative abundances are 75% and 25% respectively, what is the relative atomic mass ($$A_r) of $$chlorine? Use the formula $$A_r = \sum (	ext{isotopic mass} 	imes 	ext{fractional abundance}).$$

Accepted Answer

$$A_r = (35 	imes 0.75) + (37 	imes 0.25) = 35.5$$

Question 3

Which of the following best describes the trend in atomic radius across a period from left to right in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing nuclear charge pulling electrons closer.

Question 4

A mass spectrometer separates ions based on their mass-to-charge ratio ($$m/z). $$Which ion will be deflected the most in the magnetic field?

Accepted Answer

An ion with a small mass and a double positive charge.

Question 5

Which of the following electronic configurations correctly follows Hund’s rule for the element nitrogen ($$Z=7$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ 2p_$$x^1$$\ 2p_$$y^1$$\ 2p_$$z^1$$

Question 6

Which of the following factors does NOT contribute to the decrease in first ionization energy as you move down a group in the periodic table?

Accepted Answer

Increase in nuclear charge

Question 7

Given the successive ionization energies of sodium: $$496, 4563, 6913, 9544, 13352, 16611, 20115, 25491, 28934, 141367, 159079 kJ/$$mol, which electron is being removed at the 10th ionization energy?

Accepted Answer

An electron from the first quantum shell (n=1)

Question 8

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

Question 9

Which element would you expect to have the highest first ionization energy in Period 2 of the periodic table?

Accepted Answer

Neon

Question 10

Which of the following best explains why the melting and boiling points of elements with giant lattice structures are higher than those with simple molecular structures?

Accepted Answer

Giant lattice structures have strong covalent or metallic bonds that require more energy to break.

Question 11

Which of the following is the correct order of filling for the first four electron sub-shells according to the Aufbau principle?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s$$

Question 12

Which of the following best describes the s-orbital?

Accepted Answer

Spherical shape, can hold up to 2 electrons

Question 13

Which of the following is the correct electronic configuration for potassium ($$Z=19$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$4s^1$$

Question 14

Which of the following best explains the large jump in ionization energy between the 1st and 2nd ionization energies of sodium?

Accepted Answer

The second electron is removed from a shell closer to the nucleus with less shielding.

Question 15

Which of the following is NOT a property that regularly repeats (is periodic) across the periodic table?

Accepted Answer

Number of protons in an isotope

Question 16

Which of the following best describes the trend in first ionization energy across a period?

Accepted Answer

It generally increases due to increasing nuclear charge and decreasing atomic radius.

Question 17

Which of the following is the correct formula for calculating the relative molecular mass ($$M_r) of a $$diatomic molecule from isotopic abundances?

Accepted Answer

$$M_r = \sum (	ext{isotopic mass of atom 1} 	imes 	ext{abundance}) + (	ext{isotopic mass of atom 2} 	imes 	ext{abundance})$$

Question 18

Which of the following is true about the d-block elements in the periodic table?

Accepted Answer

Their highest energy electrons are in the s orbital.

Question 19

Which of the following best explains why the van der Waals radius is larger than the covalent radius for noble gases?

Accepted Answer

Noble gases do not form covalent bonds, so the van der Waals radius measures the distance between non-bonded atoms.

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