الباب الاول للغات مراجعةشرح د/ عاطف خليفة

[عاطف خليفة]

ATOMIC STRUCTURE

* (1) Rutherford’s Atom:

A)The atomIt is very small, in size it has complicated structure like sun around which electrons ( plants)orbit.

The nucleus Most of the atomic mass and positive charge are concentrated in the nucleus.

C)The electrons
1- They have negligible mass
2- the sum of electrons (negative charges) equals the number of positive charges (protons).
3- The attraction force of it overcome by another force that equals it in quantity and opposes it in direction namely centrifugal force.

* Objections on Rutherford’s atomic model
It was contradicted by Maxwell’s theory
Maxwell’s theory states that when an electric charged particle moves in an orbit it will lose its energy gradually by radiation and its radius orbit decreases.
By applying this theory on Rutherford’s model, the electrons will lose their energies gradually, their state continuous emission of radiation W consequal gradual decrease in the orbital vadius ,orbits decrease and they spiral inwards until they hit the nucleus.

[عاطف خليفة]

* (2) Bohr’s atomic model

Bohr’s Postulates

1- He adopted some of Rutherford’s postulates

2- He added that; the electrons orbit the nucleus without emission or absorption any energy.

3- The electrons orbit only in definite allowed energy level

4- The energy of any level increases as its radius increases.

5- Each energy level is expressed by a whole number (Principal quantum number) - which is 1 for level K-, 2 for level L, ..

6- When an electron acquires an amount of energy (quantum) by heating or electric discharge, it becomes excited and it jumps to higher energy level , then it returns to its original level losing the temporarily absorbed energy in the form of radiant.

7- Many atoms absorb different amount of energies and others radiate energies at the same time

* Notes

1. Quantum : The amount of energy absorbed or emitted when an electron jumps from one level to another

2. The amount of energies needed to transfer the electron through different energy levels are not equal.

3. The electron can’t orbit in the distance between energy levels

4. There is no parts of quantum

* Bohr’s model succeeded in

(1) Explaining the hydrogen atom spectrum

(2) Introducing the idea of quantized energy states for electron
(3) Reconciliation between Rutherford and Maxwell theories.

* Bohr’s model failed in

(1) The model failed to explain the spectrum of any other element expect hydrogen.

(2) It didn’t consider the wave properties of the electron

(3) It is impossible to determine precisely both the location and the
speed of an electron at the same time

(4) It considered that the atom is planar while it has three dimensional coordinates

[عاطف خليفة]

The Principles of Modern Atomic Theory

* I) The dual nature of the electron
1. The electron is a material particle with wave properties

2. The matter wave motion differ from electromagnetic waves in that they are not separated from the moving body and its speed doesn’t equal light speed.

3. The length of waves associated with the motion of minute particles (such as electron) could be experimentally measured.

* II) The Heisenberg uncertainty principle:
1. The determination of both velocity and position of an electron at the same time is practically impossible

2. It is probable to locate the electron in this or that place (the probability is more precise).

* III) The wave equation (Schrodinger)

1. Schrodinger put a wave equation that could describe the electron wave motion in the atom.

2. Electron cloud is used to describe any orbital

3. Orbital is used to identify region of space around the nucleus in which the electron most probable exists.

[عاطف خليفة]

Quantum numbers

They define the orbital, energy, shape and the direction of orbital

* I) The principal quantum number (n)

1- It is used to define the order of the principal energy level

2- The number of electrons required to fill an energy level= ( 2n2 )
It is limited to any whole number value
e.g. 1,2,3,…,7.

Ex
The 1st shell is filled with (2×12)=2electrons
The 2nd shell is filled with (2×22)=8electrons

* II) The subsidiary quantum number (l)

1. It indicates the number of energy sublevels within each principal energy level

2. Each principal energy level consists of a number of energy sublevels equal to its principal quantum number

3. Sublevels are designated as s.p.d and f.

4. sublevels are arranged according to increasing energy as following order :
S< P < d< f.


Note
Sommerfield found that each one spectral line was made of some spectral lines.

* Ill) The magnetic quantum number (m)

1. It represents the number of orbitals within a certain energy sublevel

2. Sublevel(s) has one orbital of spherical symmetrical

3. Sublevel (p) has three orbitals their axises take the three spatial formations(px - py - pz )
The electron cloud of each orbital is dumb-bell shaped

4. Sublevel (d) has 5 orbitals

5.Sublevel (f) has 7 orbitals

* IV) The spin quantum number (ms)

- It defines the type of spin motion of the electron around its axis

- The electron spins in clock-wise ↑ or anticlockwise ↓



* The relationship between n, I and m

Fig
1. The number of sublevels equals the number of the principal level (n)

2. The number of orbitals within a principal level equals (n2)

3. The maximum number of electrons can be found in a principal level equals 2 n2

[عاطف خليفة]

Principals of distributing electrons

* I) Auf-bau (building - up) principle.

1. Electrons occupy the orbitals in the order of increasing orbital energy the lowest energy orbitals are filled first

2. The sequence of energy sublevels as follows :-
1s < 2s < 2p< 3s < 3 p < 4S < 3d < 4p < 5S < 4d
< 5p < 6s <4f < 5d < …

II) Hund’s rule

• No electron pairing takes place in a given sublevel until each orbital contains one electron

• The spin of single electrons is in the same direction

• It is preferable for an electron to be paired with another one in a lower energy level than to jump to a higher energy level

Ex
N=7 , O = 8The distribution may be:
1) 2,5 according to principal levels
2) 1 s2 , 2s2 , 2p3 according to Auf-bau principal.
3) 1 s2, 2s2 , 2Px1 , 2Py1 2Pz1 according to Hund’s law.

[عاطف خليفة]

SUMMARY

Quantum

It is the amount of energy absorbed or emitted when an electron jumps from one energy level to another

The Dual nature of the electron

It means that the electron is a particle and it has wave properties

Uncertainty Principle (Probability)

- It is impossible to determine both the location and the velocity, of the electron precisely at the same time

- It is probable to locate the electron in this or that place

The Electron Cloud (Orbital)

It is the region of space around the nucleus where is a great probability of finding the electron.

Quantum Numbers

They define the energy, shape and direction of orbitals

The principle quantum number

It defines the principle energy level and the number of electrons which can occupy a given principal energy level

The subsidiary quantum number (Orbital or ozimuthal)

- It defines the energy sublevels
- The number of sublevels equals the number of the principal level to which these sublevels belong

The magnetic quantum number
It defines the orbitals of a given energy sublevel and their directions .

The spin quantum number

It describes the spin motion of an electron around its own axis
clockwise or anti-clockwise).

The auf-bau principle

Electrons occupy the orbitals in the order of increasing orbital energy. the lowest energy orbitals are filled first.

Hund’s rule
No electron pairing takes place in a given sublevel until each orbital contains one electron