Question

Write the complete symbol for the atoms with given atomic and mass no, \[Z{\text{ }} = {\text{ }}18{\text{ }}A{\text{ }} = {\text{ }}40\] and \[A{\text{ }} = {\text{ }}39\] (Z \[ = \] Atomic no and A \[ = \] mass)

Answer 1

Hint: For a given atom, you can write its symbols as \[_Z^AX\] . Here, X is the symbol of the element, Z is its atomic number and X is its mass number.

Complete answer:
Atomic number is equal to the number of protons. It is also equal to the number of electrons. The mass number is equal to the sum of the number of protons and neutrons. Protons and neutrons are present in the nucleus whereas electrons are present in extra nuclear space. You can obtain the number of electrons present in a neutral atom from its atomic number. You can obtain the number of protons present in an atom from its atomic number. You can obtain the number of neutrons by subtracting the atomic number from the mass number.
In a neutral atom, the number of protons is equal to the number of electrons. Protons and electrons have unit positive and unit negative charges. If the number of protons is greater than the number of electrons, then cation is formed. If the number of electrons is greater than the number of protons then anion is formed.
The element with Z \[ = \] 18 has an atomic number of 18. Argon is the inert gas having an atomic number of 18. The complete symbol for Argon with Z \[ = \] 18, A \[ = \] 40 is \[_{18}^{40}{\text{Ar}}\] . Here, the atomic number is 18 and the mass number is 40.

The complete symbol for Argon with Z \[ = \] 18, A \[ = \] 39 is \[_{18}^{39}{\text{Ar}}\] . Here, the atomic number is 18 and the mass number is 39.

Additional Information: The number of valence electrons present in argon is 8. So argon has completed its octet and is chemically inert. In the modern periodic table, inert gases are present on the rightmost part. Argon is present in the third period.

Note: \[_{18}^{39}{\text{Ar}}\] and \[_{18}^{40}{\text{Ar}}\] represents a pair of isotopes. They have the same atomic number of 18 but they differ in the mass numbers. The mass numbers of \[_{18}^{39}{\text{Ar}}\] and \[_{18}^{40}{\text{Ar}}\] are 39 and 40 respectively.