Question

How would you rank these bonds from most ionic to most covalent in character?
 Br-F, Ca-F. K-F, F-F, Cl-F?

Answer 1

Hint:To answer this question we should know what ionic and covalent molecules are. We should also know electronegativity. We will compare the electronegativity difference of the bonded atoms. Higher the electronegativity difference more will be the ionic character.

Complete answer:
A bond between two atoms forms by two electrons, one from each atom. The tendency of an atom to attract the shared pairs of electrons is known as electronegativity.
If an atom of a bond has high electronegativity and another has very low electronegativity then one atom will attract the bonded electrons more towards it. So, one atom will get a negative charge and another will get a positive charge. The charged atoms are known as ions and the bond between ions known as an ionic bond.
If the bonded atoms have the same electronegativity or nearly the same then both attract the bonded electrons pair similarly. The bond is known as a covalent bond.
If the electronegativity difference is greater than $2$ , the bond will be ionic.
If the electronegativity difference is less than $0.5$ , the bond will be covalent.
The electronegativity of Br is $2.9$ and F is $3.9$ so, the electronegativity difference is $1.0$.
The electronegativity of Ca is $1.0$ and F is $3.9$ so, the electronegativity difference is $2.9$.
The electronegativity of K is $0.8$ and F is $3.9$ so, the electronegativity difference is $3.1$.
The electronegativity of F is $3.9$ so, the electronegativity difference is $0$.
The electronegativity of Cl is $3.1$ and F is $3.9$ so, the electronegativity difference is $0.8$.
According to electronegativity difference the K-F is most ionic and F-F is covalent. The order of decreasing ionic or increasing covalent character is as follows:
K-F > Ca-F > Br-F > Cl-F > F-F
Therefore, the order of most ionic to most covalent character is K-F > Ca-F > Br-F > Cl-F > F-F.

Note:If we don’t know the electronegativity of every atom just by knowing the general trend we can also compare the ionic and covalent character. Electronegativity increases from left to right in the periodic table, so alkali metals are least electronegative and halides are most electronegative. As K-F, K is alkali metal and F is halide so, there will be the highest electronegativity difference so, K-F will be the most ionic. In a group on going down, the electronegativity decreases. So, we take Br-F and Cl-F, we know the fluorine comes first in the group after that chlorine and then bromine. There will be the highest electronegativity difference if we take topmost and down most elements.