Yes, it is possible for something to be made of only one type of atom or particle. Such substances are known as pure elements or elemental substances. An element is a type of substance in which all the atoms have the same atomic number, representing the number of protons in the nucleus of each atom.
Elements are the building blocks of matter, and each element is uniquely characterized by its atomic number. For example, the element hydrogen (H) consists of only hydrogen atoms, each containing a single proton in its nucleus. Similarly, the element carbon (C) consists of carbon atoms, each containing six protons.
There are currently 118 known elements on the periodic table, and each element has its own distinct properties. Some elements, like hydrogen and helium, are composed of individual atoms. Others, like oxygen and nitrogen, exist as diatomic molecules, where two atoms of the same element are chemically bonded together. Still, all the atoms in these elements are of the same type.
In addition to atoms, particles like electrons, protons, and neutrons can also exist as independent entities. However, they are not considered elements since elements are defined based on the properties and characteristics of the atoms they compose.
So, in summary, substances can indeed be made up of only one type of atom or particle, and such substances are referred to as pure elements or elemental substances.