A water molecule forms when oxygen (o) and _______  atoms react and are held together by covalent bonds?
steam
nitrogen
carbon
hydrogen (h)
An example of a chemical compound is water. A water molecule forms when oxygen (O) and hydrogen (H) atoms react and are held together by covalent bonds. Like other compounds, water always has the same chemical composition: a 2:1 ratio of hydrogen atoms to oxygen atoms. This is expressed in the chemical formula H 2 O. A model of a water molecule is shown in Figure below .