The melting points of the alkali metals decrease from Li to Cs. In contrast, the melting points of the halogens increase from F2 to I2. (a) Using bonding principles, account for the decrease in the melting points of the alkali metals. (b) Using bonding principles, account for the decrease in the melting points of the halogens. (c) What is the expected trend in the melting points of the compounds LiF, NaCl, KBr, and CsI? Explain this trend using bonding principles.   Note: Please briefly explain all the questions listed above. Thank you.

Phosphorus (P) is present in a germanium (Ge) sample. Assume that one of its five valence electrons revolves in a Bohr orbit around each P+ ion in the Ge lattice. (a) If the effective mass of the electron is 0.17 me and the dielectric constant of Ge is 16, find the radius of the first Bohr orbit of the electron. (b) Ge has a band gap (Eg) of 0.65 eV. How does the ionization energy of the above electron comparing to Eg and kBT at room temperature?

Tellurium forms a compound with fluorine in which the tellurium ion has an oxidation number of +4. Write the chemical formula of the compound. Do not include the phase designation in the answer.

Which phosphorus nitride NP ,NP^+or NP^2- would be paramagnetic

Calculate the lattice enthalpies, ΔU (also called ΔHL), of the following group 1 fluoride compounds by using the Born–Mayer equation. The radius of Na is 102 pm and the radius of F– is 133 pm. The radius of Cs is 167 pm and the radius of F– is 133 pm.

1. Tantalum is rare, hard, blue-gray, lustrous transition metal that is highly corrosion-resistant. It has a density of 16.4 kg/L and a molecular weight of 180.948 g/mol. What is the (A) atomic radius in cm, (B) volume in cm^3 of Ta if it adopts the body centered cubic unit structure and (C) volume of unit cell

(1) Diamond and graphite are two minerals with identical chemical compositions, pure carbon (C). Diamond is the hardest of all minerals, and graphite is one of the softest. If their compositions are identical, why do they have such profound differences in physical properties? (2) silicon and oxygen together make up nearly 75 percent by weight of the Earth's crust. But silicate minerals make up more than 95 percent of the crust. Explain the apparent discrepancy. (3) If you were given a crystal of diamond and another of quartz, how would you tell which is diamond? (4) Would you expect minerais found on the Moon, Mars, or Venus to be different from those of the Earth's crust? Explain your answer. (5) Quartz is Si02. Why does no mineral exist with the composition Si03?

Tourmaline is the most colorful of all gemstones. It neutralizes negative forces and offers emotional stability. It is crystalline boron silicates compounded with metals such as Mg, Fe, Al, Na and Li.  The three most well-known minerals of tourmaline are: Elbaite                Na(LiAl2)Al6Si6O18(BO3)3(OH)4 Schorl                  Na(Fe3)Al6(BO3)3Si6O18(OH)4 Dravite                Na(Mg3)Al6(BO3)3Si6O18(OH)4   On a basis of 1000 kg of tourmaline rocks containing 25% Elbaite, 35% Schorl, 30% Dravite and 10% inerts, calculate the following: a)           kg Fe b)           total kg-atom O and kg-mol O2 in the three minerals c)           total number of Mg atoms in the rocks

Tourmaline is the most colorful of all gemstones. It neutralizes negative forces and offers emotional stability. It is crystalline boron silicates compounded with metals such as Mg, Fe, Al, Na and Li.  The three most well-known minerals of tourmaline are: Elbaite                Na(LiAl2)Al6Si6O18(BO3)3(OH)4 Schorl                  Na(Fe3)Al6(BO3)3Si6O18(OH)4 Dravite                Na(Mg3)Al6(BO3)3Si6O18(OH)4   On a basis of 1000 kg of tourmaline rocks containing 25% Elbaite, 35% Schorl, 30% Dravite and 10% inerts, calculate the following: a)           kg-mol Elbaite b)           % by wt BO3 in tourmaline rocks