atomic emission spectra Flashcards
what is emission spectrum ( line spectrum )?
heating atoms of a pure element- in gaseous or vapor state- to high temperatures or exposing them to a low pressure inside an electrical discharge tube
device to examine this radiant light
spectroscope
why is it called line spectrum?
because it is composed of limited number of restricted coloured lines separated by dark areas
why is the line spectrum a defining characteristic for each element?
because there are. no two elements with the same line spectrum, and this is due to the difference in the atomic number from one element to another
what was the element that emitted the line spectrum and how many colours appeared ?
hydrogen, four colours
Violet Blue Green Red
Bohr’s atomic model
atomic spectra is considered the key which solved the puzzle of the atomic structure
Bohr’s postulates
(points that agree with Rutherford’s postulates)
1.a positively charged nucleus exists in the center of the atom
2.the number of negative electrons equals the number of positive protons inside the nucleus
3.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
Bohr’s new postulates
what is a stable atom?
is the state of atom when its electrons energy is the least
Bohr’s new postulates
what does the electrons orbit the nucleus in?
definite allowed energy levels
Bohr’s new postulates
what is a complete jump?
electrons move from an energy level to another via complete jump
Bohr’s new postulates
what is the principle quantum number?
each energy level is expressed by an integer number called the principle quantum number and the electron revolves in the lowest allowed energy level in its ground state
Bohr’s new postulates
what does the definite allowed energy depend on?
the distance between its energy level and the nucleus
Bohr’s new postulates
what happens to the energy level when its radius increases?
the energy of any level increases as its radius increases
Bohr’s new postulates
what is a quantum?
is a quantity of energy gained or lost when the electron is transferred from an energy level to another energy level
Bohr’s new postulates
what happens to the electron when it gains energy?
the electron jumps temporarily to a higher energy level
Bohr’s new postulates
what is an excited atom?
is the state of the atom after gaining a quantum of energy, through heating or electrical discharge
why is the amount of energy required to transfer an electron between the different energy levels are not equal?
because the distance and the difference in energy between them are not equal
why does the quanta required to transfer an electron from an energy level to another decreases as we go farther from the nucleus?
because the energy gap decreases as we go farther from the nucleus
what happened despite the great efforts of Bohr to formulate his atomic model?
the quantitive calculations of his theory didn’t match all the experimental results
advantages of Bohr’s atomic model
1) it explained the hydrogen spectral lines
2) it introduced the idea of quantized energy to determine the electron energy in different energy levels in the atom
drawbacks of Bohr’s atomic model
1) it failed to explain the spectrum of any other element except hydrogen which is the simplest electronic system, where is contains one electron only
2) it considered the electron as a negative charged particle only and ignored its wave properties
3)it presumed that it is possible to determine precisely both location and speed of the electron at the same time
4)it described the electron as a particle moving in a circular planar orbit, later was proved that the hydrogen atom has three dimensional coordinates
the dual nature of electron
the electron is a material particle which has wave properties
Heisenberg’s 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
Schrödinger’s equation
1) Determine the allowed energy levels
2)define the regions of space around the nucleus, where it is probable to find the electron in each energy level
