Structures of solids

Question 1

Metallic bonding

Answer 1

Free electrons- electrons are loosely held to the ions, the bond is non-directional.

Question 2

Ionic bonding

Answer 2

Electron transfer- exchange electrons between metallic and non-metallic atoms- directional

Question 3

Covalent

Answer 3

Electron sharing- atoms to share the valence electrons to satisfy their partially filled electronic orbits (directional and strong)

Question 4

Hydrogen bond

Answer 4

H covalently bonded to an electronegative atom. Strong as H is small.

Question 5

Van de Waals bond

Answer 5

Forces arise when electrons are not distributed equally among ions which form dipoles. The dipole-dipole interactions do not give rise to directional bonds and the force is much weaker than the hydrogen bonds.

Question 6

Substitutional defects

Answer 6

In materials science- alloying if intentional, impurities if not. In semiconductors- impurities.

Question 7

Line defects

Answer 7

Line defects are created when an extra plane of atoms is displaced or dislocated out of its regular space registry. They tend to lower the mechanical strength of the material dramatically as it takes less energy to move or deform a whole plane of atoms one atomic distance at a time than to try to do it all at once. But introducing a lot of dislocations can increase the strength because they become entangled with another.

Question 8

Planar defects

Answer 8

Occur at grain boundaries- individual grains have different crystal orientation to its neighbours

Question 9

Effects of planar defects

Answer 9

1) creates areas of mismatch along the boundaries with the atoms at the boundaries having higher energy
2) Grain boundaries tend to be less dense- more diffusion occurs at the grain boundary
3) A material will be stronger if made up of many fine grains than large ones as the increased number of boundaries interfere with the movement of atoms during deformation