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What was the initial understanding of the atom, as reflected in the Greek word 'a-tomio'?
The word ‘atom’ has been derived from the Greek word ‘a-tomio’ which means ‘uncut-able’ or ‘non-divisible’. (NCERT, Chapter: STRUCTURE_OF_ATOM)
Before Dalton, the ideas about the existence of atoms were primarily:
The existence of atoms has been proposed since the time of early Indian and Greek philosophers (400 B.C.). According to them, the continued subdivisions of matter would ultimately yield atoms which would not be further divisible. These earlier ideas were mere speculations and there was no way to test them experimentally. (NCERT, Chapter: STRUCTURE_OF_ATOM)
Which of the following aspects of atomic structure could NOT be explained by Dalton's atomic theory, but required later scientific advancements?
Dalton's atomic theory regarded the atom as the ultimate particle of matter and did not include any internal structure. The detailed understanding of the electronic structure of atoms, including the distribution and relative energies of electrons, developed with later atomic models like Bohr's and the quantum mechanical model. The question 'why two or more atoms combine to form molecules, why some elements are metals while others are non-metals... find simple explanation from the electronic configuration. These questions have no answer in the Daltonian model of atom.' (NCERT, Chapter: STRUCTURE_OF_ATOM)
John Dalton's Atomic Theory, proposed in 1808, was significant for:
The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school teacher in 1808. (NCERT, Chapter: STRUCTURE_OF_ATOM)
Which of the following statements correctly describes the polarity of the carbon-halogen (C-X) bond in an alkyl halide?
According to the NCERT text, 'Halogen atoms are more electronegative than carbon, therefore, carbon-halogen bond of alkyl halide is polarised; the carbon atom bears a partial positive charge whereas the halogen atom bears a partial negative charge.'
Arrange the following C-X bonds in increasing order of their bond length: C-F, C-Cl, C-Br, C-I.
The NCERT text states, 'As we go down the group in the periodic table, the size of halogen atom increases. Fluorine atom is the smallest and iodine atom is the largest. Consequently the carbon-halogen bond length also increases from C—F to C—I.' This implies that C-F has the shortest bond length and C-I has the longest bond length.
What is the primary reason for the partial double bond character of the C-Cl bond in haloarenes?
The context mentions, 'C— Cl bond acquires a partial double bond character due to resonance' where 'lone pair of electrons on halogen atom are in conjugation with p -electrons of the ring'.
Compare the reactivity of haloalkanes and haloarenes towards nucleophilic substitution reactions based on the nature of the C-X bond.
The NCERT text states, 'C— Cl bond acquires a partial double bond character due to resonance. As a result, the bond cleavage in haloarene is difficult than haloalkane and therefore, they are less reactive towards nucleophilic substitution reaction.' Additionally, it mentions, 'C— Cl bond length in haloalkane is 177pm while in haloarene is 169 pm. Since it is difficult to break a shorter bond than a longer bond, therefore, haloarenes are less reactive than haloalkanes towards nucleophilic substitution reaction.'
Which of the following refers to the hybridisation of the carbon atom to which the halogen atom is bonded in a haloalkane?
The NCERT text defines haloalkanes as compounds containing 'halogen atom(s) attached to the sp$^3$ hybridised carbon atom of an alkyl group'.
In a vinylic halide, the halogen atom is attached to a carbon atom with what hybridization?
Vinylic halides are defined as compounds 'in which the halogen atom is bonded to a sp$^2$-hybridised carbon atom of a carbon-carbon double bond (C = C)'.
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