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Lesson · Grade 11 · Chemistry

Electrons in Orbitals: The Quantum Mechanical Model

  • Grade 11
  • Chemistry
  • 2 min 3 s
  • British Columbia
  • BC11-SC-01

A Bohr atom with neat circular orbits gives way to a probability cloud of dots, whose 90% edge is an orbital, which then becomes the spherical s orbital beside the three p dumbbells on the x, y and z axes. Alongside, a chart splits energy levels n = 1 to 4 into s, p, d and f sublevels with 1, 3, 5 and 7 orbitals, and shows that each orbital holds at most two electrons of opposite spin, so the sublevels hold 2, 6, 10 and 14.

Concept: The quantum mechanical model: electrons in orbitals

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In one sentence

The question this lesson answers

Where exactly is an electron inside an atom?

In the Bohr model, electrons circle the nucleus in fixed orbits, like planets around the Sun.

Transcript

What the lesson says

Where exactly is an electron inside an atom?

In the Bohr model, electrons circle the nucleus in fixed orbits, like planets around the Sun.

But electrons do not really move along neat, planet-like paths like these.

The quantum mechanical model gives no exact path, only the chance of finding the electron at each place.

Denser dots show where the electron is more likely to be, sparser dots where it is less likely.

A region where an electron is likely to be found is called an orbital.

Its edge is usually drawn where there is a 90 percent chance that the electron is inside.

Orbitals are grouped into main energy levels, numbered n equals 1, 2, 3, 4 and so on.

Each level splits into sublevels, named s, p, d and f.

Level n has n sublevels: level 1 has only s, level 2 adds p, level 3 adds d, and level 4 adds f.

Each type of sublevel has a set number of orbitals: s has 1, p has 3, d has 5 and f has 7.

The orbital we drew is an s orbital, a sphere centred on the nucleus.

The three p orbitals are dumbbells: one along the x axis, one along y, and one along z.

Each orbital holds at most two electrons, with opposite spins: one arrow up and one arrow down.

So an s sublevel holds up to 2 electrons, p holds 6, d holds 10 and f holds 14.

Electrons are found in orbitals, not fixed orbits, and each orbital holds at most two electrons.

Curriculum

Where this fits

British Columbia, Grade 11

Chemistry 11, Atoms and electrons: quantum mechanical model and electron configurationBC11-SC-01

Next: Writing Electron Configurations

The outcomes and strands follow the British Columbia curriculum.

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