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
1
In the modern periodic table, which period contains the elements with atomic numbers ranging from 19 to 36?
Answer:
4
The fourth period of the periodic table begins with Potassium (atomic number 19) and ends with Krypton (atomic number 36). This period includes the s-block elements (K, Ca), the d-block transition metals (Sc through Zn), and the p-block elements (Ga through Kr), totaling 18 elements.
2
Which scientist's periodic classification system was notable for predicting the existence and properties of then-undiscovered elements?
Answer:
Mendeleev
Dmitri Mendeleev famously left gaps in his periodic table for elements that had not yet been discovered. By analyzing the trends of known elements, he accurately predicted the properties of elements like gallium, scandium, and germanium, which provided strong evidence for the validity of his periodic law.
3
Identify the German chemist who proposed the classification of elements into groups of three, known as triads, in 1817.
Answer:
Johann Wolfgang Dobereiner
Johann Wolfgang Dobereiner was a German chemist who observed that certain groups of three elements, which he called triads, exhibited similar chemical properties. He noted that the atomic weight of the middle element was approximately the average of the atomic weights of the other two. This was one of the earliest attempts to classify elements based on their properties and atomic masses.
4
Which of the following sets of elements, with atomic numbers 2, 3, 7, 10, and 30, belong to the same period?
Answer:
B, C, D
Elements B (Z=3, Lithium), C (Z=7, Nitrogen), and D (Z=10, Neon) all belong to the second period of the periodic table, as they have electrons filling the n=2 shell.
5
Which of the following statements regarding the modern periodic table is incorrect?
Answer:
Elements that have atomic numbers from 57 to 70 are called lanthanide series
The lanthanide series consists of elements with atomic numbers 58 to 71 (Cerium to Lutetium). Lanthanum (atomic number 57) is often grouped with them due to chemical similarity, but the series technically begins at 58. Therefore, the statement claiming the series is 57-70 is technically inaccurate in standard chemical nomenclature.
6
How many elements are contained within the second and third periods of the periodic table?
Answer:
8 elements
The second period contains 8 elements (Lithium to Neon), and the third period also contains 8 elements (Sodium to Argon). These periods are considered 'short periods' because they only involve the filling of s and p orbitals.
7
According to Newlands' Law of Octaves, which element, despite sharing properties with cobalt and nickel, was placed far away from them?
Answer:
Fe
Newlands' Law of Octaves failed to account for the transition metals correctly. Iron (Fe) is a metal that exhibits chemical properties similar to cobalt and nickel. However, in Newlands' arrangement, iron was placed in a different group, specifically with oxygen and sulfur, which was a major flaw in his classification system.
8
What is the first element found in group 17 of the modern periodic table?
Answer:
fluorine
Group 17, also known as the halogen group, begins with Fluorine (atomic number 9) at the top of the column.
9
Which scientist proposed the classification of elements based on their atomic numbers?
Answer:
Moseley
Henry Moseley discovered the relationship between X-ray spectra and atomic number. His work demonstrated that atomic number is a more fundamental property than atomic mass for organizing the periodic table, leading to the modern periodic law.
10
In Mendeleev's periodic table, where was iodine placed despite having a lower atomic weight than tellurium?
Answer:
fluorine, chlorine and bromine
Mendeleev prioritized chemical properties over strict adherence to increasing atomic weight. Iodine (I) has chemical properties similar to the halogens (fluorine, chlorine, and bromine). Even though its atomic weight was slightly lower than tellurium (Te), Mendeleev placed iodine in the halogen group to ensure that elements with similar chemical behaviors were grouped together.