Protons — Structure & Properties

Protons

• Protons are positively charged particles that help make up the atom

• Protons are located in the nucleus of the atom (along with neutrons)

What Is a Proton?

• Protons are subatomic particles that make up an atom, they contain a positive charge and help make up the mass of the atom

Protons are the positively charged sub-atomic particles. They have a mass of 1 AMU, or Atomic Mass Unit, which is the same as that of neutrons. These two types of particles are located together in the nucleus at the center of the atom.

The number of protons in an atom, called the atomic number, determines what element that atom is. Chemical interactions occur primarily between electrons, and they cannot change proton count. Therefore, no reaction can change one element into another.

Protons are a positively charged particle found in the nucleus of atoms. They have a mass of approximately 1 AMU. Protons carry an electric charge of +$1$ $e$ (elementary charge), or $1.60218\cdot 10^{-19}$ coulombs.

Protons are composed of quarks, elementary particles that cannot be broken into smaller components. Specifically, protons are composed of 2 up quarks, and 1 down quark. Up quarks carry a charge of +$\frac{2}{3}\text{ }e$ and down quarks carry a charge of -$\frac{1}{3}\text{ }e$, resulting in a total charge of +$1\text{ }e$ for the proton. The interaction of quarks plays a heavy role in beta radiation.

Protons are responsible for the identity of an atom. The number of protons that an atom contains is referred to as the atomic number. If an atom has 5 protons then its atomic number must be 5, and if its atomic number is 5, it must have 5 protons.

(Video) Protons, Neutrons, and Electrons (Intro to Subatomic Particles!)

by Robin Reaction

This video will give you an introduction to protons, neutrons, and electrons. You will learn how they are similar and different in terms of their charge, location, and mass.

Discovery of the Proton

Ernest Rutherford was an incredibly famous physical chemist. We've already looked at some of his work. In 1911, his gold foil experiment led to the discovery of the atomic nucleus. The data suggested a new atomic model. The plum pudding model was obsolete. Instead, he proposed the nuclear model. Today, we know Rutherford's model was also incomplete. We still needed the Bohr model and the quantum mechanical model. But it was still a massive step forward. So far, that's what we know about Rutherford. But he's famous for another reason. He discovered the proton!

In 1917, Rutherford made a crucial observation. He fired alpha particles (helium nuclei) into the air. What was the result? His detectors recorded hydrogen nuclei. What's happening? Our atmosphere is largely composed of nitrogen. When an alpha particle hits a nitrogen nucleus, it undergoes a nuclear reaction. The reaction's products are an oxygen-17 atom and a hydrogen ion. We can write the nuclear equation as $^{14}N+ \alpha \rightarrow ^{17}O + H^{+}$. As a side note, the equation uses isotope notation. Oxygen-17 is a rare isotope called heavy oxygen.

After observing the air-based reaction, Rutherford conducted the experiment in pure nitrogen gas. The results got amplified! Rutherford considered the experimental results. We knew that hydrogen was the smallest element. But, Rutherford also assumed hydrogen was a building block for larger atoms. His assumption was based on earlier work by William Prout. Prout thought that all chemical elements consisted of hydrogen atoms. He founded his conclusion on the atomic masses. Unfortunately, at the time, the atomic mass data wasn't accurate. He made the correct conclusion from inaccurate data. Even so, he deduced that hydrogen was the fundamental component of an atom's nucleus. Rutherford's experiment showed hydrogen could get ejected from another element's nucleus. So, it must be the fundamental particle. He named the particle the proton from the Greek word meaning first.

Facts about Protons

Here are a few facts about protons that you need to know for general chemistry.

• Protons, along with neutrons, are nucleons. They reside in the atomic nucleus and get held together by the strong nuclear force.

• The mass of a proton is one atomic mass unit (amu). In kilograms, that's $1.672\times 10^{-27}$.

• As a side note, the masses of protons and neutrons are slightly different. The neutron is barely larger ($0.14$ percent). But we generally say they are both one amu. The difference comes from the number of quarks that make up both particles. But that's really advanced physics.

• The most common isotope of hydrogen, protium, is a single proton. It has a natural abundance of $99.98$ percent.

• Protons have a charge of one positive elementary charge ($+1e$). The elementary charge equals $1.602\times10^{-19}$ Coulombs.

• Protons and electrons have equal but opposite charges. The electrostatic attraction between them holds the electrons in their orbitals.

Protons and Chemistry

Protons play a vital role in chemistry. The number of protons in the nucleus decides the atomic number. On the periodic table, the atomic number determines the element's identity. Let's say a nucleus has six protons. What's its identity? It's always an oxygen atom. In neutral atoms, the number of protons and electrons is equal. But, it's the valence electrons that determine the element's chemical properties.

Protons also play an important role in acid-base reactions. We'll study this in more detail in future lessons. But, an Arrhenius acid is any compound that increases the hydrogen ion concentration. But hydrogen ions are just protons! So, an entire set of chemical reactions depends on proton exchanges. You'll also see this in biology. For example, do you remember learning about the electron transport chain? In the mitochondria, it pumps protons across the mitochondrial membrane. The mitochondria use the energy created by the charge gradient for ATP synthesis.