Certain pieces of jewelry are not completely silver. They are silver-plated on the outside and another metal on the inside, like steel. Silver-plated jewelry is less expensive than their full silver counterparts. Silver tarnishes, or breaks down, when it comes in contact with hydrogen sulfide, H2S, which is found in the air and in some foods. Explain, in terms of electrons, why the compound that tarnishes silver is covalent.