   Chapter 7, Problem 27PS

Chapter
Section
Textbook Problem

Arrange the following elements in order of increasing size: Al, B, C, K. and Na. (Try doing it without looking at Figure 7.5; then check yourself by looking up the necessary atomic radii.)

Interpretation Introduction

Interpretation:

The given elements have to be arranged in increasing order of size.

Concept Introduction:

Atomic radius: The concept explain chemical element is a measured of the size of its atoms, in other words to measure the distance from the center of the nucleus to the boundary of the surrounding cloud of number of electrons.

Increase and decrease electronegativity: The less vacancy electrons an atoms has the least it will gain of electrons. Moreover the electron affinity decrease down the groups and from right to left across the periods on the periodic table, the reason is electrons are placed in a higher energy level far from the nucleus thus a decrease from its pull.

Electron attachment enthalpy: ΔEAH is defined as the enthalpy change occurring when a gaseous atom adds an electron forming a gaseous anion.

A(g)+e-A-(g)----ElectronattachmententhalpyEAH

Explanation

According to periodicity, the elements atomic size will decrease along the period and increases down the group.

• Let us consider fallowing S-block elements

The potassium (K) atomic radius greater than sodium (Na) due to the addition of shells and (K) atomic number (Z=19), sodium atomic number (Z=11), here potassium has a larger atomic radius than sodium (Figure:1). So the attraction between the nucleus and the valence electrons decreases as you move down the group.

Figure: 1

Hence the increasing size of atoms K>Na

• Let us consider fallowing P-block elements

The Aluminum (Al) atomic radius greater than Boron (B) and Carbon (C) atoms because addition of electrons on the new shell

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