Classical vs Quantum Mechanics
You are used to the way everyday objects behave, and you will have developed an ability to unconsciously understand and predict the movement of objects.
You judge traffic when you want to cross a road because you have an understanding of their motion.
You instantly visualise how and when your phone will hit the floor the moment it slips from your hand because you have a comprehension of gravity.
You automatically know where to run or throw or jump or swing a racquet if you’re playing a sport because you know how the ball moves.
And you know that someone has taken your chocolate from the fridge because objects can’t move from a location without someone or something making that happen.
You know all these things because stuff always behaves in a predictable manner. All stuff. Even things that are so small you can only see them through the lab microscope.
All these objects are obeying classical mechanics (also known as Newtonian mechanics) There are equations that describe the motion and the effects of force on objects (or “bodies”, as physics describes them).
What can you learn about quantum mechanics from coffee? Or from a flight of stairs? You can listen to me simplify the concept of quantum mechanics using these as analogies.
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Where Does Quantum Theory Come Into It?
But not everything behaves like that. The tiniest particles behave in a way that we wouldn’t recognise and couldn’t predict. You might describe their behaviour as mysterious, bizarre, or plain weird. They behave according to quantum mechanics rather than classical mechanics.
We’re going to look at quantum mechanics in the simplest terms. There’s no need for us to go into great depth at this level. Before we go on let’s be more specific about which particles we are talking about.
Quantum theory describes the behaviour and characteristics of individual molecules, atoms, and even smaller particles such as electrons and photons. At this level, we will focus on how quantum mechanics describes the characteristics of electrons, and the implications on atomic structure and hence the changes to the atomic model you now encounter.
How the Electron’s Nature Shapes the Atom
Quantum theory tells us that electrons have certain characteristics that describe their position in an atom. A quantum number is used to describe each of these four characteristics, four quantum numbers in all.
The value of one quantum number, the principal quantum number, defines which shell the electron is located in.
Two more quantum numbers define which orbital type the electron is located in, and specifically which orbital within that orbital type.
A fourth quantum number defines which spin condition an electron has. Electrons have two possible spin conditions, usually referred to as spin up and spin down. This is important because each orbital may accommodate up to two electrons, but these must have opposite spin to each other.
We’ll go into the topic of atomic orbitals, and their associated “rules” in our next episode.
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