Which elements can form diatomic molecules joined by a single covalent bond?

Hydrogen and halogens.

Explanation:

There are seven types diatomic molecules are present in natural state: Hydrogen, chlorine, fluorine, nitrogen, bromine, iodine, and oxygen.

Hydrogen is the first element which have one electron and needs only one electron to fill its valence shell and form 2 hydrogen single bond to form H2.

The halogens, chlorine, fluorine, bromine, and iodine they all contain seven valence electrons. They all need one more electron so, they are sharing their one electron to fill its valence shell, and get Cl2, F2, Br2 and I2 (all single bonds)

Oxygen contains six valence electrons, each oxygen molecule needs 2 more electrons, and they contain 2 unpaired electrons. So, they share both electrons and form double bond.

Nitrogen contains five valence electrons. Each nitrogen atom required 3 more electrons and contains 3 unpaired electrons. The 2 atoms shares all 3 with each other molecule and this form a triple bond.

So, only Hydrogen and halogens form diatomic molecules with the help of single bond

Halogen elements and H, O, N.

Explanation:

All halogen elements can form covalent bonds with each other to form a diatomic molecule. You can also add nonmetals, H, O and N.

All halogens have a configuration that differs from that of noble gases in an electron, so these elements tend to form negative species (anions) or form simple covalent bonds.

The Halogen are Cl, F, Br, I, As.

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.