Barium crystallizes in a body-centered cubic system with atoms at all lattice points and an edge length of 5.02 angstroms. Calculate its density in g/cm3.

Answer : The density is,

Explanation :

Formula used :  

.............(1)

where,

= density  = ?

Z = number of atom in unit cell (for BCC = 2)

M = atomic mass  of barium = 137.3 g/mole

= Avogadro's number =  

a = edge length of unit cell  =

Conversion used :

Now put all the values in above formula (1), we get

Thus, the density is,

the seeing the electronic configuration we can say that the element is fluorine.

fluorine is the most electronegative element in the periodic table.

but by only seeing the configuration we cannot say about its reactivity because we don't know if its configuration after excitation or by addition of electrons.

but if not then, it is the lightest halogen and exists as a highly toxic pale yellow diatomic gas at standard conditions. as the most electronegative element, it is extremely reactive: almost all other elements, including some noble gases, form compounds with fluorine.