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One of the most fundamental aspects of chemistry is understanding the atomic number. It plays a crucial role in defining the identity of an element. The atomic number refers to the number of protons found in the nucleus of an atom. Every element on the periodic table has a unique atomic number, distinguishing it from other elements.

For instance, hydrogen, the simplest element, has an atomic number of 1, which means each hydrogen atom has one proton. On the other hand, carbon has an atomic number of 6, signifying six protons in its nucleus. The atomic number isn't just a label; it also influences an atom's chemical properties and its place in the periodic table. When trying to comprehend why a pure sample of an element contains only one type of atom, the atomic number is a deciding factor.

Now let's talk about what is meant by a 'pure sample' in chemistry. A pure sample of a substance means that the material is composed of only one type of particle. In the case of an element, a pure sample would consist exclusively of atoms with the same atomic number. This level of purity ensures that the sample exhibits consistent properties and reactions.

A pure sample of gold, which has the atomic number 79, will only contain gold atoms. Contamination or mixing with other substances would lead to a sample that's no longer pure. In the laboratory or industrial processes, achieving a pure sample is critical for predictable outcomes in reactions and for creating materials with specific characteristics.

When it comes to differentiating between the types of atoms, it's important to recognize that each element's atoms are unique and identifiable by their atomic number. However, within a given element, there might be variations called isotopes, which have the same atomic number but different numbers of neutrons. Despite these differences, isotopes of an element are still considered the same type of atom.

Therefore, if you have a pure sample of an element, regardless of the presence of isotopes, you are dealing with just one type of atom. This is why a pure sample of any element—like our earlier examples of hydrogen or carbon—will offer a consistent and undivergent assembly of atoms related to that element. Understanding this concept is essential when predicting the composition of substances and the outcomes of chemical reactions.