When the electron jumps from an excited state to lower state in hydrogen atom an atom Cannot emit?

The Hydrogen emission series

The electron in the ground state energy level of the hydrogen atom receives energy in the form of heat or electricity and is promoted to a higher energy level.

It cannot remain at a higher level (excited state) for very long, and falls back to a lower level.

When the electron falls back down (relax) it must lose the energy difference between the two energy levels. This loss of energy is performed by releasing electromagnetic energy in the form of infrared, visible light or ultraviolet radiation.

Movement of electrons between the shells is called electron transitions.

When electron transitions take place the energy emitted can be detected and its wavelength measured. This provides information about the relative energies of the shells.

In the hydrogen atom (the simplest case with only one electron to 'jump' between shells) the energy emitted appears in several series of lines, each series corresponding to electrons falling back to different levels. This is shown in the diagram below.

The Lyman series corresponds to transitions between the higher shells and the lowest shell (ground state). The energy of these transitions produces radiation in the ultra-violet region of the spectrum

The energy shells are usually given a letter 'n' to describe the specific energy level. The lowest level is n=1, the second level is n=2 etc.

Transitions from higher shells (n>2) to n=2 produce radiation in the visible region of the spectrum. It can be seen by splitting the light using a prism or diffraction grating and projecting it onto a screen.

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Convergence

As the energy levels increase in energy they get closer together. In other words level 2 and level 3 are further apart than level 3 and level 4. The levels converge towards a limit.

Transitions that occur in any series must also converge towards a high energy limit, as the largest transition is between the highest energy level and the level that is characteristic of the specific series.

The highest level is sometimes refered to as the 'infinite' level, as the levels get so close together where they converge that they are impossible to count.

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Ionisation

When dealing with the Lyman series in the ultraviolet, the transitions are down to the ground state (level 1). The largest transition must represent a fall from the infinite level, ∞, to level 1. Viewed in reverse it can be considered to be equal to the ionisation energy, as this is the energy required to move an electron from the ground state to the infinite level (Note: Ionisation energy is usually expressed per mole of electrons).

Consequently, the ionisation energy may be found by examining the Lyman series at the convergence limit. The wavelength of light corresponding to the convergence limit may be converted to energy using the relationship E = hc/l

This method may be used to find the first ionisation energy of any element.

The wavelength (or wavenumber) values corresponding to the convergence limits are available in data books or in the excellent NIST physics resource.

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Syllabus ref: 2.1

Atoms are the smallest building blocks of matter. There are about 100 naturally occurring types of atom. This chapter explains the ways in which atoms differ from one another.

Understandings

Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons).

Negatively charged electrons occupy the space outside the nucleus.

The mass spectrometer is used to determine the relative atomic mass of an element from its isotopic composition.

Applications and skills

Use of the nuclear symbol notation AZX to deduce the number of protons, neutrons and electrons in atoms and ions.

Calculations involving non-integer relative atomic masses and abundance of isotopes from given data, including mass spectra.

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Mass number

The atomic mass number is represented by the symbol (letter) 'A'. This is not to be confused with the relative atomic mass Ar.

The mass number gives the integral number of nucleons, protons and neutrons found in the nucleus of an atom.

The relative mass is a value that is not necessarily integral that compares a mass to the mass of a carbon isotope, assigned a value of exactly 12.0000 units.

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Atomic number

This is represented by the symbol (letter) 'Z'. It shows us the number of protons in an atom (and the number of electrons in a neutral atom.)

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AZE

Any isotope of any element can be defined by using the A value, the Z value and the element symbol.

Using the values of A and Z it is possible to calculate the number of sub-atomic particles within any specific isotope of an element.

Example: Determine the number and type of sub-atomic particles in the following atom: The atomic number is 1 therefore there is 1 proton and 1 electron The mass number is 3 therefore there are (3-1) = 2 neutrons

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Ions

The system can be extended to cover ions simply by adding the charge onto the element symbol. It is important to remember that a positive ion has LOST electrons.

Example: Determine the number of electrons in the following ion: The atomic number is 12 therefore in a neutral atom there would be 12 protons and 12 electrons. However, the charge is 2+ therefore the atom has LOST 2 electrons The remaining electrons then = 10 electrons

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Worked examples

Q113-01

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Q113-02

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Q113-03

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Q113-04

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Q113-05

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Q113-06

1. 2 protons
2. 18 electrons
3. 21 neutrons
4. 2 electrons

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Q113-07

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Q113-08

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Q113-09

Q113-10

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