Electron Shells & Atomic Structure

Electron Shells

• Describes how electrons are arranged into shells within an atom.
• Explanation of structure and rules of the electron shell in the atomic model.
• Structure and properties of atoms relate to the organization of elements in the periodic table.

Connecting the Dots - Prior Knowledge

• Year 7: Matter is made of particles, and the particle model explains the behavior and arrangement of particles.
• Year 8: Atoms from the same element are alike but different from atoms of other elements.
• Year 9: Atoms are made of a positive nucleus (protons and neutral neutrons) surrounded by negative electrons.
• Year 10: the atomic structure and properties of elements are used to organize them in the periodic table

Intro to Atoms

• The atomic model has evolved over time with shared experimental evidence.
• Atom: The smallest unit of matter.
• Orbits: Pathways around the nucleus.
• Dalton (1803): Atoms are indivisible and indestructible.
• Thomson (1904): The 'plum pudding' model, where electrons are dispersed within a positive sphere.
• Rutherford (1911): The atom is mostly empty space with a central positive nucleus, and electrons orbit in random positions.
• Bohr (1913): Electrons travel around the nucleus in orbits at specific energy levels.

The Bohr Model

• Niels Bohr (1885-1962) was a Danish physicist who created the model of the atom.
• Electrons orbit the nucleus at set distances in 'shells,' similar to layers of an onion or planets orbiting a sun.
• Bohr's model furthered the Rutherford model of electrons orbiting in random positions.
• Earlier models described electrons as randomly positioned or orbiting the nucleus.
• Bohr proposed electrons only exist in specific orbits named 'electron shells'.

Electron Shell Diagrams

• Electron shells, according to the Bohr model, can be represented by circles of increasing size surrounding the nucleus.
• Electrons in fixed orbits move around the nucleus at a set distance.
• A neon (Ne) atom has 10 electrons across two shells
• There are 2 electrons in the innermost shell
• The valence shell has 8 electrons
• Electron shells: Energy levels around the nucleus.
• Valence shell: The outermost electron shell.
• The Bohr model is called the "planetary model" since electrons orbit the nucleus like planets orbit a sun.

Rules for Electron Shells

• There is a limit to the total number of electrons in one shell, determined by rules.
• Shells closer to the nucleus have lower energy and are filled first before filling more distant shells.
• Electron shell rules state to occupy the shell closest to nucleus first
• The maximum number of electrons in increasing shells is 2, 8, 8, 2.

Electrons can gain or lose energy

• Chemical substances produce colored light when exposed to heat.
• Energy causes electrons in their 'ground' state to absorb energy and "jump" to a higher energy shell (excited).
• Excited electrons fall back to their ground state almost immediately.

Spectroscopy

• Colored light from electron jumping can be seen using a spectroscope.
• A spectroscope is a specialized instrument that breaks light into colors.
• Each element produces a different emission spectrum when conducting a flame test.
• Emission Spectrum: The unique pattern of that appears on a spectroscope.
• Every element emits a different light composition due to different electron shell configurations.
• Bohr used hydrogen's line emission spectra to explain energy levels.
• Emission spectra can identify elements, and serves as 'fingerprints' for recognition.
• The sun is partly made of Oxygen and Helium as determined with spectroscopy.

Electrons in action: fireworks

• Fireworks illustrate excited electrons reverting to their original shells.
• Specific metal elements absorb heat from chemical reactions thus exciting them.
• Electrons emit a range of colors, determined by the metal, as they return to their shells:
• Sodium (Na): Yellow
• Copper (Cu): Blue
• Strontium (Sr): Deep red