Argon (Ar): Bohr Model, Protons, Neutrons & Electrons
Argon is element number 18, a noble gas in group 18, period 3. Its atom has 18 protons, 22 neutrons and 18 electrons arranged in 3 shells: 2, 8, 8.
- 18 protons
- 22 neutrons
- 18 electrons
Protons, neutrons and electrons in argon
Le atomic number of argon is 18, so every argon atom has 18 protons. A neutral atom has the same number of electrons, 18. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For argon-40, that is 40 − 18 = 22 neutrons. Argon has 3 stable isotopes, with 18, 20, 22 neutrons.
How to draw the Bohr model of argon
- Draw the nucleus and write 18 p⁺ et 22 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 8 electrons on it.
- Check: 2 + 8 + 8 = 18 electrons, the same as the number of protons.
Electron configuration
The electron configuration of argon is [Ne] 3s² 3p⁶. Its 8 outer electrons decide how it reacts: its outer shell is full, so it hardly reacts at all.
Key facts about argon
| Symbol | Ar |
|---|---|
| Atomic number | 18 |
| Relative atomic mass | 39.948 |
| Group · period · block | group 18 · period 3 · p-block |
| Type | Gaz noble |
| State at 25 °C | gas |
| Couches électroniques | 2, 8, 8 |
| Electron configuration | [Ne] 3s² 3p⁶ |
| Électrons de valence | 8 |
| Common ion | none: its outer shell is already full |
| Electronegativity (Pauling) | — |
| First ionisation energy | 15.76 eV (1521 kJ/mol) |
| Atomic radius (empirical) | — |
Où argon sits on the periodic table
Foire aux questions
How many protons, neutrons and electrons does argon have?
Argon has 18 protons and 18 electrons (atomic number 18). Its most common isotope, argon-40, has 40 − 18 = 22 neutrons.
What is the electron configuration of argon?
[Ne] 3s² 3p⁶. In shells that is 2, 8, 8.
How many valence electrons does argon have?
8. Argon is in group 18, and its outer shell holds 8 electrons.
Where is argon on the periodic table?
In group 18, period 3, in the p-block. It is a noble gas.
