Chemistry
Ions & ionic bonds
Why table salt is made of charged particles and salt water conducts electricity.
What you need first
You sprinkle salt into your pasta water without thinking much about it. Yet something amazing happens in the water: the salt breaks apart into tiny charged particles called ions. These very particles are the reason salt water conducts electricity and the reason salt holds together at all.
How atoms become ions
An atom is normally neutral: it has exactly as many (positive) as electrons (negative). But some atoms like to give electrons away, while others like to take them in. Sodium gives away one electron and then has one more positive charge than negative: it becomes the sodium ion Na⁺. Chlorine takes in one electron and becomes the chloride ion Cl⁻. Charged atoms like these are called ions. Some atoms even give away or take in two electrons at once: magnesium gives two away and becomes Mg²⁺, oxygen takes two in and becomes O²⁻. So the small superscript tells you by how many charges the ion is out of balance. Where there is no number, as with Na⁺ and Cl⁻, it is exactly one charge.
The proton count determines the element, the electrons determine the charge.
Opposites attract
Positive and negative charges attract each other. So Na⁺ and Cl⁻ pull in close together, and not just two of them but billions. They arrange themselves in a regular pattern called an ionic lattice. This firm hold is called an ionic bond, and you know the result well: table salt, chemically sodium chloride (NaCl). There is exactly one Cl⁻ for every Na⁺, which is why the crystal is neutral on the outside. That 1 to 1 ratio is what the formula NaCl states. Every grain of salt you hold in your hand is one of these lattices.
Why salt water conducts electricity
Current only flows when charged particles can move. In solid salt the ions are locked into the lattice, which is why a dry grain of salt does not conduct electricity. But if you dissolve salt in water, the water pulls the ions apart: Na⁺ and Cl⁻ float around freely. Now they can carry charge, and the salt water conducts electricity. Pure water, on the other hand, hardly conducts at all, because it lacks free ions. The ions also become mobile when the lattice melts, but table salt needs more than 800 °C for that.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
Sodium gives away one electron. What is formed?
Why do Na⁺ and Cl⁻ hold together in a salt crystal?
A sodium atom has 11 protons and 11 electrons. How many electrons does the ion Na⁺ have?
Match each term from the ions topic to the right explanation.
A chlorine atom has 17 protons and 17 electrons. How many electrons does the ion Cl⁻ have?
An atom that takes in an electron becomes … charged.
Where this leads