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
11
Which scientist is credited with the development of the modern periodic table based on atomic number?
Answer:
M.J. Moseley
Henry Moseley discovered the relationship between atomic number and X-ray spectra. This fundamental discovery allowed for the arrangement of elements by atomic number rather than atomic mass, which resolved inconsistencies in Mendeleev's original table and formed the basis of the modern periodic law.
12
Which scientist is credited with proposing the 'Law of Octaves' in the context of early periodic classification?
Answer:
Alexander Newlands
John Alexander Reina Newlands proposed the Law of Octaves in 1865. He observed that when elements are arranged in increasing order of their atomic weights, the properties of every eighth element are a repetition of the first, similar to the octaves in music. This was a significant early attempt at organizing elements based on periodicity, though it only worked well for lighter elements.
13
Which scientist is primarily credited with the early classification of elements based on their atomic masses?
Answer:
Dmitry Mendeleev
While others like Dobereiner and Newlands also used atomic mass, Mendeleev is most famously credited for his comprehensive periodic table based on atomic mass. He organized elements into groups and periods, demonstrating the periodic nature of their properties more effectively than his predecessors.
14
An element has an atomic number of 17. What is its specific position in the modern periodic table?
Answer:
Period 3 group 17
Chlorine has an atomic number of 17. Its electronic configuration is 2, 8, 7. The presence of three electron shells places it in Period 3, and having seven valence electrons places it in Group 17 (the halogens).
15
Which of the following elements is not classified as a noble gas?
Answer:
Hydrogen
Noble gases are elements in Group 18 of the periodic table, characterized by full valence electron shells, making them chemically inert. Hydrogen is a non-metal in Group 1, which is highly reactive and does not share the inert properties of the noble gases.
16
How many elements are contained within the fourth period of the modern periodic table?
Answer:
18
The fourth period of the periodic table begins with potassium (atomic number 19) and ends with krypton (atomic number 36). It includes the s-block elements, the first row of transition metals (d-block), and the p-block elements, totaling 18 elements in the complete period.
17
How many elements are contained within the fourth and fifth periods of the periodic table?
Answer:
18 elements
The fourth and fifth periods of the periodic table are long periods. The fourth period involves filling the 4s, 3d, and 4p orbitals, while the fifth period involves filling the 5s, 4d, and 5p orbitals. Each of these periods accommodates exactly 18 elements, reflecting the capacity of the subshells being filled.
18
Which scientific principle states that the physical and chemical properties of elements are periodic functions of their atomic numbers?
Answer:
Modern periodic law
The Modern Periodic Law, formulated by Henry Moseley, establishes that the properties of elements are a periodic function of their atomic numbers. This corrected the earlier Mendeleev's law, which was based on atomic mass. By arranging elements by atomic number, the periodic table accurately reflects the electronic configuration and chemical behavior of elements.
19
What is the term used for the horizontal rows in Mendeleev's periodic table?
Answer:
period
In Mendeleev's periodic table, the horizontal rows were designated as periods. These rows organized elements based on increasing atomic mass, while the vertical columns were referred to as groups, grouping elements with similar chemical properties together.
20
Up to which element does Newlands' Law of Octaves hold true?
Answer:
Calcium
Newlands' Law of Octaves was based on the observation that every eighth element had properties similar to the first. However, this pattern only worked consistently for lighter elements up to calcium (atomic number 20). Beyond calcium, the introduction of transition metals disrupted the simple octet pattern, rendering the law less effective for heavier elements.