The p orbitals at the second energy level are called 2px, 2py and 2pz. This is simply for convenience, because what you might think of as the x, y or z direction changes constantly as the atom tumbles in space. These are arbitrarily given the symbols px, py and pz. The one shown below points up and down the page.Īt any one energy level, we have three absolutely equivalent p orbitals pointing mutually at right angles to each other. Unlike an s orbital, a p orbital points in a particular direction. However, at the second level, there are also orbitals called 2p orbitals in addition to the 2s orbital. At the first energy level, the only orbital available to electrons is the 1s orbital. We call this surface a node or a nodal surface.Ī 3s orbital is even larger, and it has three nodes. There is a surface between the two balls where there is zero probability of finding an electron. It is sort of like a hollow tennis ball.Ī 2s orbital is similar to a 1s orbital, but it has sphere of electron density inside the outer sphere, like one tennis ball inside another. If you look carefully, you will notice that a 1s orbital has very little electron density near the nucleus, but it builds up to a maximum as you get further from the nucleus and then decreases beyond the contour. Now, let’s look at a cross-section of these orbitals. The order of size is 1s < 2s < 3s < …, as shown below. As the energy levels increase, the electrons are located further from the nucleus, so the orbitals get bigger. We call this shape the 95% contour.Īn s orbital is spherically symmetric around the nucleus of the atom, like a hollow ball made of rather fluffy material with the nucleus at its centre. All we can do is draw a shape that will include the electron most of the time, say 95% of the time. Since an electron can theoretically occupy all space, it is impossible to draw an orbital. All we have to do is remember the shapes that correspond to each letter. The letters s, p, d, and f were assigned for historical reasons that need not concern us. The letters go in the order s, p, d, f, g, h, i, j, etc. The letter refers to the shape of the orbital. Thus 1 refers to the energy level closest to the nucleus 2 refers to the next energy level further out, and so on. The number denotes the energy level of the electron in the orbital. Each orbital is denoted by a number and a letter.
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