Take simple note of "Atoms are the building blocks of matter, and they can combine to make new substances called compounds. Compounds can be classified as ionic or covalent, depending on how the atoms are bonded together. In a covalent bond, two atoms share electron pairs, while in an ionic bond, electrons are fully transferred between two atoms. When atoms combine to form compounds, they create a distinct group of atoms held together by chemical bonds. These bonds are similar to the electrostatic attraction that holds the structure of an atom together."