NH4Br has a face-centered cubic unit cell in which the Br- anions occupy corners and face centers, while the cations fit into the hole between adjacent anions. What is the radius of Br- if the ionic radius of NH4 is 138.3 pm and the density of NH4Br is 2.429 g/cm3

Ionic radius of the bromide ion is 227.9 pm.

Explanation:

Number of atom in FCC unit cell = Z = 4

Density of ammonium bromide =

Edge length of cubic unit cell= a= ?

Molar mass of ammonium bromide = 98 g/mol

Formula used :  

where,

= density

Z = number of atom in unit cell

M = atomic mass

= Avogadro's number  

a = edge length of unit cell

On substituting all the given values , we will get the value of 'a'

Ionic radius of bromide ion = r

To calculate the edge length, we use the relation between the radius and edge length for FCC lattice:

Putting values in above equation, we get:

Ionic radius of the bromide ion is 227.9 pm.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.