Question

How the following compounds are formed from the constituent atoms.
A.Sodium Chloride
B.Potassium Fluoride
C.Water
D.Hydrogen Chloride

Answer 1

Different elements form compounds with other elements in order to complete their octet and attain more stability. The aim is to have a completely filled last shell in the electronic configuration.

Complete step by step answer:
-Sodium Chloride:
We know that sodium has one electron in its valence shell and need to lose one electron to attain noble gas-like configuration while chlorine is one electron short of completing its octet. When both the atoms interact, the sodium atom loses one electron and chlorine gains one. This makes sodium positively and chlorine negatively charged.
Since opposite charges attract each other, we can conclude the sodium cation attracts chloride anion thus forming an ionic bond. The chemical formula for sodium chloride is $NaCl$.
-Potassium Fluoride
The chemical formula of potassium fluoride is $KF$.
We know potassium has one electron in its valence shell and tends to lose it to attain a complete octet and fluorine has 7 electrons thus, tends to accept an electron. Potassium fluoride is formed when potassium loses one electron to form a cation while fluoride takes up an electron to form an anion. As a result, an ionic bond is formed.
-Water
Hydrogen has one electron in its valence shell and needs one more to completely fill its $1s$ orbital. Oxygen on the other hand, requires two electrons to complete its octet. So, oxygen shares a single electron with two hydrogen atoms forming two covalent bonds.
-Hydrogen Chloride
We know that hydrogen has a single atom in its valence shell and is one electron short from a noble gas like configuration. Similar is the case with chlorine which has 7 electrons in its valence shell.
Thus, both the atoms share an electron with each other forming a covalent bond.

Note:
When ionic compounds are formed, the formula of the compounds can be determined by cross multiplying their valencies. For covalent compounds, lewis structures are used to determine the sharing of electrons and thus, their chemical formula.