Define electronegativity.
Account for the decreasing trend in electronegativity values down Group 17 of the periodic table.
Predict the shape of a molecule of
(i)... show full transcript
Worked Solution & Example Answer:Define electronegativity - Leaving Cert Chemistry - Question b - 2022
Step 1
Define electronegativity.
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Answer
Electronegativity is defined as a measure of the ability of an atom to attract shared pairs of electrons in a covalent bond. It is a relative value that indicates how strongly an atom can pull electrons towards itself.
Step 2
Account for the decreasing trend in electronegativity values down Group 17 of the periodic table.
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Answer
As we move down Group 17 (the halogens) in the periodic table, the electronegativity values decrease due to several factors:
Atomic Radius: The atomic radius increases as more electron shells are added. This increases the distance between the nucleus and the valence electrons, reducing the nucleus's pull on the bonding electrons.
Electron Shielding: There is an increase in the number of inner shell electrons that shield the nucleus from attracting the bonding electrons. This shielding effect weakens the nucleus's ability to attract electrons.
Nuclear Charge Influence: Although the nuclear charge increases with additional protons, the effect of increased shielding and distance outweighs this, leading to a decrease in electronegativity.
Step 3
Predict the shape of a molecule of (i) silicon tetrachloride (SiCl₄), a colourless liquid.
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Answer
The shape of silicon tetrachloride (SiCl₄) is tetrahedral due to the presence of four bond pairs around the silicon atom, which are arranged to minimize electron pair repulsion.
Step 4
Predict the shape of a molecule of (ii) sulfur dichloride (SCl₂), a cherry-red liquid.
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Answer
The shape of sulfur dichloride (SCl₂) is V-shaped (bent/angular) due to the presence of two bond pairs and lone pairs that repel each other, which leads to a bent molecular geometry.
Step 5
Predict the shape of a molecule of (iii) phosphorus trichloride (PCl₃), another colourless liquid.
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Answer
The shape of phosphorus trichloride (PCl₃) is trigonal pyramidal. This arises from three bond pairs around the phosphorus atom and one lone pair, resulting in a pyramid-like structure.
Step 6
Which one of these three compounds (iv) is non-polar?
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Answer
Silicon tetrachloride (SiCl₄) is the non-polar compound due to its symmetrical tetrahedral shape, which allows the bond dipoles to cancel out.
Step 7
Which one of these three compounds (v) has bonds that have the least degree of polarity?
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Answer
Silicon tetrachloride (SiCl₄) has bonds that exhibit the least degree of polarity among these compounds due to the comparable electronegativities of silicon and chlorine, leading to a more non-polar character.
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