Mendeleev · Chemistry pathway · level 2

The mole: counting the invisible

The mole links microscopic entities to measurable quantities. One mole contains exactly 6.02214076 × 10²³ elementary entities.

The essential idea

The mole links microscopic entities to measurable quantities. One mole contains exactly 6.02214076 × 10²³ elementary entities.

Example

A mole of water and a mole of iron contain the same number of entities, but not the same mass.

Mini problem

How many entities are in 0.5 mol?

Show the solution

0.5 × 6.02214076 × 10²³ ≈ 3.011 × 10²³ entities.

Common mistake

Do not replace reasoning with a memorized rule. Always check geometry, units, coefficients or model assumptions.

Guided exercise

How many molecules are in 2.00 mol of water?

Show the detailed solution

N = n × Nₐ = 2.00 × 6.02214076 × 10²³ ≈ 1.204 × 10²⁴ molecules.

Avoid this

Always state what is being counted: molecules, atoms, ions or another entity.

Go further

The mole Explore tools

Mini calculator

From moles to particle count

N = n × Nₐ, with Nₐ = 6.02214076 × 10²³ mol⁻¹.

Amount n (mol)

Number of entities6.022 × 10²³

Key idea

The mole: counting the invisible

Key idea

The mole: counting the invisible

n = N/N_A · N_A = 6,02214076×10²³ mol⁻¹ (exact)

Before moving on, explain “The mole: counting the invisible” in two sentences without rereading the page. Then give one concrete example.

Guided example

The mole: counting the invisible

Before moving on, explain “The mole: counting the invisible” in two sentences without rereading the page. Then give one concrete example.

Put it into practice

The mole: counting the invisible

Choose a concrete case linked to The mole: counting the invisible. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.

Check your answer

A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.

Periodic table