University “POLITEHNICA” of Timisoara Faculty of Industrial Chemistry and Environmental Engineering

1. University “POLITEHNICA” of Timisoara Faculty of Industrial Chemistry and Environmental Engineering GENERAL CHEMISTRY Assoc.Prof. dr.eng. Andrea Kellenberger

2. GENERAL CHEMISTRY COURSE Lecture: 2h / week Laboratory: 2h / week Evaluation form: Examination Nr. of credits: 5

3. Chapter 1 INTRODUCTION

4. Space Universe Substance Matter Energy

5. Einstein’s equation: E = mc2 E – energy, in J m – mass, in kg c – light speed, in m s-1

6. Substance is what all things consists of. One of the most important properties of the substance is the mass. Other characteristics of the substances are homogeneity and constant composition. Homogeneity = same characteristics in all the volume. Constant composition = in any given portion of a substance there are the same particles which interact in the same way. Examples of substances: water, sugar, oxygen, sodium chloride, copper, hydrochloric acid, sodium hydroxide.

7. The great majority of things consist of a mixture of substances. The air, for example, is not a substance, because it can be separated through distillation in oxygen, nitrogen, argon and other gases. The petrol is not a substance as well – through distillation it can be separated in hydrocarbons. Chemistry is the science of substances. Chemistry studies the structure, properties and changesof substances.

8. International System of Units ( Sİ units) (from French: Le Systeme İnternational d’Unites). Making observations is a key part of the scientific process. Sometimes observations are qualitative, for example: the substance is a green gas, and sometimes they are quantitative (the mass is 10 grams, the temperature is 25ºC or the pressure is 1015 mbars). A quantitative observation is called a measurement. A measurement always consists of two parts: a number and a unit.

9. Table 1. Sİ Fundamental Units

10. Table 2. Sİ Derived Units

11. Examples: - for volume (liter, L: 1L= 1dm3), for pressure (bar: 1 bar = 105 Pa); - for temperature, there are two non SI scales: Celsius (ºC) and Fahrenheit (ºF). Temperature conversions can be made using the equations shown below: Kelvin from Celsius: T (K)= t (ºC) + 273.15 Celsius from Fahrenheit: t (ºC )= 5/9 [t(ºF) – 32]

12. CHAPTER 2 ATOMIC STRUCTURE OF THE SUBSTANCES

13. One of the oldest scientific concepts is that all matter can be broken down until finally the smallest possible particles are reached; these particles cannot be further subdivided. The Greek philosopher Democritus (460 – 370 B.C.) considered these particles to be in a constant motion, but able to fit together into stable combination. The characteristics of substances resulted from the different size, shape and arrangements of the particles, named atoms. In Greek, atom means indivisible.

14. Modern atomic theory was developed by John Dalton (1776 – 1844), based on quantitative data, not only qualitative observations or speculations. Two natural laws serve as the basics of Dalton’s atomic theory: • Law of conservation of mass • Law of definite composition (proportions):

15. a.Law of conservation of mass: The total mass of materials present after a chemical reaction is the same as before the reaction. Example: the reaction between Mg and O2. 0.24g Mg react with 0.16g oxygen. After the reaction, 0.40g MgO (magnezium oxide) were obtained. b.Law of definite composition (proportions): All samples of a compound have the same composition, the same proportions by mass of the constituent elements.

16. Fe S To see how the law of constant composition works, let’s consider the compound FeS (iron sulfide). A sample of 10g FeS contains 6.36g Fe and 3.64g S. That means: and

17. Fe S Another sample of 25g FeS contains 15.91g Fe and 9.09g S. The composition of the second sample is the same : and

18. J. Dalton was aware of these observations and he offered an explanation for them. This is known as Dalton’s atomic theory. The main ideas of this theory can be stated as follows : • Chemical elements are made of small particles called atoms. • All atoms of a given element are identical. • The atoms of a given element are different from those of any other element.

19. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative number and type of atoms. • Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.

20. In order to apply Dalton’s theory in predicting new phenomena, it was necessary to assign characteristic masses to atoms. These masses became known as atomic weights. Since they are very small, it is impossible to isolate and weigh individual atoms. Dalton tried to establish relative atomic weights. If an atom of hydrogen, for example, is taken to have the mass of 1 unit, the mass of oxygen atom is 16.

21. 2.1. Atom structure At the end of the 19th century, the English physicist J. J. Thomson showed that the atoms of any element emit tiny negative particles. Thus, he concluded that all types of atoms must contain these negative particles called electrons. Although atoms contain negative particles, the whole atom is not negatively or positively charged. So, Thomson concluded that the atom must also contain positive particles that balance the negative charge given by the electrons. He imagined the “plum pudding model” of the atom, in which electrons are scattered like plums into the uniform “pudding” of positive charges.

22. Rutherford’s experiment Rutherford measured the deviation of alpha particles (helium ions with a positive charge) directed normally onto a sheet of very thin gold foil. Assuming the plum pudding model, the alpha particles should all have been deviated by, at most, a few degrees. The results of the experiment were very different from those Rutherford anticipated. Most of the α particles passed straight through the foil, some of them were deflected at large angles and some were even reflected backward.

23. Rutherford’s experiment

24. Conclusions: • the plum pudding model for the atom could not be correct; • the atom must contain a very small (compared with the size of the atom) positive charge which causes the large deflections of the α particles; • the atom is mostly empty space because most of the α particles past directly through the foil.

25. These results could be explained only in terms of nuclear atom: an atom with a dense center of positive charge (nucleus) around which tiny electrons moved in a space otherwise empty. He concluded that the nucleus has a positive charge to balance the negative charge of the electrons and that it must be small and dense. This picture of the atom was the planetary model of the atom.

26. Planetary model of the atom

27. In 1919 Rutherford discovered that the nucleus contains positive particles named protons. Furthermore, in 1932, James Chadwick discovered that nucleus contains also neutral particles – neutrons. Protons and neutrons are known as nucleons. Electrons, protons and neutrons are fundamental particles of the matter. There are more than 30 other fundamental particles. Properties of the main fundamental particles are given in the next table.

28. Properties of the main fundamental particles

29. The attraction force between the positive charges (protons) and the negative ones (electrons) keeps the atom together. In this image the nucleus is like a sun and electrons like planets. Several problems arise with this concept – the electrons might be expected to slow down gradually and fall on the nucleus? • To explain why this did not occur, Niels Bohr (1913) postulated: • The electrons can move around the nucleus only on certain orbits (allowed orbits).

30. The electrons can gain or lose energy only by jumping from one allowed orbit to another. When an electron moves towards the nucleus energy is radiated and if it moves away from the nucleus energy is absorbed. • For an electron to remain in its orbit the electrostatic attraction force between the electron and the nucleus must equal to the centrifugal force which tends to throw the electron out of its orbit. N. Bohr admitted that the orbits of the electrons are circular.

31. Bohr’s model of the atom

32. A. Sommerfeld (1916), based on the atomic spectra of hydrogen, suggested that the permissive orbits of the electrons may be elliptic. Bohr – Sommerfeld model of the atom

33. Atomic number, mass number and chemical element The number of protons in an atom is called the atomic number Z. In an atom, which must be electrically neutral, the number of electrons are also equal to Z. The total number of protons and neutrons in an atom is the mass number A. Thus, the number of neutrons is A-Z. The three subatomic particles considered, the electron, proton and neutron, are the only ones involved in chemical phenomena. A study of matter at its most fundamental level must consider a lot of additional subatomic particles.

34. All atoms with the same number of protons signify a chemical element. Each element has a name and a distinctive symbol. Chemical symbols are one or two letter abbreviations of the elements name (usually the Latin name). The first letter, but never the second is capitalized. For example :

36. mass number symbol of the element atomic number To represent the composition of any particular atom, we need to specify its number of protons, neutrons and electrons. We can do this with the symbol : Atoms that have the same atomic number Z, but different mass numbers A are called isotopes.

37. The most simple element is hydrogen. The nucleus of hydrogen consists only of one proton. Consequently, the hydrogen atom has just one electron. This is isotope called light hydrogen : . Deuterium (heavy hydrogen): or D. Tritium (super-heavy hydrogen): or T. - 0.015% - 99.985% - insignificant percent Hydrogen has as well another two isotopes : Natural abundance of hydrogen isotopes is :

38. Abundance of the elements What is the most abundant element? This simple question does not have a simple answer. If we consider the entire Universe, hydrogen accounts for about 90% of all the atoms and 75% of the mass, and helium accounts for most of the rest. If we consider only the elements present on Earth, iron is probably the most abundant element. However, most of the iron is in Earth’s core. The currently accessible elements are those present in Earth’s atmosphere, oceans and solid continental crust up to 16 km depth. The relative abundance in these parts of the Earth are called Clark parameters.

40. Not all the known elements exist in Earth’s crust. There are only 88 natural elements. The rest of known elements can be produced only artificially by nuclear processes. Moreover, most of the elements do not occur free in nature, that is, as uncombined element. Only about 20% of them do. The remaining elements occur in chemical combinations with other elements. We can see in the last table that oxygen is the most abundant element in the Earth’s crust (49.4%).

41. - 99.759% - 0.037% - 0.204% There are 3 natural isotopes of oxygen: Large amount of oxygen exists in water and rocks as well in free state like molecular oxygen (O2) and ozone (O3). Molecular oxygen (O2) and ozone (O3) are allotropes of the element oxygen. The second element in Clark’s table is silicon (Si – 25.75%), but silicon occurs only in chemical combinations.

42. 1 amu is the 12th part of the mass of the isotope Atomic mass unit Because the fundamental particles and the atoms are very tiny it is difficult to operate with the small values of their masses. This is the reason why the atomic mass unit (amu) was introduced. 1 amu = 1.66 · 10-27 kg Generally, atomic masses of the elements are fractional number because the natural elements are a mixture of two or more isotopes.

43. For example, magnesium has 3 stable isotopes: (78,70 %), exact atomic mass: 23,98504 (10,13 %), exact atomic mass: 24,98384 (11,17 %), exact atomic mass : 25,98259 Knowing the abundance of the stable isotopes one may calculate the atomic mass of magnesium: AMg=0.787 x 23.98504 + 0.1013 x 24.98384 + 0.1117 x 25.98259 = = 24.30934

44. Electronic configuration of the atoms Louis de Broglie (France) and Werner Schrödinger (Austria) in the mid 1920s, suggested that like a light, the electron has both a wave and particle properties. When Schrödinger carried out a mathematical analysis based on this idea, he obtained a new model for the atom: wave model. In this model the electron has not a well defined orbit. The motion of the electron seems to be rather a vibration. The three-dimensional region of space around the nucleus in which we can find the electron is called orbital. In fact, it is a region of probability where the electron is likely to be found.

45. Let us consider a multi electronic atom. We can assume that each electron has a specific mean path from nucleus. The electrons having a similar mean path form a main energeticlevel or main electronic shell, characterized by theprincipal quantum number n. The main shells are denoted by letters. The first main shell is the nearest level to the nucleus and it has a minimum energy.

46. K shell (n = 1) consists of one s sublevel, containing one orbital with a spherical symmetry named s orbital: s orbital

47. L shell (n = 2) has 2 sublevels: one s sublevel containing one spherical shaped s orbital and one p sublevel containing 3p orbitals. Each p orbital consists in two lobes distributed along one of the three rectangular axes through the nucleus:

48. In order to characterize the shape of the orbital the orbital quantum number or azimuthal numberl has been introduced. For s orbital l= 0 and for p orbital l= 1. All orbitals having the same l value form a subshell or sublevel. The orientation of the orbitals is given by the magnetic quantum number m. It may be 0; ±1; ±2; …; ±l. For example, if l = 1 provided that m = -1; 0; +1, that is there are 3 p orbitals: px, py and pz.

49. For the third electronic level M (n = 3), the values of the orbital and magnetic numbers are the following: Beside s and p orbital, on the third electronic level there are 5 orbitals characterized by orbital number l = 2, named d orbital. There are 5 different d orbitals:

50. The d orbitals