12.5 notes

figure 12.24 answer

Ionic substances cleave because the nearest neighbor interactions switch from attractive to repulsive if the atoms slide so that ions of like charge(cation-cation, anion-anion) touch each other. metals dont cleave because the atoms are attracted to all other atoms in the crystal through metallic bonding

when the cation and anion are very similar in size what happens?

a large coordination number is favored

nacl(rock salt structure) and ZnS(zinc blende) is based on face centered cubic lattice

anions sit on the lattice points that lie on the corners and faces of unit cell

as the atoms get smaller (atomic radii decreases) what happens? ionic radius or ion gets smaller

cation and anion coordination number decrease and cation radius decreases ionic radius of ion changes very little

motif plus crystal lattice equals what?

crystal structure

what happens as the relative size of cation gets smaller/

eventually it is no longer possible to maintain the cation-anion contacts and simultaneously keep the anions from touching eachother when this occurs then the coordination number drops and the next structure become more favorable.

as the cation/anion ratio goes down , there are what?

fewer cations to surround each anion and so the anion coordination number must decrease.

what happen as charges increase and size decrease?

interactions between cations and anions increase

why do metallic bonds and ionic bonds have different properties?

ionic and metallic bonds both have high melting points but the valence electrons in ionic bonds are confined to the anions rather than delocalized so ionic compounds are typically insulators ionic bonds are poor conductors and are brittle (due to repulsive interactions between ions of like charge)

the cesium chloride structure is based on what?

primitive cubic lattice . anions sit on the corners of the unit cell , and a cation sits at the center of each cell. (there is no lattice point inside a primitive unit cell)

how are metallic solids and ionic solids similar?

tend to adopt structures with symmetric , close packed arrangements of atoms.

the strength of an ionic solid depends on what?

the charges and size of ion

what happens when stress is applied to an ionic solid?

the planes of atoms before stress was arranged with cations next to anions , shift so that the alignment becomes cation-cation, anion-anion, .the resulting repulsive interaction causes the planes to split away from each other and leads to the formation of certain gemstones such as ruby