Форми атомних орбіталей

There are four known shapes of atomic orbitals. First, what are the orbitals? They are s, p, d, and f - in that order You can remember them with the word "speedIfy", which may or may not be an actual word.

What are Atomic Orbitals?

Atomic orbitals describe the most likely location that electrons will be found around the nucleus of an atom. Every unique orbital can only contain up to two electrons. They are typically drawn as 3D space around the nucleus and there are different atomic orbital shapes. Orbitals also have phases or signs which represent different parts of the orbitals. The phases are mathematical functions, but often distinguished in orbital drawings with different shaded or colored lobes. Phases are separated by nodes. Nodes are places in an atom where the electrons will not be found.

Types of Atomic Orbitals

There are three common orbital types:

• s-orbital: spherical shaped orbital with no nodes.

• p-orbital: figure eight shaped orbital with two lobes and one node.

• d-orbital: shaped like a four-leaf clover in all, but one type. Always has two nodes

(Video) Orbitals, the Basics: Atomic Orbital Tutorial

by Crash Chemistry Academy

This video is a bit long, but it does a fantastic job of describing why orbitals have the shapes they do. You will see step-by-step how to build up these layers, starting with $s$ and going up to $f$. Finally, you will learn why all of this is even important in the first place.

From Plum Pudding to Orbits

In the 1890s, physical chemist J.J. Thompson's cathode ray experiment uncovered the electron. It was the first subatomic particle we discovered. So, it was the first time someone had contradicted Dalton's atomic theory. The atom was divisible into smaller components! It jumpstarted the quantum era.

We know that Thompson proposed the plum pudding model. He knew that electrons had a negative charge. But, atoms were neutral. So, he imagined the electrons embedded in a positively charged sphere. For many English chemists, it reminded them of the plum pudding dessert. So, that's how it got its moniker. But, difficulties with Thompson's model quickly arose. Soon after, nuclear chemists documented the first cases of radioactivity. It was unclear how the plum pudding model could explain such experiments.

In 1911, Ernest Rutherford performed his famous gold foil experiment. Rutherford's graduate student shot alpha particles (helium nuclei) at thin gold metal sheets. They expected the alpha particles to pass straight through. Why? Based on the plum pudding model, the atom is perfectly neutral. There were no distinct parts. Many of the alpha particles did traverse the foil. But a few got deflected back at steep angles. They had discovered the nucleus! Most of the atom's mass rests in a positively charged center. Rutherford published his nuclear model.

The discovery of the atomic nucleus raised several questions. For example, how do the electrons stay around the nucleus? Rutherford's model predicted that the electrons would spiral toward the nucleus. The protons and electrons would annihilate each other. The atomic nucleus should be inherently unstable. Max Planck helped to solve the problem during his work on blackbody radiation. He realized that the atomic spectra were quantized. Neils Bohr applied quantization to the electrons in the atom. Quantization produced the Bohr atomic model. The electrons circle the nucleus in fixed orbits. Each orbit had a specific energy. It was a massive step forward!

From Orbits to Orbitals

Bohr's atomic model still had problems. It accurately explained the atomic spectra for the hydrogen atom. No one else had done that. So, it was a significant improvement. But, for heavier elements, it didn't seem to work. The theoretical results approximated the experimental values for tiny elements. So the results for elements like helium and lithium were very similar. But, it became more and more inaccurate as they got larger.

Soon after, Erwin Schrodinger developed his quantum mechanical model. He created his famous equation. When you solve the equation, you get a wavefunction. The wavefunction is a mathematical function that contains all the properties of an electron. But, he didn't understand the physical meaning of the wavefunction. Why? The wavefunction has an imaginary component. So, it's unclear. To get rid of the imaginary number, we square the wavefunction. We interpret the squared wavefunction as a probability function. For example, the position probability results in the electron cloud. So, we can define a region where we are 95% likely to find our electron.

Why do Orbitals have Different Shapes

So, we understand that wavefunctions are mathematical functions that describe atomic orbitals. But remember, atoms are three-dimensional. When we solve the Schrodinger equation, we do so in three dimensions. It turns out that we can separate the components of each dimension. That's the quantum numbers. What happens when we isolate them? Each quantum number is a quantized component. This lets us solve the Schrodinger equation in spherical coordinates. The dimensions of spherical coordinates are the radius and two angles.

An orbital's shape gets governed by three quantum numbers. The first quantum number is the principal quantum number. It determines the orbital's size. For the valence electrons, it establishes the atomic radius. It also tells us about the electron's energy. The electrons closest to the nucleus have the lowest energy. When they are further from the nucleus, they have higher energy. The second quantum number is the azimuthal or the angular momentum quantum number. It defines the orbital's shape. It may seem strange that angular momentum describes shape. But angular momentum has a direction. So, it tells us about the electron's movement. The third quantum number is the magnetic number. It governs the orbital's orientation. It's a component within the angular momentum that limits its possible orientations.