19 pts - how do you determine if something is isoelectronic? which of the following is isoelectronic- o2, f-, ne, na se2-, br-, kr, rb+ i-, xe, cs, ba2+

Isoelectronic means equal number of electrons.

The method to determine if elements are sioelectronic is:

1) Determine the atomic number of the element (search the element in the periodic table).

2) The atomic number is equal to the number of protons (always, by definition).

3) If the atom is neutral, the number of electrons is equal to the number of protons.

3) If the species is not neutral then:

     - if it is a negative ion, add as many electrons as the magnitude of the charge of the ion

    - if iit is a positive ion, subtract as many electrons as the magnitude of the charge of the ion.

4) One by one

species          atomic number              charge          number of electrons
                      number of protons

O₂,                    8                                     0                 8 (each atom)
F-                     9                                      -1               9 + 1 = 10    
Ne                  10                                      0                10
Na                  11                                       0               11

So, in that group only F- and Ne are isoelectronic, each with 10 electrons

Se2-               34                                      -2                34 + 2 = 36
Br-                  35                                      -1                35 + 1 = 36
Kr                   36                                       0                36
Rb+                37                                      +1               37 - 1 = 36

So, in that group all are isoelectronic.
   
I-                     53                                     -1                 53 + 1 = 54
Xe                   54                                     0                  54
Cs                   55                                     0                  55  
Ba2+               56                                    +2                 55 - 2 = 53

So, in that group only I- and Xe are isoelectronic.

A.