Periodic Table — Set 4
Chemistry · आवर्त सारणी · Questions 31–40 of 40
Which of the following is true for a covalent bond?
Correct Answer: D. It involves sharing of electrons
Covalent bonds are formed by the mutual sharing of one or more pairs of electrons. This typically occurs between atoms with high electronegativities that don't want to lose electrons. Most organic molecules are held together by covalent bonds.
The bond formed between an element of Group 1 and Group 17 is usually?
Correct Answer: C. Ionic
Group 1 metals lose one electron easily, while Group 17 non-metals gain one electron easily. This large difference in attraction leads to the formation of an ionic bond. Table salt ($NaCl$) is the most famous example of this combination.
Which molecule has a triple bond?
Correct Answer: A. $N_2$
Nitrogen atoms share three pairs of electrons to fulfill the octet rule. This triple bond is one of the strongest chemical bonds known. It requires a large amount of energy to break, contributing to nitrogen's stability.
What is the formal charge on the Carbon atom in the $CO_2$ molecule?
Correct Answer: A. 0
Formal charge is calculated by subtracting assigned electrons from valence electrons. In $CO_2$, the carbon atom shares all four of its valence electrons, resulting in a formal charge of zero. A formal charge of zero usually indicates a stable electronic structure.
Which of the following describes the polarity of a water molecule?
Correct Answer: A. Polar
Water is a polar molecule because oxygen is more electronegative than hydrogen and the molecule is asymmetrical. This polarity allows water to act as a 'universal solvent' for many substances. It also leads to the formation of hydrogen bonds between water molecules.
Which type of hybridization is found in the $BeCl_2$ molecule?
Correct Answer: B. $sp$
Beryllium in $BeCl_2$ forms two single bonds and has no lone pairs, leading to $sp$ hybridization. This results in a linear molecular geometry with a 180-degree bond angle. It is an example of an electron-deficient molecule.
Which intermolecular force is present in all molecules, both polar and non-polar?
Correct Answer: C. London dispersion force
London dispersion forces arise from temporary shifts in electron density. They are universal and occur between all atoms and molecules. While individually weak, they can become significant in large, heavy atoms.
Which of the following atoms does not typically follow the octet rule?
Correct Answer: C. Boron
Boron often forms compounds like $BF_3$ where it only has six valence electrons. This is known as an incomplete octet or being electron-deficient. Such compounds are often very reactive and act as Lewis acids.
What is the name of the process where an atom loses an electron?
Correct Answer: A. Oxidation
Oxidation is defined as the loss of electrons by an atom or ion. This term originated from reactions involving oxygen but now applies to any electron loss. The mnemonic 'LEO says GER' (Loss of Electrons is Oxidation) is helpful to remember this.
A bond between two atoms with an electronegativity difference greater than 1.7 is generally considered?
Correct Answer: B. Ionic
A high electronegativity difference indicates that one atom has a much stronger pull on electrons than the other. This usually results in a complete electron transfer, forming an ionic bond. This 1.7 threshold is a common guideline used in chemistry textbooks.