Introduction

The atom is the fundamental building block that makes all the physical matter in the universe. Atoms make up practically everything in our daily lives from the air we breathe to the electronics we use. In order to understand chemistry, we have to develop an understanding of how an atom is structured. In future sections, we will use this understanding to see how atoms are joined together to form compounds.

<aside> 💡 Note: This section introduces scientific notation and dimensional analysis. This section has not been written yet so please brush up on it using other resources.

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Subatomic Particles

https://www.youtube.com/shorts/diD46jTGeoE

Atoms are known as the fundamental building blocks of matter, but they are actually made of subatomic particles. In fact, subatomic particles are made up of even smaller particles called quarks, but in this section, we’ll limit ourselves to protons, neutrons, and electrons.

Protons are positively charged particles (think ‘p’ for positive) that are located in the nucleus (center) **of an atom. The number of protons in the nucleus defines the **atomic number ****of an element. For instance, every atom with 1 proton is hydrogen, and every atom with 6 protons is carbon.

As of 2024, there are 118 elements on the periodic table. The mass of a proton, $m_p$, is extremely small:

$$ m_p=1.67262\times10^{-27} \,kg $$

Note how unfathomably small this mass is! $10^{-27}$ indicates the leading value is proceeded by 26 0s!

$$ m_p=0.00000000000000000000000000167262\,kg $$

Since this mass is incredibly small, we need a unit to standardize masses near this scale. The mass of the proton, $m_p$ is defined as follows:

$$ m_p=1.67262\times10^{-27} \,kg $$

Neutrons are neutral; they have no charge (think ‘n’ for ‘neutral’). They live in the nucleus next to the protons. They too have an small mass, $m_n$, approximately equal to that of a proton.

$$ m_n=1.67262\times10^{-27} \,kg $$

Electrons are negatively charged particles that orbit the nucleus in regions known as orbitals. They have a charge equal and opposite to that of a proton. The mass of an electron, $m_e$, is even smaller than that of the proton and neutron.

$$ m_e=9.10939\times10^{-31} \,kg $$

<aside> 💡 Table 1.2.1: The Mass and Charge of Subatomic Particles

The proton and electron carry a magnitude of charge equal to $1.6\times10^{-19} C$.

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Now that we know what atoms are made of, next we’ll draw some pictures of atoms.