An element 'X', having atomic number 19, is represented by electronic configuration  K L M 2 8 8 Which of the following statements for this configuration is true ?

Option 2 : It is the configuration of cation of element 'X'.

The correct answer is It is the configuration of cation of element 'X'.

Concept:

Electronic configuration:

• It can be defined as the distribution of electrons around the nucleus in different energy levels (shells).
• It was suggested by Bohr and Bury.

Rules for writing the electronic configuration of an atom:​

• The maximum number of electrons present in a shell is given by the formula 2n2, where ‘n’ is the orbit number or energy level index, 1,2,3, and so on.
• Hence, the maximum number of electrons in different shells is as follows:
  • The First orbit or K-shell will be = 2 × 12 = 2,
  • The second orbit or L-shell will be = 2 × 22 = 8,
  • The Third orbit or M-shell will be = 2 × 32 = 18,
  • The fourth orbit or N-shell will be= 2 × 42= 32, and so on.
• The maximum number of electrons that can be accommodated in the outermost orbit is 8.
• Electrons are not accommodated in a given shell unless the inner shells are filled. That is, the shells are filled in a step-wise manner.

Ions: 

• An atom or group of atoms that bears one or more positive or negative electrical charges, is called an ion.
• Cations: Positively charged ions formed by losing electrons. 
• Anions: Negatively charged ions are formed by gaining electrons.

​Atomic number:

• It is equal to the number of protons or electrons in an electrically neutral atom.
• Thus, Atomic Number = No. of protons of an atom

​Explanation:

• The element 'X', having atomic number 19, is represented by electronic configuration: ​

• No. of electrons = 2 + 8 + 8 = 18 
• The atomic number is 19. 
• So, the number of protons = 19
• Here, the number of protons is more than the number of electrons. 
• The element X must have lost one electron to form a cation. 

So, the given electronic configuration is of cation of element X.