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What is the difference between diatomic molecules and elements?
Also, If oxygen is element of a single atom, then what makes it a diatomic element? But, then I read that a single oxygen atom can bind with another element to form a compound, but it's a diatomic element with two atoms.
Please can someone enlighten some clarity on this subject. Also, it would help to see some examples to see the differences and context of how these diatomic molecules and elements interact.
From the IUPAC Gold book ( https://goldbook.iupac.org/terms/view/C01022 )
Chemical Element
(1) A species of atoms; all atoms with the same number of protons in the atomic nucleus.
(2) A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. Sometimes this concept is called the elementary substance as distinct from the chemical element as defined under ($1$), but mostly the term chemical element is used for both concepts.
The form an element usually has is distinct from the fact it is an element
The key for a substance to be described as an element is that it contains only one type of atom. But that leaves a variety of possible structures even for one element.
Some elements–noble gases–consist of isolated atoms, all others consist of molecules or structures containing multiple atoms of the element. Oxygen mostly appears as a diatomic gas under normal conditions but sometimes appears a a triatomic gas (ozone). Some elements are usually seen as more complex molecules. Sulfur has a variety of allotropes (that's what different structures of pure elements are called) many containing rings of 8 sulfur atoms but others are known. Carbon has an interesting range of structures. One is a ball-shaped molecule of 60 carbons, graphite is a soft compound consisting of planes of hexagons weakly held together, diamond is a network of interlinked carbon tetrahedra and is very strong.
Elements, in other words, can be found as a variety of structures and many single elements can be seen with more than one structure. Some usually appear as single atoms, some as small molecules, some as large molecules and some as network solids. Some elements can be seen in multiple forms. All those forms are still elements. Don't confuse the form with the fact the substance is an element.
An element is the smallest entity that has it's own characteristics in Chemistry. Any two different elements differ fundamentally in respect to the number of protons in their nuclei. An element is always of single atom. It's the characteristic properties of that element that would decide in what form or kind of molecule it will be found in nature.
Diatomic element is a kind of molecule in which two atoms of the same or different elements have combined chemically to form a molecule. If we restrict ourselves to the context of elements, then diatomic element is one among various allotropes of the element.
Oxygen is found in nature as diatomic and triatomic (ozone). The reason we don't find monoatomic oxygen often around is that an atom of oxygen is highly reactive. You may have heard of nascent oxygen but it exist for very short time in some chemical reactions. O, O2 and O3 are different allotropes of the same element oxygen. Besides these, there are some other allotropes of oxygen that are listed in the given reference.
