Composition of Atoms: Electrons, Protons, Neutrons, Isotopes

 General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will give the ability to explain how and why models of atomic structure have changed over time. 

Composition of Atoms: Electrons, Protons, Neutrons, Isotopes
This will NOT surprise many people! 

If all matter is made of compounds and elements (and mixtures of them), and compounds are made of elements combined in specific, fixed ratios, and if elements are made of atoms… then…

What are atoms made of?

Let's just get right to it, eh?

Atoms are the smallest particle of any type of element that retains the chemical properties of that element.

Atoms are composed of protons, neutrons, and electrons. In a "stable" atom, the number of protons and electrons will always be the same.

Source: Google Search

The protons and neutrons are located in the center of the atom, a location called the nucleus. This seems like a definition.

The nucleus of an atom is the dense, central area of an atom wherein are located the protons and neutrons and which comprises the majority of an atom's mass.

The electrons are located outside the nucleus in orbitals, each having a unique energy level. The location of the orbitals can be thought of as clouds around the nucleus (that is to say, electron clouds).

More on those orbitals here.

https://www.google.com/search?q=electron+cloud+model

The number of protons in the nucleus determines the type of element. Saying it other ways:

• The number of protons found in the nucleus of any element is the atomic number for that element.
• The atomic number of any element is the number of protons found in the nucleus.

So… there we go… electron, protons, and neutrons. Let's look closer…

Three Types of Subatomic Particles

Proton — a positively charged subatomic particle that is found in the nucleus of an atom.

Symbol: p+

Relative charge: +1

Relative mass: 1

Actual mass: 1.674 X 10^-24

Location: In the nucleus

Electron — a negatively charged subatomic particle is found in the space outside the nucleus.

Symbol: e-

Relative charge: -1 

Relative mass: 1/1836

Actual mass: 9.11 X 10^-28

Location: In distinct orbitals surrounding the nucleus

Neutron — a neutral subatomic particle that is found in the nucleus of an atom.

Symbol: n

Relative charge: 0

Relative mass: 1

Actual mass: 1.675 X 10^-24

Location: In the nucleus

From the information above, a few conclusions:

Protons and neutrons are almost identical in mass.

Electrons are about "1/2000" the mass of a proton. (closer to 1/1836)

The neutron does not affect the charge of an atom. They just add mass.

If you add up the masses of  all of the parts of an atom you get something called by two names: atomic mass and atomic weight. They mean the same thing in most cases.

The atomic mass of an atom is the sum of the masses of all the parts of the atom. Since the electron is so much smaller, it is essentially the sum of the masses of the protons and neutrons.

Source: Google Search

However, some elements occur with different numbers of neutrons. There is, of course a name for this:

Any atom of an element (having the exact same number of protons) having different numbers of neutrons is called an isotope of that element.

For instance, hydrogen usually has 1 proton and 1 electron. However, an atom having 1 proton, 1 electron, PLUS 1 neutron is an isotope of hydrogen (because it has only 1 proton). Also, in the case of hydrogen, it gets a fancy name: deuterium.

When this is the case, the atomic mass of the element is the average atomic mass based on the relative composition of the various isotopes.