Illustrated · 1 min
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If protons can't be added or removed to turn an element into other elements, how do chemical reactions manage to change substances into completely new things with different properties? The answer is electrons. Due to their movement and location, they are able to interact with other atoms and form bonds, creating new substances.
Image source: By Phrood CC BY 2.0, via Wikimedia Commons
The helium atom shown above is a Bohr model diagram, which means that the electrons are drawn located in a circular orbit around the nucleus. The actual locations of electrons are more complicated- there are different spaces that electrons move through called orbitals, which we'll learn about in later lessons. Each orbital can hold two electrons.
These orbitals are located at specific energy levels, which we'll refer to as electron shells. In Bohr model drawings, each electron shell will be shown as a larger circle around the nucleus and previous shells. After the first shell, which requires two electrons to be full, each shell requires 8 electrons. The reason for this has to do with the actual orbitals electrons are located in, and will be covered more soon.
Atoms with full shells are more stable, so bonds tend to form to create outer shells containing 8 electrons. This is called the octet rule.
Image source: By Ahazard.sciencewriter CC BY 2.0, via Wikimedia Commons
The noble gas neon, depicted above, has two full electron shells. The first shell can only hold two electrons, and the second holds eight. The s and p labels on this diagram demonstrate the kind of orbitals exist at each level.
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