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
What is the typical valence electron configuration for metallic elements?
Answer:
Metals have 1 to 4 valence electrons in their outer shells
Metals are characterized by their tendency to lose electrons to form positive ions. Typically, metallic elements possess between 1 and 4 valence electrons in their outermost shell, which allows them to achieve stability through electron donation rather than sharing or gaining.
2
Which of the following properties is inversely related to the electronegativity of an element?
Answer:
Metallic properties
Electronegativity is the measure of an atom's ability to attract shared electrons in a bond. Metallic character is defined by the tendency of an element to lose electrons. Since high electronegativity implies a strong hold on electrons (non-metallic behavior) and low electronegativity implies a weak hold (metallic behavior), metallic properties are inversely related to electronegativity.
3
How does the metallic character of elements change as the atomic number increases across a period?
Answer:
Metallic character decreases
As you move from left to right across a period, the effective nuclear charge increases, which pulls the valence electrons closer to the nucleus. This makes it harder for atoms to lose electrons, thereby decreasing their metallic character and increasing their non-metallic character.
4
What significant scientific contribution is attributed to the Russian chemist Dmitry Mendeleev?
Answer:
Periodic table of chemical elements
Dmitry Mendeleev is widely recognized for formulating the Periodic Law and creating the first version of the Periodic Table of Elements. He organized elements based on their atomic weights and chemical properties, famously leaving gaps for elements that had not yet been discovered at the time.
5
An element has an electronic configuration of 2, 8, 3. To which group does this element belong?
Answer:
13
The electronic configuration 2, 8, 3 indicates that the element has three valence electrons. For elements in the p-block, the group number is calculated as 10 + number of valence electrons. Therefore, 10 + 3 = 13. This element is Aluminum, which is located in Group 13.
6
How do metallic character and electropositivity change across a period (left to right) and down a group (top to bottom)?
Answer:
Electrically positive / metallic character, - decreases / increases - increases
Metallic character and electropositivity decrease across a period from left to right because the effective nuclear charge increases, making it harder to lose electrons. Conversely, they increase down a group because the valence electrons are further from the nucleus due to additional electron shells, making them easier to lose.
7
Which of the following statements accurately describes the structure of the modern periodic table?
Answer:
It consists of 18 vertical columns, which are called groups
The modern periodic table is organized into 18 vertical columns known as groups and 7 horizontal rows known as periods. Elements within the same group share similar chemical properties due to their identical valence electron configurations.
8
When moving from left to right across a period in the periodic table, which property remains constant?
Answer:
shells
In the periodic table, elements in the same period share the same number of principal energy levels, or electron shells. As you move from left to right across a period, electrons are added to the same outer shell, while the number of protons and electrons increases by one for each successive element.
9
Which scientific law states that the properties of elements are periodic functions of their atomic masses?
Answer:
Mendeleev's Periodic Law
Mendeleev's Periodic Law states that the physical and chemical properties of elements are a periodic function of their atomic weights (masses). This was the foundational principle used to organize the first widely accepted periodic table, predating the modern law based on atomic number.
10
Which set of elements was predicted by Mendeleev and later found a place in his periodic table?
Answer:
Sc, Ga and Ge
Mendeleev predicted the existence and properties of several elements. Specifically, Scandium (Sc), Gallium (Ga), and Germanium (Ge) were the elements that filled the gaps he left for 'eka-boron', 'eka-aluminium', and 'eka-silicon', respectively, providing strong evidence for his periodic classification system.