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Abbreviations:   p = protons, e = electronsm n = neutrons

The atomic number of an element is also called a proton number

This tells you the # of protons in an atom.

A normal atom has a neutral charge:

    Equal numbers of + and – particles.

    # e = # p

Ions are atoms with extra electrons, or missing electrons.

When atom is missing e, then it has a + charge

When atom has extra a, then it has a – charge

Ions have completely different behaviors than neutral atoms.

Consider Na (a neutral sodium atom) = highly explosive

But Na easily loses e.  So we formally find it as a + charged ion.

Na + = non-explosive, and in every cell in our bodies. Essential for cell activity. You’d die in an instant without this.

Sodium ion

Cl (neutral, atom) = always forms Cl2 molecules. Deadly poison gas.

Cl-  = non-poison, and in every cell in our body.

Essential for cell activity. You’d die in an instant without this.

Example: Calcium atoms usually lose 2 e, as shown here.

Calcium Atom and Ion

When 2 neutral atoms get close, one can pull off the other’s electron

Na and Cl atoms forming ions Sodium Chlorine

Chlorine: terminology

People sometimes use the same word to describe different things. For example, “chlorine” can refer to:

A. Chlorine atom – a single, neutral, chlorine atom. These are unstable. We normally never encounter one. They bind to each other to form chlorine molecules.

B. Chlorine molecule (Cl2) – deadly gas

C. Chlorine ion – A chlorine atom that picked up an electron. In small quantities these are essential for life.

D. Chlorine bleach aka sodium hypochlorite (NaOCl)
This is a disinfectant used to kill bacteria in swimming pools. What is the chemical structure of sodium hypochlorite ?

We can visualize the electron distribution in sodium hypochlorite a little more accurately


How to make sodium hypochlorite?

Add chlorine gas (Cl2) to caustic soda (NaOH).

Cl2 + 2NaOH + → NaOCl + NaCl + H2O

How does sodium hypochlorite disinfection work? By adding hypochlorite to water, hypochlorous acid (HOCl) is formed.

NaOCl + H2O → HOCl + NaOH

This hypochlorous acid is then broken down into hydrochloric acid (HCl) and oxygen (O). This acid will kill most bacteria, viruses and fungi.


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