Chemistry 01 - Chapter 1 - Basic Concepts PDF

***Chemistry01*** **CHAPTER I: BASIC CONCEPTS** **1. INTRODUCTION** Matter is anything that possesses mass and occupies space. All objects - air, water, oil, etc. - are matter, or bodies. These bodies can exist in different forms, called physical states: they can be solid, liquid or gaseous, depe...

***Chemistry01*** **CHAPTER I: BASIC CONCEPTS** **1. INTRODUCTION** Matter is anything that possesses mass and occupies space. All objects - air, water, oil, etc. - are matter, or bodies. These bodies can exist in different forms, called physical states: they can be solid, liquid or gaseous, depending on the degree of cohesion of the molecules that make them up. 2\. HISTORY OF THE ATOM Since ancient times, the problem of the nature (aspect) of matter has been posed: is it continuous or discontinuous? -5 ^th^ century B.C. (Greece) Democritus imagines that matter is made up of small, indivisible and inseparable particles, which he calls \"atoms\". -4 ^th^ century BC (Greece) Aristotle asserts that matter is made up of 4 elements (fire, air, earth and water). This theory prevailed for almost 20 centuries! -In 1805, John Dalthon (England) revived the idea of atoms to explain proportions. J.J.THOMSON \'1897 (U.K.) proves that some rays are made up of negatively-charged particles known as electrons. He measured the m/e ratio and gave the first model of the atom (The atom would be a positively-charged \"paste\" containing negatively-charged grains (electrons).). -In 1910, Rutherford formulated a new theory on the structure of the atom. According to him, the atom has a lacunar structure, a central spherical nucleus (dense and compact) with a diameter of the order of 10^-14^ m, made up of particles with (+)charges: protons. Around the nucleus gravitate particles with (-) charges: electrons, giving the atom a diameter of the order of 10^-10^ m (planetary model). Later, physicist J. Chadwick (1932) confirmed the existence of a third particle: the neutron, with its neutral charge. -In 1913, Bohr proposed a layered atomic model to explain the hydrogen spectrum. -In 1925, SCHRODINGER, HEISENBERG and DE BROGLIE invented (formulated) the theory of quantum mechanics. This theory establishes that electrons have no definite orbit, but makes it possible to determine their \"probability of presence\" around the nucleus. 3\. REMINDER OF THE ATOMIC MODEL 3.1 Composition of the atom Matter is made up of atoms, themselves consisting of a nucleus surrounded by an electron cloud (figure 1. and table 1.). The central spherical nucleus is made up of A nucleons, divided into : Z protons (charge q = + e; mass m~p~) and N neutrons (charge q = 0; mass m~n~).  **Fig I.1.** Vue schématique de la structure de la matière The electron cloud of a neutral atom is made up of Z electrons (charge q=-e; me\