I was able to complete the rest of the packet except the majority of section 4 (

Question

I was able to complete the rest of the packet except the majority of section 4 (questions 1, 2, and 3) and the last question.

CHEMISTRY /L.3w.S,4 Page 2 2. (2 pts) The yellow compound, BF has been found to have a structure like that of diborane. There are two BBB three-center bonds in this structure. bonds are the normal two-center variety structure below All other Draw this IV. Answer the following: 1. (2 pts) Silicon and carbon are both in Group IVA of the periodic table, yet the chemistry of silicon resembles that f boron ) which is in Group IIIAmore than it does that of carbon. Explain why this is so. 2. (3 pts) List the three most common raw materials used to make glass 3. (2 pts) Explain why borazine has been called "inorganic benzene."

Explanation / Answer

IV.1. Si and B are neither in the same group or same period, yet they have quite unexpected similarity in their properties. This is due to their diagonal placement in the periodic table, called as 'diagonal relationship'. This unusual relationship occurs because going from left to right across a period and from up to down across a group in the periodic table have opposite effects. For example, the size of the atoms decreases while going rightward a period of the periodic table, and the size of the atoms increases on moving down a group. Similarly, the elements become progressively more covalent on moving rightward across a period, more electronegative and less basic, whereas the elements become more ionic, more basic and less electronegative on moving down the group. Thus, on both crossing the period by one element and descending a group and , the changes sort of nullify each other, and elements with similar properties which have similar chemistry are often observed, in terms of the atomic size, electronegativity etc. of the diagonal members are similar.

2. 3 main ingredients to make glass: Silica sand (SiO2), soda ash (Na2CO3) and limestone (CaCO3).

3. Borazine is an inorganic compound which has a similar molecular formula [(BH)3(NH)3] as benzene (C6H6). It is isoelectronic and isostructural with benzene, having alternate BH and NH bonds to form a 6-membered cyclic ring system. Hence, it is called 'inorganic benzene'.

5. The balanced equation of B5H9 combustion in air is as follows:

2 B5H9 + 12 O2 --> 5 B2O3 + 9 H2O

So, the heat of combustion for 2 moles of B5H9 = 5 * Hf (B2O3) + 9 * Hf (H2O) - 2 * Hf(B5H9) - 12 * Hf(O2)

= [5 * (-1254.5) + 9 * (-241.818) - 2 * 54 - 0] kJ [since O2 is an element, so enthalpy of formation of O2 = 0]

= -8556.862 kJ

Hence, heat of combustion per mole of B5H9 = -8556.862 kJ/2 mol = -4278.43 kJ/mol

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