Problem: Write the electron configuration for the following ions, and determine which have noble-gas configurations:a. Cd2+b. P3- c. Zr4+ d. Ru3+e. As3-f. Ag+

FREE Expert Solution

We're asked to write the electron configuration for the following ions, and determine which have noble-gas configurations.


Recall that when an atom forms an ion it either gains or loses electrons:


  • positive charge means valence electrons are removed or lost
  • negative charge means electrons are added or gained


The valence electrons are found in the highest numbered orbital or higher energy orbital in a subshell.


  • For main group(Group A) elements, the last or outermost orbital gains or loses the electron
    • found in s, and p orbitals
  • For transition metals (also known as Group B)the last s orbital loses an electron before the d orbitals.
    • found in d orbital


For this problem, we need to do these steps:

Step 1: Determine # of electrons from atomic number using Periodic Table

Step 2: Write ground-state electron configuration 

Ground-state means that the element is in its lowest energy form (not in excited state). 

Step 3: Write electron configuration of each ion

Step 4:  Compare with nearest noble gas to determine whether it has a noble gas configuration


Recall that electron configurations are written from lower energy to higher energy orbital.


The following periodic table shows the orbitals in order of increasing energy levels: s < p < d < f:



Recall that the distribution of electrons for each atomic orbital are:


s         _               1 orbital  can hold a maximum of 2 electrons

       _ _ _            3 orbitals → can hold a maximum of 6 electrons

d       _ _ _ _ _       5 orbitals → can hold a maximum of 10 electrons

f      _ _ _ _ _ _ _   7 orbitals → can hold a maximum of 14 electrons

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Problem Details

Write the electron configuration for the following ions, and determine which have noble-gas configurations:

a. Cd2+
b. P3- 
c. Zr4+ 
d. Ru3+
e. As3-
f. Ag+

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