Question 1

Which of the following statements best explains why the first ionisation energy decreases as you move down Group 1 in the periodic table?

Accepted Answer

The outer electrons are further from the nucleus and experience more shielding, making them easier to remove.

Question 2

Given the following electronic configuration: $$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^1$$, which element does this represent and in which block of the periodic table is it found?

Accepted Answer

Aluminum, p-block

Question 3

Which isotope of magnesium would produce a peak at $$m/z = 24 in a $$mass spectrum?

Accepted Answer

$$^{24}Mg^+$$

Question 4

Why does sulfur have a lower first ionisation energy than phosphorus, despite having more protons?

Accepted Answer

Sulfur's outer electron is paired in a 3p orbital, causing electron-electron repulsion and making it easier to remove.

Question 5

Calculate the relative atomic mass (RAM) of chlorine given the following isotopic abundances: $$^{35}Cl (75$$%) and $$^{37}Cl (25$$%). Use the formula $$RAM = \frac{(isotopic\ mass 	imes \%\ abundance)}{100}.$$

Accepted Answer

$$35.5$$

Question 6

Which of the following best describes the trend in atomic radius across Period 3 (Na to Ar)?

Accepted Answer

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

Question 7

A mass spectrometer is used to analyze a sample of bromine. If the two isotopes $$^{79}Br$$ and $$^{81}Br$$ are present in equal abundance, what is the expected $$m/z$$ value for the most abundant molecular ion peak of $$Br_2$$^+$$?

Accepted Answer

$$160$$

Question 8

Which of the following is the correct order of filling for the sublevels according to increasing energy?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p$$

Question 9

Which of the following uses of mass spectrometry is most relevant to planetary science?

Accepted Answer

Identifying elements and isotopic composition on other planets.

Question 10

Why is the second ionisation energy of an element always higher than the first?

Accepted Answer

The remaining electrons experience a greater attraction to the nucleus after the first electron is removed.

Question 11

Which of the following elements is classified as a d-block element?

Accepted Answer

Iron (Fe)

Question 12

A sample of magnesium is analyzed in a mass spectrometer. If a $$^{24}Mg$$^{2+}$$ ion is detected, what will be its m/z$ value?

Accepted Answer

$$12$$

Question 13

Which of the following best explains why isotopes of the same element have nearly identical chemical properties?

Accepted Answer

They have the same electronic structure.

Question 14

Which of the following best describes the bonding and melting point trend for silicon in Period 3?

Accepted Answer

Macromolecular structure with strong covalent bonds, resulting in a very high melting point.

Question 15

Which of the following electronic configurations represents a chloride ion ($$Cl^-$$)?

Accepted Answer

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

Question 16

Which of the following best explains the small drop in first ionisation energy from magnesium to aluminum?

Accepted Answer

Aluminum's outer electron is in a higher energy 3p subshell, which is slightly shielded by the 3s electrons.

Question 17

Which of the following is the correct definition of first ionisation energy?

Accepted Answer

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge.

Question 18

Which of the following best describes the trend in melting points across Period 3 from sodium to argon?

Accepted Answer

Melting points increase from sodium to silicon, then decrease sharply from phosphorus to argon.

Question 19

Which of the following is the correct formula for calculating the relative atomic mass (RAM) using relative abundances?

Accepted Answer

$$RAM = \frac{\sum (isotopic\ mass 	imes \ relative\ abundance)}{total\ relative\ abundance}$$

Atomic Structure, Periodicity, and the Periodic Table: Study Notes for General Chemistry

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