Metals make good electrical and thermal conductors because of this property. Groups are given names because of the similarity of the chemical properties of the elements within a group. Each element has a symbol associated with it. In fact, each isotope of each element has a symbol. The atomic symbol, X in the above diagram, is a shorthand for the name of the element and is uniquely defined by the atomic number and is therefore redundant.
Some elements have many stable isotopes, and some have famous unstable ones.
Remember, Chemistry is entirely determined by what the electrons are doing in an atom or molecule. The molecule, then, is the building block of a compound, just like the atom is a building block of the element. The molecule is the smallest portion of a compound that can be isolated and still retain the properties of the compuond. Structure, is first and foremost determined by the connectivity of the atoms in the molecule, i.e. what atoms have chemical bonds between them. Later, we will discuss in detail the lengths of the bonds and the angles between bonds to further describe the structure of molecules.