Question:

An ion has 18 electrons in the outermost shell, it is

Updated On: Jul 19, 2024
  • $Cu^+$
  • $Th^{4+}$
  • $Cs^+$
  • $K^+$
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The Correct Option is A

Solution and Explanation

The electronic configuration of Cu, Th, Cs and K are 
Cu(29) = 2, 8,18,1 
\(Cu^+\) = 2, 8,18 
Th(90) = 2, 8,18, 32,18,10, 2 
\(Th^{4+}\) = 2, 8,18, 32,18, 8 
Cs(55) = 2, 8,18,18, 8,1 
\(Cs^+\) = 2, 8,18,18, 8 
K(19) = 2, 8, 8,1 
\(K^+\) = 2, 8, 8 
Thus, \(Cu^+\) has 18 electrons in the outermost shell.

An ion with 18 electrons in the outermost shell can be one of several possibilities, depending on whether the ion has gained or lost electrons.

If the ion has gained electrons, it would have more than 18 electrons in the outermost shell, and would therefore have a negative charge. The most likely ion with 18 electrons in the outermost shell and a negative charge would be the chloride ion (Cl-), which has a total of 18 electrons in its outermost shell.

If the ion has lost electrons, it would have fewer than 18 electrons in the outermost shell, and would therefore have a positive charge. The most likely ion with 18 electrons in the outermost shell and a positive charge would be the argon ion (Ar+), which has 17 electrons in its outermost shell. If the argon atom were to lose one electron, it would have 18 electrons in the outermost shell and a net positive charge of +1.

However, it's important to note that the specific ion with 18 electrons in the outermost shell depends on the context of the problem and the specific elements involved.

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Concepts Used:

Structure of Atom

Atomic Structure:

The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons.

Dalton’s Atomic Theory

Dalton proposed that every matter is composed of atoms that are indivisible and indestructible. 

The following are the postulates of his theory:

  • Every matter is made up of atoms.
  • Atoms are indivisible.
  • Specific elements have only one type of atoms in them.
  • Each atom has its own constant mass that varies from element to element.
  • Atoms undergo rearrangement during a chemical reaction.
  • Atoms can neither be created nor be destroyed but can be transformed from one form to another.

Cons of Dalton’s Atomic Theory

  • The theory was unable to explain the existence of isotopes.
  • Nothing about the structure of atom was appropriately explained.
  • Later, the scientists discovered particles inside the atom that proved, the atoms are divisible.

​​Subatomic Particles

  1. Protons - are positively charged subatomic particles.
  2. Electron - are negatively  charged subatomic particles.
  3. Neutrons - are electrically neutral particles and carry no charge

Atomic Structure of Isotopes

Several atomic structures of an element can exist, which differ in the total number of nucleons.These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons.  For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium.