L9. Subatomic Particles

Atoms and the Periodic Table

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L9. Subatomic Particles

How do the tiny parts inside an atom — protons, neutrons, and electrons — explain why atoms behave the way they do?

Why this lesson matters (a quick connection)

You already learned what an atom is and that each element has its own identity. This lesson looks inside that atom to the particles that make the identity and behavior possible. We will use a simple particle-level model to explain two everyday observations: why atoms are usually neutral, and how an atom can become charged. A short phenomenon to keep in mind: a balloon rubbed on a sweater can stick to a wall. That sticking happens because electrons move between materials — a process explained by subatomic particles.

Meet the three subatomic particles

An atom is built from three kinds of particles. Each kind has a typical charge, a relative mass, and a usual place in the atom. Learn these so you can read particle-level diagrams and reason about charge and mass.

• Protons (p+): positive charge +1 elementary charge (+1 e). Found in the nucleus. Relative mass ≈ 1.67 × 10^-27 kg (about 1 atomic mass unit). Neutrons (n0): neutral, charge 0. Found in the nucleus. Relative mass ≈ 1.67 × 10^-27 kg (about 1 atomic mass unit). Electrons (e-): negative charge −1 elementary charge (−1 e). Move in the space around the nucleus. Relative mass ≈ 9.11 × 10^-31 kg (about 1/1836 of a proton).

How particle counts set identity and charge

Count the protons to identify an element: the proton count is the atomic number. For a neutral atom, the number of electrons equals the number of protons so total charge is zero. If electrons are added or removed, the particle counts change and the atom becomes an ion (charged particle). Think of electrons as the more mobile pieces that are lost or gained in everyday charging or in chemistry.

• Neutral atom example: If a carbon atom has 6 protons, it has 6 electrons (6 p+ and 6 e-) → net charge 0. Ion example (loss of an electron): Na → Na+ + e- . Atoms conserved: 1 Na on both sides. Charge conserved: 0 = (+1) + (−1). Ion example (gain of an electron): Cl + e- → Cl− . Atoms conserved and charge conserved: (+0) + (−1) = (−1).

Everyday application: balloon, wool, and particle exchange

When you rub a balloon on wool, tiny transfers of electrons happen at the surfaces. Wool tends to lose electrons and the balloon tends to gain them. The balloon becomes negatively charged (extra electrons) while the wool becomes positively charged (missing electrons). The charged balloon can attract neutral objects by polarizing their charges or attract opposite charges directly. At the particle level, nothing mysterious is created or destroyed: electrons move from one object to another, conserving atoms and total electric charge. This simple transfer explains static cling and sets the stage for later chemical ideas about ions and bonding.

Big idea

Protons, neutrons, and electrons are the building blocks inside atoms. Protons set the element identity, neutrons add mass without changing charge, and electrons control electrical charge and movement between atoms or materials.

By tracking counts of protons and electrons you can predict whether an atom is neutral or an ion, and by following simple particle-level diagrams you can explain everyday effects (like a rubbed balloon sticking to a wall) while conserving atoms and electric charge.