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In 1913, Niels Bohr attempted to resolve the atomic paradox by ignoring classical electromagnetism’s prediction that the orbiting electron in hydrogen would continuously emit light. Instead, he incorporated into the classical mechanics description of the atom Planck’s ideas of quantization and Einstein’s finding that light consists of photons whose energy is proportional to their frequency. Bohr assumed that the electron orbiting the nucleus would not normally emit any radiation (the stationary state hypothesis), but it would emit or absorb a photon if it moved to a different orbit. The energy absorbed or emitted would reflect differences in the orbital energies according to this equation:

Δ E = E f E i = h ν = h c λ

In this equation, h is Planck’s constant and E i and E f are the initial and final orbital energies, respectively. The absolute value of the energy difference is used, since frequencies and wavelengths are always positive. Instead of allowing for continuous values for the angular momentum, energy, and orbit radius, Bohr assumed that only discrete values for these could occur (actually, quantizing any one of these would imply that the other two are also quantized). Bohr’s expression for the quantized energies is:

E n = k n 2 , n = 1 , 2 , 3 ,

In this expression, k is a constant comprising fundamental constants such as the electron mass and charge and Planck’s constant. Inserting the expression for the orbit energies into the equation for Δ E gives

Δ E = k ( 1 n 1 2 1 n 2 2 ) = h c λ

or

1 λ = k h c ( 1 n 1 2 1 n 2 2 )

which is identical to the Rydberg equation for R = k h c . When Bohr calculated his theoretical value for the Rydberg constant, R , and compared it with the experimentally accepted value, he got excellent agreement. Since the Rydberg constant was one of the most precisely measured constants at that time, this level of agreement was astonishing and meant that Bohr’s model was taken seriously, despite the many assumptions that Bohr needed to derive it.

The lowest few energy levels are shown in [link] . One of the fundamental laws of physics is that matter is most stable with the lowest possible energy. Thus, the electron in a hydrogen atom usually moves in the n = 1 orbit, the orbit in which it has the lowest energy. When the electron is in this lowest energy orbit, the atom is said to be in its ground electronic state (or simply ground state). If the atom receives energy from an outside source, it is possible for the electron to move to an orbit with a higher n value and the atom is now in an excited electronic state (or simply an excited state) with a higher energy. When an electron transitions from an excited state (higher energy orbit) to a less excited state, or ground state, the difference in energy is emitted as a photon. Similarly, if a photon is absorbed by an atom, the energy of the photon moves an electron from a lower energy orbit up to a more excited one. We can relate the energy of electrons in atoms to what we learned previously about energy. The law of conservation of energy says that we can neither create nor destroy energy. Thus, if a certain amount of external energy is required to excite an electron from one energy level to another, that same amount of energy will be liberated when the electron returns to its initial state ( [link] ). In effect, an atom can “store” energy by using it to promote an electron to a state with a higher energy and release it when the electron returns to a lower state. The energy can be released as one quantum of energy, as the electron returns to its ground state (say, from n = 5 to n = 1), or it can be released as two or more smaller quanta as the electron falls to an intermediate state, then to the ground state (say, from n = 5 to n = 4, emitting one quantum, then to n = 1, emitting a second quantum).

Questions & Answers

which one of the Lewis structure
muktar Reply
Lewis structure just shows Valence electrons
Cassie
what is a solution
Joy Reply
A liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent).
Gabby
what is an acid and base
Joy
acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (H+) ions. pH level less than 7  bases produce hydroxide (OH-) ions in solution. pH level greater than 7
Gabby
An acid is a substances when dissolve in water to produce hydrogen ion as the only positive ion or proton. while base is a substances when dissolve in water to produce hydroxide ion .
Lawal
acid is a substance that produce hydrogen ion as only positive ion when dissolve in water
Ayomide
what is flame
Daniel Reply
my new mix tape
Jake
What is Stoichiometry?
sayyam Reply
sir I don't know
favour
the relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers.
Gabby
A radioactive subtance has a half life of 20hrs what fraction of the original radioactive nuclear will remain in 80hrs
Onyewuchi Reply
1/16th
Ian
general properties of transition metal
Abdullahi Reply
form stable complexes Have high melting and boiling points Contain large charge/radius ratio Form compounds which are often paramagnetic Are hard and possess high densities Form compounds with profound catalytic activity Show variable oxidation states form coloured ions and compounds.
Gabby
pls how do i learn chemistry
am just tried of it😭🙏
Same here
Brianna
organic chem tutor, hell teach you everything.. take notes clearly in a notebook and read it before you go to sleep until you know every topic like the back of your hand
Professor
I find it very hard to understand and remember things I read please I need help. Is just as if chemistry is difficult to me
Precious
may God help us. .me writing jamb this year
pray it will favour me
get good or find something else. don't do it if you don't love it
Professor
what is dative bond?
Aleesa Reply
A coordinate covalent bond, also known as a dative bond or coordinate bond is a kind of 2-center, 2-electron covalent bond in which the two electrons derive from the same atom.
dharshika
how can i write iupac nunber
Emmanuel
In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry. It is published in the Nomenclature of Organic Chemistry
Nike
How can I know the logic for writing the configuration of an element?
Brianna
s and p diagram
Papa
I dont understand that
Brianna
what is elemental composition of earth
grace Reply
what if we try copper and the hydrogen what happened
Elizabeth Reply
law of definite proportion
Victor Reply
Law of Definite Proportion states that all pure samples of the same chemical compound contains the same elements in proportion by mass
Eunice
what is chemistry
Amos Reply
It is that branch of Science which deals with the study of composition, structure and properties of matter .... Ok
ShAmy
The branch of natural science that deals with the constitution of substances and the changes that they undergo as a consequence of alterations in the constitution of their molecules
Young
what is the constitution of substance
ShAmy
chemistry is the study of matter and the changes it undergoes.
Bernard
picture of periodic table
Tessy Reply
what is matter
Emmaworldwide Reply
matter is any thing that has weight or mass and can occupy spaces
Bernard
What are the classes of colloid
Ilo Reply
Practice Key Terms 4

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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