Properties and characteristics of covalent compounds

In covalent or molecular compounds, unlike ionic ones, the atoms are held together by covalent bonds . Covalent bonds take place when atoms share electrons. The number of covalent compounds is quite high, so there can be quite a few exceptions when it comes to generalizing a theory regarding the properties of said compounds.

Compounds can be ionic or covalent. In covalent compounds, atoms form covalent bonds consisting of shared pairs of electrons between two adjacent atomic nuclei.

However, in an ionic compound, electrons are completely transferred from one atom to another, leaving the parent atom with more or fewer electrons depending on whether it acquires or loses them. Therefore, a cation can be formed , which is a positively charged element because it has more protons than electrons (it has lost one or more electrons) or an anion , a negatively charged atom because it has more electrons than protons (it has gained one or more electrons). The most common example of ionic compounds is NaCl, sodium chloride, or common salt.

Covalent Bonds and Molecules

A covalent bond is formed when two atoms share pairs of electrons . In a covalent bond, the stability of the bond is established thanks to the shared electrostatic attraction between two positively charged atomic nuclei and the negatively charged electrons in the vicinity of those nuclei.

When atoms combine to form covalent bonds, the result is a molecule. We can therefore say that a molecule is the simplest unit of a covalent compound.

Chemical formulas, also called molecular formulas, are the simplest way to represent molecules. It is a chemical formula, we use the symbols of the elements of the periodic table to indicate which elements are present, and the subscripts indicate how many atoms of each element exist in the molecule.

For example, a single molecule of ammonia contains one nitrogen and three hydrogen atoms: NH ₃ . Similarly, a hydrazine molecule contains two nitrogen and four hydrogen atoms: N ₂ H ₄ .

Sometimes we can see molecules like acetic acid written as C ₂ H ₄ O ₂ , but it can also be written as CH ₃ COOH. The second formula is written to help find out the structure of the molecule, while the first is to find out the number of atoms of each element.

CARACTERISTICS of the covalents compounds

• Low melting and boiling points . A relatively small amount of energy is required to overcome the weak attractions between covalent molecules, so these compounds melt and boil at much lower temperatures than metallic and ionic compounds. In fact, many of the covalent compounds are liquids or gases at room temperature.
• Low enthalpies of fusion and vaporization , smaller than those of ionic compounds.
• Soft or brittle solid forms , due to their weak intermolecular forces.
• Null electrical and thermal conductivity of covalent molecular compounds, contrary to what happens with ionic compounds, which conduct electricity well when melted, and so do metallic solids.

Sources

• General Chemistry Online: FAQ: Solids: What properties distinguish molecular compounds from other materials? . (2021). Retrieved 10 April 2021, from https://cutt.ly/uc2AT50

• Molecules and compounds overview | Atomic structure (article) | Khan Academy. (2021). Retrieved 10 April 2021, from https://cutt.ly/vc2OCll