Question
Which statement best explains the first ionization energy of sulfur being lower than that of phosphorus?
A. Sulfur has more protons than phosphorus.
B. Phosphorus does not have paired electrons in the outer p sub-level.
C. Sulfur has an unpaired electron in the outer p sub-level.
D. Phosphorus is more reactive than sulfur.
▶️Answer/Explanation
Markscheme : B
Ionization energy is the energy required to remove an electron from an atom. When moving across a period in the periodic table (from left to right), the ionization energy generally increases. This is because, as you move to the right, there are more protons in the nucleus, leading to a stronger attraction between the electrons and the nucleus.
However, there are exceptions, and one notable exception is the case of paired electrons. In the outer p sub-level, having paired electrons provides some extra stability, making it slightly easier to remove an electron. Phosphorus has a paired electron in its outer p sub-level, making its first ionization energy slightly lower than that of sulfur.
So, option B is the correct explanation.
Question
What can be deduced from the period number of an element?
I. Highest occupied energy level
II. Number of sub-levels in the outer shell
III. Number of outer electrons
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Markscheme: A
The period number of an element corresponds to the highest occupied energy level (shell) of its electrons. Therefore, from the period number, you can deduce:
I. Highest occupied energy level – Yes, this is correct.
II. Number of sub-levels in the outer shell – The period number alone does not provide information about the number of sub-levels in the outer shell. This information is related to the specific electron configuration of the element.
III. Number of outer electrons – The period number can give you a rough idea of the number of outer electrons. For elements in a given period, the outer electrons are found in the same principal energy level. However, the specific number of outer electrons depends on the element’s position within the period.
Therefore, the correct answer is A. I and II only.
Question
Which element is not a transition metal?
A. Cr
B. Mn
C. Ni
D. Zn
▶️Answer/Explanation
>Markscheme: D
The transition metals are typically found in the middle of the periodic table, spanning groups 3 to 12 . Zinc \((\mathrm{Zn})\) is not considered a transition metal. It is located in group 12 and is considered a post-transition metal.
Question
Why does the melting point of the elements decrease down group 1?
A. Atomic mass increases
B. Number of electrons increases
C. Radius of metal ion increases
D. First ionization energy decreases
▶️Answer/Explanation
Markscheme: C
The correct answer is C. Radius of metal ion increases.
Down Group 1 (alkali metals), as you move from the top (e.g., lithium) to the bottom (e.g., cesium), the size of the atoms increases. This is due to the addition of new electron shells as you go down the group. As the atoms get larger, the outer electrons are farther from the nucleus, and the attractive forces between the electrons and the nucleus become weaker.
The weakening of these forces results in a decrease in the melting point down Group 1. The outer electrons are held less tightly by the nucleus, making it easier for the metal atoms to overcome the attractive forces and transition into the liquid phase.
So, the correct choice is C. Radius of metal ion increases.
Question
Which molecule produces this \(^1H-NMR\) spectrum?
A. \(CH_3COOCH_3\)
B. \(CH_3COCH_3\)
C. \(CH_3CHO\)
D. \(CH_3CH_2CH_3\)
Answer/Explanation
Markscheme: B