The basic building blocks of matter are called atoms. An atom is the smallest particle of a element that exhibits the unique properties of that substance. An atom's identity as an element is determined by the number of protons in its nucleus (the atomic number.) The subatomic particles, protons, neutrons, and electrons, are not unique to the atom they make up - an electron from a carbon atom is indistinguishable from that of a silicon atom.
Atoms combine with other atoms to form compounds, which are held together by chemical bonds. There are over 10 million known compounds made of various combinations of around 90 elements. (There are 92 naturally occurring elements, but some aren't part of any compounds.)
During chemical reactions bonds between atoms are broken and new bonds are formed making new compounds. Even though the atoms are rearranged they remain intact as representatives of their respective elements.