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lakkis [162]
3 years ago
5

How many core electrons are in a ground state atom of selenium?

Chemistry
1 answer:
Harman [31]3 years ago
3 0
Electrons in an atom can be classified as core electrons and valence electrons. Valence electrons are those electrons which are present in valence shell and participates in bond formation. While, Core electrons are all remaining electrons which are not present in valence shell, hence not take part in bonding.

Atomic number of Selenium (Se) is 34 hence it has 34 electrons with following electronic configuration;

                          1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁴

From electronic configuration it is found that the valence shell is 4, and the number of electrons present in valence shell are 6. So, 

             Core Electrons  =  Total Electrons - Valence Electrons

             Core Electrons  =  34 - 6

             Core Electrons  =  28

Result:
          There are 28 core electrons in Selenium.
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6 Na + 1 Fe₂O₃ → 3 Na₂O + 6 Fe

<h3>Explanation</h3>

Method One: Refer to electron transfers.

Oxidation states:

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  • Fe: from +3 to 0; gains three electrons.

Each mole of Fe₂O₃ contains two Fe atoms and will gain 2 × 3 = 6 electrons during the reaction. It takes 6 moles of Na to supply all those electrons.

6 Na + 1 Fe₂O₃ → ? Na₂O + ? Fe

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6 Na + 1 Fe₂O₃ → 3 Na₂O + 2 Fe

Method Two: Atoms conserve.

Fe₂O₃ has the largest number of atoms among one mole of all four species in this reaction. Assume <em>one</em> as its coefficient.

? Na + <em>1</em> Fe₂O₃ → ? Na₂O + ? Fe

There are two moles of Fe atoms and three moles of O atoms in each mol of Fe₂O₃. One mole of Fe₂O₃ contains two moles of Fe and three moles of O. There are one mole of O atom in every mole of Na₂O. Three moles of O will go to three moles of Na₂O.

? Na + <em>1</em> Fe₂O₃ → <em>3</em> Na₂O + <em>2</em> Fe

Each mole of Na₂O contains two moles of Na. Three moles of Na₂O will contain six moles of Na.

<em>6</em> Na + <em>1</em> Fe₂O₃ → <em>3</em> Na₂O + <em>2</em> Fe

Simplify the coefficients. All coefficients in this equation are now full number and relatively prime. Hence the equation is balanced.

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