This is an oxygen atom, it is part of the covalent bond that makes up water (H20)
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This are both Hydrogen atoms that make up water in the covalent bone
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Oxygen and hydrogen are both unstable atoms, for reference a stable atom has 8 valence electrons. Oxygen's electron configuration is 2-6 and Hydrogen's E.C is 1 . meaning that oxygen needs two valence electrons to be stable and Hydrogen needs seven.
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This compound is made in a way were Hydrogen and oxygen both share and both get what they want, Oxygen shares its 6 plus the two hydrogen shares makes it stable for all 3 atoms in this compound, and since they are all non-metal is is a covalent compound