How to draw dot and cross diagram of covalent molecules

In this video, we will go through in detail, the drawing of 5 different covalent substances, namely hydrogen, oxygen, water, methane and carbon dioxide. From there, we will determine the structural formula of each substance.

Covalent bond

Covalent bond is formed when electrons are shared between non-metals. After bonding, each atom attains the noble gas electronic configuration. Do note that only the valence electrons in the outermost shell are involved. Atoms want to take part in chemical reaction because they want to achieve noble gas structure or noble gas configuration.

Atoms of noble gases are unreactive or stable.

Molecules

Elements and compounds with covalent bonds are called molecules. A molecule is a group of two or more atoms held together by covalent bonds.

Bond

When one pair of electrons is shared, a single bond is formed. For example, molecules like hydrogen, chlorine, fluorine, water, ammonia have single bonds between their atoms.
When two pairs of electrons are shared, a double bond is formed. For example, molecules like oxygen and carbon dioxide have double bonds between their atoms.

We can clearly see the number of bonds in a structural formula of the substance.

Knowing how to write accurate structural formula is particularly important when students deal with Organic Chemistry.