Chemistry MCQs
Topic Notes: Chemistry
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
21
Which period in the modern periodic table contains no metallic elements?
Answer:
1
The first period of the periodic table contains only Hydrogen and Helium. Hydrogen is a non-metal, and Helium is a noble gas (also a non-metal). Therefore, the first period is unique in that it lacks any metallic elements.
22
In the modern periodic table, what is the group placement for an element with an electronic configuration of 2, 8, 1?
Answer:
Group 1
The electronic configuration 2, 8, 1 indicates that the element has three shells and one valence electron. Elements with one valence electron belong to Group 1 of the periodic table, which consists of the alkali metals. The number of shells (three) determines the period (Period 3), while the valence electron count determines the group.
23
In which arrangement does the number of valence electrons increase as you move from one side to the other?
Answer:
period
Moving across a period from left to right, each successive element adds one proton and one electron to the same principal energy level. Consequently, the number of valence electrons increases by one for each step across the period.
24
Among the elements with atomic numbers 11, 13, 16, and 17, which one is the most metallic?
Answer:
11
Metallic character increases as you move from right to left across a period because the ionization energy decreases, making it easier for the atom to lose electrons. Sodium (atomic number 11) is an alkali metal in Group 1, whereas the others (13, 16, 17) are post-transition metals or non-metals. Therefore, sodium is the most metallic element in this set.
25
In the modern periodic table, which two elements flank Silicon (Z = 14) within the same period?
Answer:
Al & P
Silicon (Si) has an atomic number of 14 and is located in Period 3, Group 14. Aluminum (Al) has an atomic number of 13 and is located in Group 13, while Phosphorus (P) has an atomic number of 15 and is located in Group 15. Both are in the same period as Silicon.
26
What is the term used for the horizontal rows in the periodic table?
Answer:
Period
In the modern periodic table, the horizontal rows are referred to as periods. There are seven periods in total, and elements within the same period have the same number of occupied electron shells. In contrast, vertical columns are known as groups.
27
Which element is the third member of the Dobereiner's triad that includes lithium and sodium?
Answer:
Potassium
Johann Wolfgang Dobereiner proposed the Law of Triads, where the atomic mass of the middle element is approximately the average of the other two. The alkali metal triad consists of Lithium (Li), Sodium (Na), and Potassium (K). Potassium is the third member of this specific group.
28
Excluding helium, how many valence electrons do the final elements in each period of the periodic table typically possess?
Answer:
8 valence electrons
The elements at the end of each period are noble gases (Group 18). With the exception of helium, which has a full valence shell of two electrons, all other noble gases possess a stable octet configuration, meaning they have eight valence electrons in their outermost shell.
29
Evaluate the following statements regarding Mendeleev's periodic table: 1. The position of isotopes was not explicitly defined. 2. Mendeleev's periodic law was based on atomic mass. Which statements are correct?
Answer:
Both 1 and 2
Mendeleev's periodic table was organized primarily by increasing atomic mass. Because isotopes of the same element have different atomic masses, they did not have a distinct, fixed position in his original table. Both statements accurately reflect the historical limitations and the foundational principle of Mendeleev's work.
30
In the modern periodic table, where are the metallic elements primarily located?
Answer:
left
The modern periodic table is organized such that metals are predominantly located on the left and center sections (s-block, d-block, and f-block). Non-metals are primarily found on the upper right side of the p-block, separated by a staircase of metalloids.