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Atomic Structure

Electronic configuration and the building up principle

  • 3 things to know
  • Unit AS 1

Overview

Building up principle and hund's rule for filling a subshell.

What you need to know

Answer each one before you reveal it.

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Key term

State the building up principle.

Key term

Give the order in which the subshells are filled up to krypton.

Numbers

How many electrons can be held in the s, p and d subshells?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the building up principle.

    Model answer

    The building up principle states that electrons occupy the lowest energy orbital available before any higher energy orbital is filled.

  2. 2

    Give the order in which the subshells are filled up to krypton.

    Model answer

    The order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p.

  3. 3

    How many electrons can be held in the s, p and d subshells?

    Model answer

    An s subshell holds 2 electrons, a p subshell holds 6 and a d subshell holds 10.

  4. 4

    Why is the 4s subshell filled before the 3d subshell?

    Model answer

    The 4s subshell lies at a slightly lower energy than the 3d subshell when both are empty, so electrons enter 4s first.

  5. 5

    Write the full electronic configuration of a calcium atom.

    Model answer

    The configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

  6. 6

    Write the full electronic configuration of a bromine atom.

    Model answer

    The configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵.

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