Periodic Table — Set 3
Chemistry · आवर्त सारणी · Questions 21–30 of 40
Which of these is a characteristic of covalent compounds?
Correct Answer: C. Formed between two non-metals
Covalent bonds typically form between non-metal atoms that share electrons. These compounds generally have lower melting points than ionic compounds. They are often poor conductors of electricity in any state.
What is the term for the distance between the nuclei of two bonded atoms at their minimum potential energy?
Correct Answer: C. Bond length
Bond length is the average distance between the centers of two bonded atoms. It is determined by the balance between the attraction of nuclei for electrons and the repulsion between nuclei. Generally, triple bonds are shorter than double or single bonds.
Which molecule has a bent or 'V' shape geometry?
Correct Answer: C. $H_2O$
The correct answer is '$H_2O$'. Water has a bent shape because of the two lone pairs of electrons on the oxygen atom. These lone pairs exert more repulsion than bonding pairs, pushing the hydrogen atoms closer together. The resulting bond angle is approximately 104.5 degrees.
The property of being drawn into thin wires is known as?
Correct Answer: D. Ductility
Ductility is a physical property of metals enabled by their unique metallic bonding. The 'sea of electrons' allows metal atoms to slide past each other without breaking the bond. This makes metals highly useful for electrical wiring.
Which compound is formed by electrovalent bonding?
Correct Answer: D. Calcium Oxide
Calcium Oxide ($CaO$) is formed by the transfer of electrons from Calcium to Oxygen, which is an electrovalent (ionic) bond. Calcium becomes a $Ca^{2+}$ cation and Oxygen becomes an $O^{2-}$ anion. This compound is commonly known as quicklime.
How many lone pairs of electrons are present on the central nitrogen atom in an ammonia ($NH_3$) molecule?
Correct Answer: A. 1
Nitrogen has five valence electrons, three of which are used for bonding with hydrogen. The remaining two electrons form one lone pair on the nitrogen atom. This lone pair causes the molecule to have a trigonal pyramidal shape.
Which theory explains the geometry of molecules based on the repulsion between electron pairs?
Correct Answer: C. VSEPR Theory
VSEPR stands for Valence Shell Electron Pair Repulsion theory. It assumes that electron pairs around a central atom will position themselves as far apart as possible. This theory is very effective at predicting the 3D shapes of simple molecules.
In which state do ionic compounds conduct electricity?
Correct Answer: D. Molten or dissolved in water
In the molten or dissolved state, the ions are free to move and carry an electric current. In a solid, ions are locked in a rigid lattice and cannot move. This transition from insulator to conductor is a hallmark of ionic substances.
What is the maximum number of electrons that can be accommodated in the valence shell of a Period 1 element?
Correct Answer: A. 2
Period 1 elements like Hydrogen and Helium only have the 1s orbital. This orbital can hold a maximum of two electrons. Therefore, Helium is stable with only two electrons, which is called a duet.
Which type of bond is found in a molecule of $Cl_2$?
Correct Answer: B. Non-polar covalent
A chlorine molecule consists of two identical atoms sharing a pair of electrons equally. Since both atoms have the same electronegativity, the bond is non-polar covalent. This bond is formed by the overlap of p-orbitals.