Can someone PLEASE help me with these questions?? Provide details as much as you
ID: 1001462 • Letter: C
Question
Can someone PLEASE help me with these questions?? Provide details as much as you can. Thanks!
Many metallic bonds tend to require the metal atoms to be packed close together (close packing). What is it about the metallic bonding that favors metals to be as closely packed as possible? Soft (easily worked) metals tend to be FCC types of metals what is it about FCC that make them easy to work into shapes? BCC structures are not so close packed and tend to be less ductile why do you think that is? HCP structures on the other hand, are close packed planes but have a tendency to be a bit more brittle rather than FCC why do you think that is? Why do you think a metal, for example, like tungsten, might crystallize as BCC when there are no close packed planes just close packed directionsExplanation / Answer
NOTE: Only four items were answered because that stated in the rules of Chegg.
a) For metals the atoms have low electronegativity’s; therefore the electrons are delocalized over all the atoms. We can think of the structure of a metal as an arrangement of positive atom cores in a sea of electrons. To maximize the bonding in a metal it makes sense to pack as many atoms around each other as possible, maximize the number of nearest neighbors (called the "coordination number") and minimize the volume.
In other words, atoms in metals lose electrons to form cations and delocalized electrons surround the ions. This form the metallic bonds (electrostatic interactions between the ions and the electron cloud) and hold the metallic solid together arranging like closely packed spheres.
b and c)
In order to understand this answer we need to first understand the concept of slip, slip plane and slip direction. Briefly stating slip is the movement of dislocation in the atomic level. This phenomena favors the plane which has the highest planar density and the direction which has highest linear density of the atom. Together the slip plane and slip direction are known as slip system. Now let’s come to the arrangement of atoms in FCC and BCC.FCC is a closed pack unit, hence the atoms per unit cubic cell is higher in comparison with BCC. If you look carefully you will find only 1 predominant family of plane in FCC which is {111} along with only 1 family of directions which is <110> and hence has a total amount of 12 slip system. Whereas in case of BCC which is not a closed pack system, does not has a predominant atomic density. Therefore total 3 family of planes acts as the slip planes and neither of them is a dominant and hence has a total of 48 slip system.
.Now when it comes to ductility, we need to deform the material and as a result of which the dislocation present inside them will also travel, but as mentioned earlier slip is the movement of dislocation and in FCC the atoms are closed pack and has a predominant slip system and hence the slip can travel easily inside it and the material can be deformed easily as a result it will be more ductile while in case of BCC the dislocation cannot travel with such an ease. And hence we can conclude that the FCC structure has more ductility than BCC.
d) HCP metals are more brittle than FCC and BCC metals because they have fewer active slip systems. FCC and BCC metals have many slip systems, which allows extensive plastic deformation (i.e. high ductility).