Question

How are atoms arranged in pure metals?

Answer 1

Hint: The basic arrangement of atoms in a pure metal at its very core involves nuclei of atoms being arranged in a certain arrangement and are surrounded by a sea of electrons, this fixated nuclei are sometimes called kernels and are approximated to have a static nature in terms of arrangement, however the electrons are dynamic in nature and tend to move continuously around the nuclei or kernels which is why we cannot specify whether an electron belongs to a specific nuclei or not.

Complete answer:
Knowing the above basics we should not indulge on how the nuclei of atoms are arranged in a metal, An atom could be now approximated to be present wherever it’s nuclei is now present. Basic of the simple nature of atoms they are approximated to be identical perfect spheres which crystallize to give one of the four basic structures namely:
a-Simple Cubic$\left( {SC} \right)$
b-Body-centered Cubic$\left( {BCC} \right)$
b-Hexagonal closed packed$\left( {HCP} \right)$
d-Cubic close packing$\left( {CCP} \right)$
To study their nature we study the nature of a unit cell present in the structure of the metal, as this helps us in understanding all the basics of the structure in the most efficient way:
a-Simple cubic$\left( {SC} \right)$, in this type of rearrangement the smallest unit of the structure comprises $8$atoms coming along $8$ corners of a cube with every corner touching all the nearby corners. It has a packing efficiency of around $52\% $.
b-Body-centered Cubic$\left( {BCC} \right)$, as the name suggests it comprises a unit cell where $8$ atoms are at $8$ corners of a cube and $1$ atom is at body centre. It has a packing efficiency of $68\% $.
c-Hexagonal close packing involves a unit cell that comprises $2$hexagons formed by $6$atoms each meeting along a particular axis. It has an efficiency of $74\% $.
d-Cubic close packing involves a unit cell that has $8$ atoms at $8$ corners of a cube alongside$6$atoms at each of the face centers. It has a packing efficiency of $74\% $ and is one of the most commonly found metal structures alongside$HCP$.

Note: Depending on the type of metal atom and its surrounding conditions a metal could have one or more possible structures however in general we find only one which is their most stable one in nature. Also, we need to keep in mind that when we say that atom is present at the corners of say a cube it is not the atom but rather its nuclei which at any instant is surrounded by a sea of electrons that do not belong specifically to any particular nuclei.