Dalton s Postulates about atoms are inconsistent with later observations :

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Leonard Bryan Taylor
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1 Name : Netya Shoma Siwi Pertiwi NIM : 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 clearly! Dalton s Postulates about atoms are inconsistent with later observations : a. According to Dalton, atom is matter or solid particles that can t be divided, but in its development, we know that the atom can be divided into subatomic particles (proton, electron, and neutron) b. According to Dalton, atoms of an element can t be changed into atoms of other elements, in its development, the change can t be done with chemical reactions, but can be changed by nuclear reactions The inconsistency not mean that Dalton s Postulate is wrong. Postulate Dalton became material for the development of atomic theory by other researchers. Until now, there are some of Dalton's postulates are still used, for example, the formation of compounds derived from the atomic elements that are chemically joined with a certain ratio and the uniqueness of the atomic properties of elements. 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. Ionic strength depends on attraction or repulsion that can be explained with Coulomb's law. Energy of attraction or repulsion between two particles is comparable to the multiplication of the two charges and inversely comparable to the distance between the two particle.

2 Ions in LiF and MgO have the same size, this indicates that the distance between two particles in compound is same. So, things that affect the ionic strength is the charge of each compound. Ions in LiF has a smaller energy than MgO because MgO ions (Mg2 + and O2-) have bigger charge than the LiF (Li +1, and F-1) 3. Rank the following photons in terms of decreasing energy: (a). IR (v=6.5x per second), (b). microwave (v= per second), and (c). UV (v= per second) a. UV E=hv E=(6.626 x J.s) (8 x /s) E= x J b. IR E=hv E=(6.626 x J.s) (6.5 x /s) E= x J c. Microwave E=hv E=(6.626 x J.s) (9.8 x /s) E= x J So, the rank is UV>IR>Microwave 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

3 a. Not allowed n = 2 2 l = 0 s ml = -1 only there ml 0 0 b. Allowed n = 4 4 l = 3 f ml = c. Allowed n = 3 3 l = 1 p ml = d. Not allowed n = 5 5 l = 2 d ml = +3 highest ml just until Explain the difference of Hund s rule, Pauli exclusion principle, and Aufbau principle. Give clear example if needed. a. Hund s Rule orbital which have the same energy, first, half-filled electron with parallel electron spin, then its partner with opposite spin.

4 Example : O (Z=8) 1s 2 2s 2 2p 4 not b. Pauli exclusion principle there are not 2 electrons in the same atom can have the same 4 quantum numbers Example : Helium (He, Z=2) dan Hidrogen (H, Z=1) [He] first electron in ground state has the same combination of quantum numbers like Hydrogen atoms, but the second electron from Helium is different. Meaning, any electrons must have a unique identity. For the helium atom, the second electrons placed the same orbital but has a different orientation, so that: n = 1 l = 0 ml = 0 and ms =- 1 / 2 c. Aufbau Principle There are maximum two electrons that can be filled into the orbital with order of increasing orbital energy: the lowest-energy orbital is filled before electrons are placed into higher-energy orbitals. Example : O (Z=8) 1s 2 2s 2 2p 4 6. Write the condensed ground-state electron configuration of these transition metal ions, and state which are paramagnetic: (a). V 3+ ; (b). Cd 2+ ; (c). Co 3+ ; (d). Ag + Elements with unpaired electrons show paramagnetic properties (influenced by external magnetic field) a. V (Z= 23) [Ar] 4s 2 3d 3 V 3+ 4s 3d 4s 3d

5 b. Cd (Z= 48) [Kr] 2 10 Cd 2+ c. Co (Z =27) [Ar] 4s 2 3d 7 4s Co 3+ 4s 3d d. Ag (Z=47) ) [Kr] 1 10 Ag+ Paramagnetic : V 3+, Co 3+ 3d 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 radii of the two ions? 56,4 % = 566 Distance of Cl- and its nucleus 566 : 56,4 x 100 = 1003,5 The radii of the two ions is : 1003, = 1569,5 ppm 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?

6 H +δ CL -δ 2,1 3 H = +436 kj/mol To removed the bond, it give energy from outside.

TUGAS KIMIA UMUM KELOMPOK A (kuliah Senin jam 08.00)

Nama : Hary Permadi NIM : L2C0 09 092 TUGAS KIMIA UMUM KELOMPOK A (kuliah Senin jam 08.00) 1. Which of Dalton s postulates about atoms are inconsistent with later observations? Do these inconsistencies