Question

Which of the following are covalent binary compounds?
(A) $B{{F}_{3}}$
(B) KBr
(C) $Ca{{I}_{2}}$
(D) $Al{{F}_{3}}$

Answer 1

Hint: Think about the differences between ionic and covalent compounds. Define a covalent compound. Find out what binary compounds are. Take a look at each of the given options. First categorize them into ionic or covalent compounds and then choose the correct option.

Complete step by step solution:
- An ionic compound is a compound in which there is a presence of ionic bonds. An ionic bond is formed by complete electron transfer by the atoms to form ions. An ionic bond formation involves gain or loss of electrons by the atoms to form ions which get negative or positive charges and are held together to form molecules.
- A covalent bond is formed when two or more atoms taking part in formation of a molecule form a bond by sharing valence electrons and attaining stability. The bonds formed by sharing of electrons are covalent bonds and such compounds are called covalent compounds.
- A binary covalent compound is a covalent compound which has two different elements present in it. For example, $AlC{{l}_{3}}$. Here two elements aluminium and chlorine are present.
- Now, let’s take a look at the options.
(A) $B{{F}_{3}}$ - Boron trifluoride is a covalent compound as it forms three covalent bonds with three fluorine atoms. This compound has only two elements present, boron and fluorine and so, it is a binary covalent compound.
(B) KBr – Potassium bromide is an ionic compound. We know that group I and group II elements generally form ionic compounds due to their high electropositivity and large size. Potassium loses one electron to bromine which gains one electron to form bromide ion.
(C) $Ca{{I}_{2}}$- Calcium iodide is an ionic compound. Calcium is again a group II element which is electropositive and will donate its electrons to two iodine atoms which gain one electron each to form iodide.
(D) $Al{{F}_{3}}$ - Aluminium fluoride is a covalent compound. Just like boron trifluoride, aluminium forms three covalent bonds with fluorine. This compound is a binary covalent compound.
- Therefore, $B{{F}_{3}}$ and $Al{{F}_{3}}$ are binary covalent compounds.

- Therefore, the answer is option (A) and (D).

Note: Remember that group I and group II elements generally form ionic bonds due to their large size and high electropositive character. The ability to form more covalent compounds is seen in p-block elements among themselves and other block elements also form covalent compounds only.