How do you answer these questions about the element selenium?

Question

Answer the following questions about the element selenium.

a) Samples of natural selenium contain six stable isotopes. In terms of atomic structure, explain what these isotopes have in common and how they differ.

b) Write the complete electron configuration (i.e. 1s2…) for a selenium atom in the ground state. Indicate the number of unpaired electrons in the ground-state atom and how it may react in a chemical reaction. Explain your reasoning.

c) In terms of atomic structure, explain why the first ionization energy of selenium is less than that of bromine, and greater than that of tellurium.

d) Selenium reacts with fluorine to form selenium tetrafluoride. Draw the complete Lewis electron-dot structure for SeF4 and sketch the molecular structure. Indicate whether the molecule is polar or nonpolar, and justify your answer.

Answer 1

a) Samples of natural selenium contain six stable isotopes.

these isotopes have the same number of proton & electrons in each atom

they differ in the number of neutrons in each atom, the atomic mass, & their nuclear stability

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b) Write the complete electron configuration (i.e. 1s2…) for a selenium atom in the ground state.  Electron configuration 1S2, 2S2, 2P6, 3s2, 3p6, 4s2, 3d10, 4p4

Indicate the number of unpaired electrons in the ground-state atom

it has 2 unpaired electrons in the 4P orbital

and how it may react in a chemical reaction. in a chemical reaction it is likely to take 2 electrons & become Se-2 or likely to do 2 covalent bond with other atom,

Explain your reasoning. this will allow it to have that "inert gas configuration of 8 electrons in its valence shell

it is also likely to lose all 6 electrons in its valence shell & become a +6, or fewer electrons & become  +4 or a +2 just as sulfur does above it in the same group

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c) In terms of atomic structure, explain why the first ionization energy of selenium is less than that of bromine,

which means that it is easier for it to lose electrons than it is for Br, this is because Br has the same atomic radius (115 pm) as does Se, but Br  more protons to hold its electrons from being taken, & itso  has a stronger pull for its own electrons

and greater than that of tellurium. Se has a strong hold on its electrons, because it is a smaller atom than Te, with Te's valence electrons further out the strength with which they are held falls off  by the square with distance. Te has a radius of 140 pm compared to Br's of 115 pm

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d) Selenium reacts with fluorine to form selenium tetrafluoride. Draw the complete Lewis electron-dot structure for SeF4 and sketch the molecular structure. Indicate whether the molecule is polar or nonpolar, and justify your answer.

view the structurde @

http://en.wikipedia.org/wiki/Selenium_te...

the orange is Se , the yellows are F's, replace each line bond between the Se & the F's with 2 electrons, & place 3 extra pairs of electrons around each fluorine, now look @ the last link to position a non bonded pair of electrons on the equator of Selenium

also look @ http://www.chemthes.com/entity_datapage....

to see that the 4 fluorine do not cancel each other out in the center... you have one non bonded pair of electrons 120 degrees away from 2 Fluorines with 4 pairs of electrons each... yes it is polar

the molecular structure is abbreviated AX4E1 "Seesaw " & can be viewed again @ http://en.wikipedia.org/wiki/VSEPR  

where they show SF4