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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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A 1.25 g gas sample occupies 663 ml at 25∘ c and 1.00 atm. what is the molar mass of the gas?
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Using ideal gas equation,  

P\times V=n\times R\times T

Here,  

P denotes pressure  

V denotes volume  

n denotes number of moles of gas  

R denotes gas constant  

T denotes temperature  

The values at STP will be:  

P=1 atm  

T=25 C+273 K =298.15K

V=663 ml=0.663L

R=0.0821 atm L mol ⁻¹

Mass of gas given=1.25 g g

Molar mass of gas given=?

Number of moles of gas, n= \frac{Given mass of the gas}{Molar mass of the gas}

Number of moles of gas, n= \frac{1.25}{Molar mass of the gas}

Putting all the values in the above equation,

1\times 0.663=\frac{1.25}{Molar mass of the gas}\times 0.0821\times 298.15

Molar mass of the gas=46.15

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