Learning Objectives

describe what spectra are. Discover the quantum numbers that room assigned come electrons.

There space two basic ways that generating light: either heat things up so warm it glows or pass an electrical existing through a sample of issue (usually a gas). Incandescence lights and fluorescent lights generate light via these 2 methods, respectively.

You are watching: Which quantum number determines the energy of an electron in a hydrogen atom

A hot object provides off a continuous of light. We notification this when the visible section of the electromagnetic spectrum is passed v a prism: the prism the end light right into its constituent colors, and also all color are current in a consistent rainbow (part (a) in number 8.3 \"Prisms and also Light\"). This picture is known as a constant spectrumAn picture that consists of all color of light.. However, when electrical power is passed v a gas and also light is emitted and this irradiate is passed despite a prism, we view only specific lines of light in the picture (part (b) in number 8.3 \"Prisms and Light\"). This picture is called a heat spectrumAn photo that contains only specific colors of light.. It turns out that every element has its very own unique, characteristic line spectrum.

Figure 8.3 Prisms and Light


(a) A glowing object gives off a complete rainbow that colors, which room noticed only when light is passed with a prism to do a constant spectrum. (b) However, when electrical power is passed through a gas, only details colors that light room emitted. Below are the color of light in the heat spectrum the Hg.

Why walk the light emitted indigenous an electrically excited gas have only certain colors, while light given off by hot objects has actually a consistent spectrum? because that a long time, the was not well explained. Particularly simple to be the spectrum of hydrogen gas, which can be described easily by an equation; no other aspect has a spectrum the is therefore predictable (Figure 8.4 \"Hydrogen Spectrum\"). Late-nineteenth-century scientists found that the location of the lines obeyed a pattern given by the equation

1λ=(109,700 cm−1)(14−1n2)

where n = 3, 4, 5, 6,…, but they could not describe why this to be so.

Figure 8.4 Hydrogen Spectrum


The spectrum that hydrogen was particularly simple and could it is in predicted through a straightforward mathematical expression.

In 1913, the Danish scientist Niels Bohr suggested a factor why the hydrogen atom spectrum looked this way. He said that the electron in a hydrogen atom might not have any kind of random energy, having actually only certain fixed worths of energy that were indexed by the number n (the exact same n in the equation over and now called a quantum numberAn table of contents that coincides to a property of one electron, choose its energy.). Quantities that have actually certain certain values are dubbed quantizedWhen a amount is minimal to having actually only certain values. Values. Bohr argued that the power of the electron in hydrogen was quantized because it remained in a certain orbit. Since the energies of the electron deserve to have only particular values, the changes in energies can have only particular values (somewhat similar to a staircase: not only are the stairs steps collection at details heights however the height in between steps is fixed). Finally, Bohr said that the power of irradiate emitted native electrified hydrogen gas was equal to the energy difference of the electron’s power states:


This means that only specific frequencies (and thus, particular wavelengths) the light room emitted. Number 8.5 \"Bohr’s design of the Hydrogen Atom\" mirrors a design of the hydrogen atom based on Bohr’s ideas.

Figure 8.5 Bohr’s version of the Hydrogen Atom


Bohr’s description of the hydrogen atom had certain orbits because that the electron, which had actually quantized energies.

Bohr’s concepts were valuable but were applied only come the hydrogen atom. However, later researchers generalized Bohr’s ideas into a new theory dubbed quantum mechanicsThe theory of electrons the treats them together a wave., which defines the habits of electrons as if they were acting as a wave, not as particles. Quantum mechanics predicts two significant things: quantized energies because that electrons of all atoms (not just hydrogen) and also an company of electrons within atoms. Electrons are no much longer thought of together being randomly distributed about a nucleus or minimal to certain orbits (in the regard, Bohr to be wrong). Instead, electrons are built up into groups and also subgroups that define much about the chemical habits of the atom.

In the quantum-mechanical design of one atom, the state of an electron is described by four quantum numbers, not simply the one predicted by Bohr. The first quantum number is called the major quantum numberThe table of contents that greatly determines the power of an electron in one atom. Represented by n. (n). The major quantum number mainly determines the energy of one electron. Electrons in the same atom that have the same primary quantum number are said to accounting an electron shellA term supplied to describe electrons with the same major quantum number. That the atom. The major quantum number have the right to be any kind of nonzero positive integer: 1, 2, 3, 4,….

Within a shell, there might be multiple feasible values the the next quantum number, the angular momentum quantum numberAn index that affects the energy and also the spatial circulation of one electron in one atom. Stood for by ℓ. (ℓ). The ℓ quantum number has actually a minor impact on the energy of the electron but additionally affects the spatial distribution of the electron in three-dimensional space—that is, the form of one electron’s circulation in space. The value of the ℓ quantum number can be any type of integer in between 0 and n − 1:

ℓ = 0, 1, 2,…, n − 1

Thus, because that a provided value of n, there space different feasible values the ℓ:

and for this reason forth. Electrons within a shell that have actually the very same value that ℓ are stated to accounting a subshellA term offered to define electrons in a covering that have actually the very same angular inert quantum number. In the atom. Commonly, instead of referring to the numerical worth of ℓ, a letter represents the worth of ℓ (to aid distinguish the from the principal quantum number):

The next quantum number is dubbed the magnetic quantum numberthe index the determines the orientation of the electron’s spatial distribution. Stood for by mℓ. (mℓ). For any value the ℓ, there are 2ℓ + 1 possible values of mℓ, ranging from −ℓ come ℓ:

−ℓ ≤ mℓ ≤ ℓ


|mℓ|≤ ℓ

The following explicitly lists the possible values the mℓ for the feasible values the ℓ:

If ℓ amounts to The mℓ values can be
0 0
1 −1, 0, or 1
2 −2, −1, 0, 1, or 2
3 −3, −2, −1, 0, 1, 2, or 3

The details value that mℓ dictates the orientation of one electron’s circulation in space. When ℓ is zero, mℓ can be just zero, so over there is just one possible orientation. As soon as ℓ is 1, there room three possible orientations because that an electron’s distribution. As soon as ℓ is 2, there are five feasible orientations that electron distribution. This walk on and also on for various other values of ℓ, yet we need not think about any greater values of ℓ here. Each worth of mℓ designates a certain orbitalThe specific set of principal, angular momentum, and magnetic quantum numbers because that an electron.. Thus, over there is just one orbital when ℓ is zero, 3 orbitals when ℓ is 1, 5 orbitals as soon as ℓ is 2, and also so forth. The mℓ quantum number has no impact on the energy of an electron uneven the electrons room subjected come a magnetic field—hence that is name.

The ℓ quantum number dictates the basic shape of electron circulation in an are (Figure 8.6 \"Electron Orbitals\"). Any s orbit is spherically symmetric (part (a) in number 8.6 \"Electron Orbitals\"), and there is only one orbital in any type of s subshell. Any kind of p orbital has actually a two-lobed, dumbbell-like form (part (b) in figure 8.6 \"Electron Orbitals\"); because there room three of them, we typically represent them as pointing follow me the x-, y-, and z-axes the Cartesian space. The d orbitals are four-lobed rosettes (part (c) in figure 8.6 \"Electron Orbitals\"); they are oriented in different way in space (the one labeling dz2 has two lobes and also a torus instead of four lobes, however it is identical to the various other orbitals). As soon as there is more than one feasible value of mℓ, every orbital is labeled with one of the possible values. It must be provided that the diagrams in figure 8.6 \"Electron Orbitals\" are estimates of the electron circulation in space, not surfaces electron are solved on.

Figure 8.6 Electron Orbitals


(a) The lone s orbital is spherical in distribution. (b) The 3 p orbitals space shaped favor dumbbells, and each one points in a different direction. (c) The 5 d orbitals room rosette in shape, other than for the dz2 orbital, i m sorry is a “dumbbell + torus” combination. They room all oriented in various directions.

The last quantum number is the turn quantum numberThe index that indicates one of two spin claims for one electron. Represented by ms. (ms). Electrons and other subatomic particles behave as if they are spinning (we can not tell if they yes, really are, however they behave together if they are). Electrons themselves have actually two possible spin states, and also because of mathematics, they room assigned the quantum numbers +1/2 and −1/2. These are the just two feasible choices because that the turn quantum number of an electron.

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Example 3

Of the set of quantum numbers n, ℓ, mℓ, ms, i beg your pardon are possible and which space not allowed?

3, 2, 1, +1/2 2, 2, 0, −1/2 3, −1, 0, +1/2


The principal quantum number n must be an integer, which it is here. The quantum number ℓ have to be less than n, which that is. The mℓ quantum number have to be between −ℓ and ℓ, which the is. The turn quantum number is +1/2, which is allowed. Since this set of quantum numbers follows all restrictions, that is possible. The quantum number n is an integer, but the quantum number ℓ need to be much less than n, which that is not. Thus, this is not an allowed set of quantum numbers. The major quantum number n is one integer, however ℓ is not allowed to be negative. Therefore this is not an allowed collection of quantum numbers.

Test Yourself

Of the collection of quantum number n, ℓ, mℓ, ms, i m sorry are possible and which space not allowed?

4, 2, −2, 1 3, 1, 0, −1/2


Spin must be either +1/2 or −1/2, for this reason this set of quantum number is not allowed. Enabled

Chemistry Is Everywhere: Neon Lights

A neon light is usually an electrified tube through a tiny amount of gas in it. Electricity excites electron in the gas atoms, i beg your pardon then provide off light as the electrons go earlier into a lower energy state. However, numerous so-called “neon” lights don’t contain neon!

Although we know now the a gas discharge provides off only certain colors of light, without a prism or other component to separate the individual irradiate colors, we watch a composite of every the colour emitted. It is not unusual for a specific color come predominate. True neon lights, through neon gas in them, have a reddish-orange light because of the huge amount of red-, orange-, and yellow-colored light emitted. However, if you usage krypton instead of neon, you gain a whitish light, while using argon returns a blue-purple light. A light filled with nitrogen gas glows purple, together does a helium lamp. Other gases—and mixture of gases—emit various other colors the light. Ironically, in spite of its importance in the advancement of modern-day electronic theory, hydrogen lamps emit little visible light and are rarely supplied for illumination purposes.

Key Takeaways

electron in atoms have actually quantized energies. The state of electron in atom is defined by four quantum numbers.

Under what scenarios is a constant spectrum formed? Under what circumstances is a heat spectrum formed?