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Define atomic radius (covalent radius) - Leaving Cert Chemistry - Question 2(b-d-e) - 2012
Question 2(b-d-e)
Define atomic radius (covalent radius). State and explain the trend in atomic radii (covalent radii) across the second period of the periodic table of the elements.... show full transcript
Worked Solution & Example Answer:Define atomic radius (covalent radius) - Leaving Cert Chemistry - Question 2(b-d-e) - 2012
Step 1
Step 2
State and explain the trend in atomic radii (covalent radii) across the second period of the periodic table
Answer
As we move across the second period of the periodic table, the atomic radius tends to decrease. This occurs due to an increase in effective nuclear charge, which is the net positive charge experienced by the electrons. The increase in nuclear charge (number of protons) pulls the electron cloud closer to the nucleus, resulting in a smaller atomic radius.
Step 3
Give one reason why electronegativity values exhibit a general increase across the second period
Answer
Electronegativity values increase across the second period primarily because of the increase in nuclear charge. As the number of protons increases while the shielding effect remains relatively constant, the attraction between the nucleus and the bonding electrons increases, resulting in higher electronegativity.
Step 4
i) State how the bonding in PH₃ differs from the bonding in the other three hydrides
Answer
In PH₃, the bonding is primarily covalent and exhibits virtually non-polar characteristics, while the other three hydrides (H₂O, NH₃, HCl) are polar due to a significant difference in electronegativity between the bonded atoms.
Step 5
Step 6
iii) Give one property that is affected by the presence of intermolecular hydrogen bonding in the hydride or hydrides you have identified
Answer
One property affected by intermolecular hydrogen bonding in H₂O and NH₃ is the boiling point. The presence of hydrogen bonding leads to higher boiling points compared to molecules without such bonding.
Step 7
iv) State the shape of the PH₃ molecule and explain using electron-pair repulsion theory how this shape arises
Answer
The shape of the PH₃ molecule is pyramidal. According to electron-pair repulsion theory, the lone pair of electrons on phosphorus repels the three bonding pairs, creating a trigonal pyramidal arrangement rather than a planar structure.
Step 8
e) Would you expect (i) the B-Cl bonds, (ii) the BCl₃ molecules, to be polar or non-polar? Justify your answers
Answer
i) The B-Cl bonds are considered polar due to the difference in electronegativity between boron and chlorine.
ii) The BCl₃ molecules are non-polar as the molecular geometry is trigonal planar, which allows the dipole moments of the B-Cl bonds to cancel each other out due to symmetry.