Chapter 5, Problem 25E

Interpretation Introduction

Interpretation:

The name of element, nuclear symbol, atomic number, mass number, number of protons, electrons and neutrons in the table are to be stated.

Concept introduction:

An atom is the smallest unit of matter. This smallest unit exhibits properties of chemical element. An atom consists of three sub-atomic particles such as electrons, protons and neutrons. Electrons are negatively charged, protons are positively charged and neutrons are neutral in nature.

Answer to Problem 25E

The table on completion is shown below.

Name of Element	Nuclear Symbol	Atomic Number	Mass Number	Protons	Neutrons	Electrons
Scandium	$\text{S}\text{c}$	$\text{21}$	$45$	$\text{21}$	$\text{24}$	$\text{21}$
Germanium	$\text{G}\text{e}$	$32$	$76$	$32$	$44$	$32$
Tin	$\text{S}\text{n}$	$\text{50}$	$\text{122}$	$\text{50}$	$\text{72}$	$\text{50}$
Chlorine	$\text{C}\text{l}$	$\text{17}$	$\text{37}$	$\text{17}$	$20$	$\text{17}$
Sodium	$\text{N}\text{a}$	$\text{11}$	$23$	$\text{11}$	$\text{12}$	$\text{11}$

Explanation of Solution

Atomic number is the number of protons. In a neutral atom, the number of protons is equal to the number of electrons. Mass number of a neutral atom is equal to the sum of number of neutrons and number of protons.

An atom is represented as shown below.

$\text{X}$

Where,

• $\text{X}$ is the symbol of element.

• $\text{Z}$ is the atomic number.

• $\text{A}$ is the mass number.

Calculation of number of neutrons is shown below.

$\text{A}=n_p+n_n$ …(1)

Where,

• $n_p$ is the number or protons.

• $n_{}$

n is the number of neutrons.

The table to be filled is given below.

Name of Element	Nuclear Symbol	Atomic Number	Mass Number	Protons	Neutrons	Electrons
					$\text{24}$	$\text{21}$
	$\text{G}\text{e}$
			$\text{122}$		$\text{72}$
			$\text{37}$			$\text{17}$
		$\text{11}$			$\text{12}$

For first row, the number of electrons is equal to number of protons and atomic number that is $21$.

Substitute the value of $n_n$ as $24$ and $n_p$ as $21$ in the equation (1) as shown below.

$\begin{array}{rll}\text{A}& =& 21+24\\ & =& 45\end{array}$

Therefore, mass number is $45$. The element is identified as Scandium with nuclear symbol as $\text{S}\text{c}$.

For second row, the nuclear symbol is $\text{G}\text{e}$. The element is identified as Germanium.

On comparison with the above stated atomic representation, atomic number of $\text{G}\text{e}$ is $32$. Therefore, the number of protons and electrons are $32,32$ respectively. The mass number is $76$.

Substitute the value of $\text{A}$ as $76$ and $n_p$ as $32$ in the equation (1) as shown below.

$\begin{array}{rll}76& =& 32+n_n\\ n_n& =& 76-32\\ & =& 44\end{array}$

Therefore, the number of neutrons is $44$.

For third row, The mass number is $122$ and number of neutrons is $72$. Substitute the value of $\text{A}$ as $122$ and $n_n$ as $72$ in the equation (1) as shown below.

$\begin{array}{rll}122& =& n_p+72\\ n_p& =& 122-72\\ & =& 50\end{array}$

Therefore, the atomic number is $50$, that is same as number of electrons and number of protons. The element is identified as Tin with nuclear symbol $\text{S}\text{n}$

For fourth row, the mass number is $37$ and number of electrons is $17$. Therefore, the number of protons and atomic number both are equal to $17$. For calculation of number of neutrons, substitute value of $\text{A}$ as $37$ and $n_p$ as $17$ in equation (1) as shown below.

$\begin{array}{rll}37& =& 17+n_n\\ n_n& =& 37-17\\ & =& 20\end{array}$

The element is identified as Chlorine with nuclear symbol $\text{C}\text{l}$.

For fifth row, the atomic number is $11$. Therefore, number of protons and number of electrons both are equal to $11$. The number of neutrons is $12$. Substitute the value of $n_n$ as $12$ and $n_p$ as $11$ in the equation (1) as shown below.

$\begin{array}{rll}\text{A}& =& 12+11\\ & =& 23\end{array}$

Therefore, the mass number is $23$. The element is identified as Sodium with nuclear symbol $\text{N}\text{a}$.

Conclusion

The table on completion for the required values on the basis of atomic representation has been rightfully stated above.