Atomic emission spectra

Friday, October 14, 2022 9:41 PM

- On heating atoms of a pure element in gaseous or vapor This experiment was made with an
Hydrogen atom (it is the smallest atom)? :
state to high temperature or exposing them to a low Bec it has one proton and one electron so
pressure inside an electrical discharge tube, they emit The line spectrum was simple
a radiation called emission spectrum (line spectrum)

- When examining this radiation by a device called

"spectroscope", it was found that it is composed of a
limited number of restricted colored lines separated
by dark areas so, it is called line spectrum
-
- The line spectrum is characteristic for each element,
this means there are no two elements with the same
line spectrum, and this is due to the difference in the
atomic number (number of protons) from one element
to another

Whey heating pure elements? :

To get the electrons to be excited
And full on energy

How does light in the first place changes from How does the line spectrum is formed with its
White light into a rainbow when passing through A prism? : characteristic properties? :
ABC Zoom - Refraction: why glass prisms bend and separate light Atomic Spectroscopy Explained

When gas is heated it has heat energy or by electric discharge which makes the
electrons of the atom excited

Getting excited: the need of the electron to absorb energy in order to jump to the
next energy level

And this electron gets its energy from the light source and it takes certain wave
lengths of light
So when the light is shown in a photographic plate it shows missing
frequencies(Absorption)

When the gas emits it light that it has absorbed and reflect it on a photographic
plate it shows the missing frequencies only (emission)

Atomic Structure Page 12

Bohr's atomic model
Friday, October 14, 2022 10:00 PM

- In 1913
- The study of "atomic spectra" is considered the key
which solved the puzzle of the atomic structure. That
was achieved by the Danish scientist "Niels Bohr"

Points that agree with Rutherford's postulates:

- A positively charged nucleus in the center of the atom

- The number of negative electrons (revolve around the

nucleus) = the number of positive protons (inside the
nucleus)

- During the revolving of the electron around the nucleus, a

centrifugal force arises which is equivalent to the
attraction force of the nucleus on the electron

New postulates:

- Stable atom: Is when electrons orbit the nucleus in a rapid

movement without emission or absorption of any amount of
energy

- Electrons orbit the nucleus in definite allowed energy

levels, they cannot be found in the regions between these
levels, where the electron moves from an energy level to
another one via a "complete jump"

- Each electron in the atom has a definite amount of energy

depending on the distance betw its energy level and the
nucleus, the energy of any level increases as its radius
Bec the further away it is from the nucleus (source of attraction)
increases the higher potential energy it has due to its position

- Each energy level is expressed by an integer number called

"The principal quantum number(n)"ant the electron
revolves in the lowest allowed energy level in its ground
state Electrons always seeks stability

- Excited atom: when the electron acquires a quantity of

energy known as "Quantum" by heating or by electric
discharge the electron jumps temporarily to a higher
energy level, this is in case that the absorbed quantum of
energy is equal to the difference in energies betw the two
levels bec it only has to do one complete jump in order not
to be in the forbidden area

- Since the electron in the excited atom is unstable, it

returns back to its original level with emission of the same
Quantum of energy(photon) in the form of radiant light
that appears in the form of a characteristic visible
spectral line of a certain wavelength and frequency in
addition to other invisible lines

- The acquired amount of energy (the quantum) when an

electron transfers from its ground state to the excited
state equals the amount of energy which is released when

Atomic Structure Page 13

 - The acquired amount of energy (the quantum) when an
electron transfers from its ground state to the excited
state equals the amount of energy which is released when
this electron returns back to its ground state level

- A lot of atoms absorb different amounts of energy

(quanta) in the same time that a lot of excited atoms
release other quanta producing spectral lines, these
spectral lines indicate the energy levels from which their
electrons are transmitted back to the ground state

Notes:
The line spectrum of hydrogen atom which consists of four
colored lines indicating the higher energy levels from
which the electrons transfer to the second energy level
only Visible light is when it has an average
wavelength
That s why we can see visible light at the
The amount of energy required to transfer an electron second energy level because it is considered
betw the different energy levels are not equal, bec the the level when middle length wavelengths
are emitted or absorbed
distance and the difference in energy betw them are not
equal

The quantum required to transfer an electron from an Invisible light are that who has
energy level to another decreases as we go farther from Either
Long wavelength or short wavelength
the nucleus, bec the energy gap decreases, as we go
farther from the nucleus

The advantages (success) of Bohr's atomic model:

- It explained the hydrogen spectral lines

- It introduces the idea of quantized energy to determine

the electron energy in different energy levels in the atom

The Drawbacks of Bohr's atomic model:

- It failed to explain the spectrum of any other element,

except hydrogen atom which is the simplest electronic
system, where it contains one electron only

- It considered the electron as a negative charged particle

only and ignored its wave prop.

- It presumed that it is possible to determine precisely

both the location and speed of an electron at the same
time, but in fact this is experimentally impossible

- It described the electron as a particle moving in a circular

planar orbit, this means that hydrogen atom is planar.
Later on, it was probed that the hydrogen atom has three
dimensional coordinates

Atomic Structure Page 14

Modern atomic theory (Modified Bohr's model)
Saturday, October 15, 2022 9:33 PM

The Modifications On Bohr's model:

- The dual nature of electron

- The Heisenberg uncertainty principle
- The wave-mechanical theory of the atom

Atomic Structure Page 15

 - The dual nature of electron
Saturday, October 15, 2022 9:40 PM

All the previously mentioned theories considered the De Broglie

electron just as a tiny negatively charged particle.

However, all experimental data showed that the electron

has a dual nature, as it is a material particle which also
has wave properties

The dual nature of electron :

the electron is a material particle which has wave
properties

Atomic Structure Page 16

 - The Heisenberg uncertainty principle
Saturday, October 15, 2022 9:44 PM
Heisenberg

The determination of both the velocity and position of an

electron at the same time is practically impossible so to
speak in terms "probability"

This is because the electron wave motion doesn't have a

certain location

Heisenberg uncertainty principle:

The determination of both the velocity and position of an

electron at the same time is practically impossible and this
is subjected to the laws of probability

Atomic Structure Page 17

 - The wave-mechanical theory of the atom
Saturday, October 15, 2022 9:53 PM

Schrodinger
In 1926 Schrodinger applied the ideas of
Planck, Einstein, De Broglie and Heisenberg

- He established the wave-mechanical theory of atom

- Derive a wave equation that could be applied to the
electron movement in the atom

On solving the Schrodinger's equation, it is possible to :

- Determine the allowed energy levels

- Define the regions of space around the nucleus, where it is

most probable to find the electron in each energy level

The wave-mechanical theory:

Changed our concept about the movement of electron
where instead of having forbidden for the electron, this
theory introduced the concept of "Electron Cloud" and
"Orbital"

Electron Cloud:
It is the region of space around the nucleus, in which
the electron probably exists in all directions and
distances (dimensions) -region A

Orbital:
It is the region within the electron cloud which has
high probability of finding the electron -region B

Atomic Structure Page 18

*Summary
Sunday, October 16, 2022 11:56 AM

Atomic model Dalton Thomson Rutherford Bohr Modern atomic theory

Atom - Solid indivisible - A solid sphere - contains a vast - contains a vast - contains a vast
Particle space(not solid) space(not solid) space(not solid)
- is of uniform positive
- Atoms in the same electric charges in - Electrically neutral - Electrically neutral - Electrically neutral
element have which a number of
similar masses negatively charged - Planar (2D)
But they differ electrons is embedded
from one element to to make the atom
another electrically neutral

Nucleus ----- ----- - Positively charged - Positively charged - Positively charged

- Smaller than atom - Smaller than atom - Smaller than atom

- Has most of the - Has most of the - Has most of the

atomic mass atomic mass atomic mass
Electrons ----- - Negatively charged - Negatively charged - Negatively charged material - Dual nature of the electron
particles Bec it's material particles have
- Are embedded in the - There total negative wave prop
atom charge = to positive - The energy of electron incr.
charge of the nucleus as distance form the nucleus - Uncertainty principle
(radius of energy level) incr.
- They move around the
nucleus in tremendous - They orbit the nucleus in - The region around the nucleus in
speeds in special orbits definite orbits, and can not which the electron probably exists
be found in spaces between in all dimensions is called electron
- There have negligible these orbits(forbidden area) cloud
mass compared to nucleus
- When electron gains a - The 3D region of space that
quantum of energy it jumps indicates where there is a high
to higher energy level, and probability of finding an electron
the stable becomes excited in known as the orbital
Additional Compound: ----- This theory could not This theory could not explain ------
information The atoms of explain the system of the line spectrum of any
different elements revolving the electrons element atom other than
combine with each around the nucleus hydrogen atom
other in simple
numerical ratios
forming compound

Atomic Structure Page 19