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KIMIA UMUM .... %100. 566. %4.56. ×. = x. 564. 56600. =x. 5. 1003. = 1003.5 566.5 437ppm. −. = ... Dr. Istadi, ST, MT, Buku Ajar Kimia Umum , 2009, Semarang :.
KIMIA UMUM Soal A (Kuliah Senin jam 08.00) Nama : Dimas Agung Pambudi NIM : L2C009096 1. Which of Dalton’s postulates about atoms are inconsistent with later observations? Do these inconsistencies mean that Dalton was wrong? Is Dalton’s model still useful? Explain clearl Answer :  Atom is a massive particle that can’t be divided into a smaller part, can’t be created, and can’t be destroyed. This postulate shows that atom is a smallest part of a substance, whereas in modern theory atom contains subatomic particles which are definitely smaller than atom. Those subatomic particles are proton, neutron, and electron. In education way, this postulate is very different with theory used modern now. People say Dalton’s Postulates were wrong but anyway it’s still used for atom development history. Dalton found what atom was and the next make it more perfect. And now people don’t use these postulate because the later observations show the more perfect one.

2. Given that the ions in LiF and in MgO are of similar size, which compound has stronger ionic bonding? Use Coulomb’s law in your explanations. Answer : Given Coulombs’ Law

Energy∼

charge1 × charge 2 distance

Comparing LiF and MgO from the charge, MgO has the bigger charge. LiF made from Li1+ + F1-, then MgO made from Mg2+ + O2-. The law shows that ion with bigger charge will product bigger energy too. Comparing the distance, because both have the similar size, so it can’t be defined by the distance. The smaller ion will product bigger energy. But in this case it has no smaller ion so the distance will be the same. The conclusion is, MgO is the compound has the stronger ionic bonding.

3. Rank the following photons in terms of decreasing energy: (a). IR (v=6.5E13 per second), (b). microwave (v=9.8×1011 per second), and (c). UV (v=8.0×1015 per second) Answer : 1. UV (v=8.0×1015 per second) 2. IR (v=6.5E13 per second) 3. Microwave (v=9.8×1011 per second)

4. Are the following quantum number combinations allowed? If not, show two ways to correct them: (a). n=2, l=0, ml=-1; (b). n=4, l=3, ml=-1; (c). n=3, l=1, ml=0; (d). n=5, l=2, ml=+3 Answer : (a). n=2, l=0, ml=-1 This quantum number combination isn’t allowed. It should be :  n=2, l=0, ml=0  n=2, l=1, ml=-1 (b). n=4, l=3, ml=-1 This quantum number combination is allowed. (c). n=3, l=1, ml=0 This quantum number combination is allowed. (d). n=5, l=2, ml=+3 This quantum number combination isn’t allowed. It should be :  n=5, l=2, ml=-2  n=5, l=3, ml=+3

5. Explain the difference of Hund’s rule, Pauli exclusion principle, and Aufbau principle. Give clear example if needed. Answer : • Hund’s Rule The orbital which has the same energy has to be filled up with halfparallel electron spin first, then its couple by the opposite. 2p2 (correct) 2p2 (wrong)



Pauli Exclusion Principle There is no two electrons has a same quantum number combination. H (Z=1) 1s1 He (Z=2) 1s2



Aufbau Principle : There is only one electron each substance on the lowest energy level.  For atom H (Z=1) n=1, l=0, ml=0, ms=+ 1 2  For atom He (Z=2) n=1, l=0, ml=0, ms= − 1 2 (First electron in He is similar with H, but the second electron in He has the opposite spin.)

6. Write the condensed ground-state electron configuration of these transition metal ions, and state which are paramagnetic: (a). V3+; (b). Cd2+; (c). Co3+; (d). Ag+ Answer : (a). V (Z=23) = 1s2 2s2 2p6 3s2 3p6 4s2 3d3 V3+ = 1s2 2s2 2p6 3s2 3p6 3d2 (b). Cd (Z=48)= 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4s2 4d10 Cd2+ = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10 (c). Co (Z=27) Co3+

= 1s2 2s2 2p6 3s2 3p6 4s2 3d7 = 1s2 2s2 2p6 3s2 3p6 3d6

(d). Ag (Z=47)= 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d9 Ag+ = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d9

7. The NaCl crystal structure consists of alternating Na+ and Cl- ions lying next to each other in three dimensions. If the Na+ radius is 56.4% of the Cl- radius and the distance between Na+ nuclei is 566 pm, what are the radius of the two ions? Answer : 566 56.4% = × 100% x 56600 x= 564

= 1003.5 1003.5 − 566.5 = 437ppm

8. Define bond energy using the H-Cl bond as an example. When this bond breaks, is energy absorbed or released? Is the accompanying ΔH value positive or negative? How do the magnitude and sign of this ΔH value relate to the value accompanying H-Cl bond formation? Answer : When a bond breaks, that bond absorbs energy, because it’s influenced by dipole-dipole force which is happened between the molecules. ΔH is influenced by dipole, if the dipole is big so it will boil on a high temperature. Then that heat is used as an energy to against dipole-dipole force between molecule H and Cl, so ΔH will be positive because it needs energy from that heat.

DAFTAR PUSTAKA Dr. Istadi, ST, MT, Buku Ajar Kimia Umum , 2009, Semarang : Universitas Diponegoro W. Keenan, Charles, Donald C. Kleinfelter, Jesse H. Wood, Ilmu Kimia Untuk Universitas Edisi Keenam , 1980, Jakarta : Erlangga www.wikipedia.org