The electrons are not shared equally creating a molecule

The answer is a polar molecule.

When atoms form a covalent bond they share electrons in order to achieve the stable configuration of noble gases.
However, some atoms have a higher electronegativity, the ability to attract electrons. When atoms with different levels of electronegativity form a covalent bond the atom with higher electronegativity attracts the electrons more, creating polarity within the molecule.

The mass has escaped into a gas which you can not see so the law stays true.