Q. 4.76 - An Introduction to General, Organic, and Biological Chemistry

Question

a. How many neutrons are in $K-41$?

b. Write the electron arrangement for potassium.

c. Which is the larger atom. $K$or $Cs$?

d. Which is the smallest atom, $K, As,$ or $Br$?

e. If John's potato field has an area of $34.5$ hectares. How many pounds of fertilizer does John need to use?

Step-by-Step Solution

Answer

(a) The no. of neutrons are $22$

(b) The electron arrangement for potassium is $\left[Ar\right]4s^1$

(c) The larger atom is $Cs$

(d) The smallest atom is $Br$

(e) Amount of fertilizer John needs to use is $12930.1 lb$

Part (a) Step 1: Given information

We need to find the no. of neutrons in $K-41$

Part (a) Step 2: Simplify

We know that,

Mass no. is equal to the sum of no. of protons and no. of neutrons.

And Atomic no. of potassium is $19$

Also, Atomic no. is equal to no. of protons. Hence no. of protons are, $19$

Here, mass no. is $41$

Therefore, 

No. of neutrons are equal to the difference of mass no. and no. of protons i.e. $41-19=22$

Part (b) Step 1: Given information

We need to find the electron arrangement for potassium

Part (b) Step 2: Explanation

We know that,

Atomic no. of potassium is $19$

And atomic no. is equal to no. of electrons

Hence no. of electrons are $19$

Therefore electron arrangement of potassium is,

  $\left[Ar\right]4s^1$

Where $Ar$ is argon having atomic no. $18$

Part (c) Step 1: Given information

We need to find the larger atom among $K,Cs$

Part (c) Step 2: Explanation

We know that,

$K$ and $Cs$ lie in the same group but different periods.

And as we move top to bottom in a group atomic size increases 

Since, $K$ is at the top as compared to $Cs$

Therefore, The larger atom is  $Cs$

Part (d) Step 1: Given information

We need to find the smallest atom among $K, As, Br$

Part (d) Step 2: Explanation

We know that,

$K, As, Br$ lie in the same period but in different groups.

And Size of the atom decreases as we move left to right in the period.

Since $Br$ is in the right as compared to both the other atoms

Therefore, The smallest atom is $Br$

Part (e) Step 1: Given information

We are given that area of John's potato field is $34.5$hectares.

Part (e) Step 2: Simplify

We know that,

John needs to apply $170 kg$ fertilizer per hectare.

As the field is $34.5$ hectares

Therefore, fertilizer needed is, 

   $$\begin{gathered} 34.5\times 170 \\ =5865 kg \\ =5865\times 2.2 lb \\ =12930.1 lb \end{gathered}$$