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Chapter I Atomistic-Chemical Liaison

I.1.Description (for the hydrogen atom) To resolve the above contradictions, Bohr proposed four hypotheses: In the atom, the nucleus is immobile while the electron of mass m moves around the nucleus in a circular orbit of radius r.Atomic mass The atomic mass is equal to the sum of the masses of the constituents of the atom: mat = Zme + Zmp + Nmn (kg) The use of this unit is inconvenient, so chemical units that are easier to handle have been chosen; the reference term being carbon 12.Bohr model This model only applies to monoelectronic atoms, i.e. the hydrogen atom and hydrogenoids, i.e. ions with only one electron (He+, Li2+ ...).Nucleus The nucleus contains two types of massive particles; The proton has a charge of +1.60.10-19 C (coulombs), which corresponds to the elementary charge for a mass of 1.673.10-27 kg.

• The neutron, on the other hand, has a zero charge and a mass of 1.675.10- 27kg.An atom is an electrically neutral unit with a central part, the nucleus (protons + neutrons), where practically all its mass is centered, and around which are electrons.It is always written with a capital letter, eventually followed by a small letter:

Z is called the atomic or charge number and denotes the number of protons (it is also the number of electrons for a neutral atom).Relative atomic mass In the general case, an element has one or more isotopes, so the atomic mass is the sum of the proportions of each isotope.Mole and molar mass On our scale, we reason in terms of a certain quantity of matter called a mole: A mole is the quantity of matter containing as many atoms as there are in 12g of carbon 12.Definitions

Matter is formed from elementary grains: atoms.Neutrons and protons make up an atomic nucleus, which is held together by the strong interaction between them.A is called the atomic mass number and denotes the number of nucleons (protons + neutrons).Isotopes These are atoms with the same atomic number Z but different mass numbers A. An element may have one or more isotopes.1023 By definition: One mole of carbon-12 atoms weighs 12g.Electrons occupy space in matter.I.1.2.

Chapter I
Atomistic-Chemical Liaison

I.1. Atomistic
I.1.1. Definitions

Matter is formed from elementary grains: atoms. An atom is an electrically neutral unit with a central part, the nucleus (protons + neutrons), where practically all its mass is centered, and around which are electrons.

I.1.2. Nucleus
The nucleus contains two types of massive particles;
The proton has a charge of +1.60.10-19 C (coulombs), which corresponds to the elementary charge for a mass of 1.673.10-27 kg.

• The neutron, on the other hand, has a zero charge and a mass of 1.675.10- 27kg. So we can see that protons and neutrons have a similar mass but a completely different charge. The atomic nucleus therefore has a positive charge. Neutrons and protons make up an atomic nucleus, which is held together by the strong interaction between them.

I.1.3. Electronic nuance
It corresponds to all electrons. An electron has a charge of -1.60. 10-19 C and a mass of 0.911.10-30 kg. An electron is 1800 times lighter than a proton. It has a negative charge opposite that of the proton. An atom has as many electrons as protons, so its overall charge is zero. The universe has the same number of electrons as protons. Electrons occupy space in matter. The nucleus is mostly made of mass.
I.1.4. Identification of elements
I.1.4.1. Representation
Each chemical element has its own symbol. It is always written with a capital letter, eventually followed by a small letter:

Z is called the atomic or charge number and denotes the number of protons (it is also the number of electrons for a neutral atom). For each element, the charge of the nucleus (protons) is +Ze. Similarly, the charge of the electrons is -Ze. A is called the atomic mass number and denotes the number of nucleons (protons + neutrons).
If N is the number of neutrons, the relationship is A = Z + N
I.1.4.2. Isotopes
These are atoms with the same atomic number Z but different mass numbers A. An element may have one or more isotopes. It is not possible to separate them by chemical reactions, but this can be done using physical techniques, in particular mass spectroscopy.

I.1.4.3. Atomic mass
The atomic mass is equal to the sum of the masses of the constituents of the atom:
mat = Zme + Zmp + Nmn (kg)
The use of this unit is inconvenient, so chemical units that are easier to handle have been chosen; the reference term being carbon 12.
By definition, the unit of atomic mass is (𝟏/𝟏𝟐)th of the mass of an atom of carbon 12 (12C).
I.1.4.4. Mole and molar mass
On our scale, we reason in terms of a certain quantity of matter called a mole: A mole is the quantity of matter containing as many atoms as there are in 12g of carbon 12. This number is called Avogadro's number N: = 6.023. 1023
By definition: One mole of carbon-12 atoms weighs 12g. The mass of an atom is 12 a.m.u., so:

12 g = N. 12 a.m.u

Ou encore
1 a.m.u = 1/N = 1,66 . 10-24 g =1,66 . 10-27 kg.

I.1.4.5. Molar mass
The mass of one mole of atoms of an element is called the molar mass of the atom.

I.1.4.6. Relative atomic mass
In the general case, an element has one or more isotopes, so the atomic mass is the sum of the proportions of each isotope.
m = Σ (xi. mi) a.m.u
Similarly, the molar mass will be:

M = Σ (xi. Mi) (g/mole)

I.1.5. Classical atomic models
I.1.51. Rutherford's model
Also called the planetary model because the positive nucleus represents the sun and the electrons describe orbits around the nucleus like planets around the sun.
The mechanical stability results from the compensation of the attractive forces Fa by the centrifugal forces Fc due to the rotation of the electrons around the nucleus.
The advantage of this model is that it uses only the laws of classical mechanics.
However, it does have its inconveniences:
Electromagnetic theory requires the electron to radiate electromagnetic waves, so it will lose energy and end up falling on the nucleus.
The light energy emitted varies continuously.
These two conclusions contradict experiment.

I.1.5.2. Bohr model
This model only applies to monoelectronic atoms, i.e. the hydrogen atom and hydrogenoids, i.e. ions with only one electron (He+, Li2+ ...).

I.1.5.2.1. Description (for the hydrogen atom)
To resolve the above contradictions, Bohr proposed four hypotheses:
In the atom, the nucleus is immobile while the electron of mass m moves around the nucleus in a circular orbit of radius r.