Principle of Inorganic Chemistry for 1st Class By Dr. Khalil K. Abid Department of Chemistry , College of Science University of Mustansiriyah, Baghdad – IRAQ Email: [email protected]; [email protected] 1 Introduction What Inorganic Chemistry means? Inorganic chemistry is the study of the synthesis and behavior of inorganic and organometallic compounds. This field covers all chemical compounds except the organic compounds (carbon based compounds, usually containing C – H bonds), which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, and there is much overlap, most importantly in the sub-discipline of organometallic chemistry. It has applications in every aspect of the chemical industry–including catalysis, materials science, pigments, surfactants, coatings, medicine, fuel, and agriculture. Chemistry deals more with the changes that can be effected in materials. One of the most important early reactions was the reduction of metal oxides, carbonates, and sulfides to the free metals: 2Cu (OH) .CO + 2C ---+ 4Cu + 4CO + 2H O 2 2 3 2 2 Fe O + 2C ---+ 3Fe + 2CO 3 4 2 This was the first example of applied redox chemistry, but to this day the gain and loss of electrons is central to inorganic chemistry Simple inorganic compounds: Many inorganic compounds are characterized by high melting points. Inorganic salts typically are poor conductors in the solid state. Other important features include their solubility. Inorganic compounds are found in nature as minerals. Soil may contain iron sulfide as pyrite or calcium sulfate as gypsum. Inorganic compounds are also found multitasking as biomolecules. The first important man-made inorganic compound was ammonium nitrate for soil fertilization through the Haber process. Inorganic compounds are synthesized for use as catalysts such as vanadium(V) oxide and titanium(III) chloride, or as reagents in organic chemistry such as lithium aluminium hydride. Subdivisions of inorganic chemistry are organometallic chemistry, cluster chemistry and bioinorganic chemistry. These fields are active areas of research in inorganic chemistry, aimed toward new catalysis, superconductors and therapies. Organometallic compounds: Usually, organometallic compounds are considered to contain the M-C-H group. The metal (M) in these species can either be a main group element or a transition metal. Examples: Fe (CO) , B H , [Mo Cl ]2−, 4Fe-4S. 3 12 10 14 6 14 2 Bioinorganic compounds: By definition, these compounds occur in nature, but the subfield includes anthropogenic species, such as pollutants (e.g., methylmercury) and drugs (e.g., Cisplatin). The field, which incorporates many aspects of biochemistry, includes many kinds of compounds, e.g., the phosphates in DNA, and also metal complexes containing ligands that range from biological macromolecules, (e.g., coordinated to gadolinium complexes employed for MRI). Traditionally bioinorganic chemistry focuses on electron- and energy-transfer in proteins relevant to respiration. Medicinal inorganic chemistry includes the study of both non-essential andessential elements with applications to diagnosis and therapies. • Examples: hemoglobin, carboxypeptidase. Solid state compounds: This important area focuses on structure, bonding, and the physical properties of materials. In practice, solid state inorganic chemistry uses techniques such as crystallography to gain an understanding of the properties that result from collective interactions between the subunits of the solid. Included in solid state chemistry are metals and their alloys or intermetallic derivatives. Related fields are mineralogy and material science. Examples: silicon chips, zeolites. Theoretical inorganic chemistry: An alternative perspective on the area of inorganic chemistry begins with the Bohr model of the atom and, using the tools and models of theoretical chemistry and computational chemistry expands into bonding in simple and then more complex molecules. Precise quantum mechanical descriptions for multielectron species, the province of inorganic chemistry, is difficult. This challenge has spawned many semi-quantitative or semi-empirical approaches including molecular orbital theory and ligand field theory, In parallel with these theoretical descriptions, approximate methodologies are employed, including density functional theory. Characterization of inorganic compounds: Because of the diverse range of elements and the correspondingly diverse properties of the resulting derivatives, inorganic chemistry is closely associated with many methods of analysis. Older methods tended to examine bulk properties such as the electrical conductivity of solutions, melting points, solubility, and acidity. Now several techniques were used for this subject such as: X-ray crystallography, Various forms of spectroscopy like ;  Ultraviolet-visible spectroscopy: NMR spectroscopy: Infrared spectroscopy: Electron nuclear double resonance , Mössbauer spectroscopy 3 Structure of Atom First off all we will investigate some fundamental aspects of molecules and chemical reactions: - Why do only certain combinations of atoms form stable molecules? - What are the molecular structures of molecules? - How are the characteristics of molecules related to the macroscopic properties, such as chemical reactivity and physical properties ? To answer these questions - we clearly need to get a better picture of what atoms are and how they are bound together both within a molecule (i.e., what is a “chemical bond”?) and among molecules (what holds the molecules in liquids and solids together?). Particles and Waves: By the late 19th century, physicists thought they had most physical phenomena pretty well understood. All things pretty much fell into two distinct categories: waves and particles.“Particles” were defined by the way they interacted with each other, and similarly for waves. So a “particle” is something that exhibits “particle-like behavior”. First, we’ll discuss a bit about particles, and particularly electrostatic forces between them. Then we’ll talk about early experiments to determine the properties of atoms. Then, we’ll return to a discussion of wave-like behavior, and show how the only way to describe it. Electromagnetic radiation: Electromagnetic radiation (“light”) is a form of energy, characterized by wavelength ( λ) and frequency ( ν) Wavelength (λ): The distance between two consecutive peaks in the wave. Frequency (ν): The number of waves (or cycles) that pass a given point in space per second. The product of wavelength ( λ) and frequency(ν) is a constant. Blackbody radiation: Heated bodies radiate energy, but what is the mechanism? On an atomic scale, heat causes the molecules and atoms of a solid to vibrate. As atoms consist of electrical charges in the form of electrons and protons, it is the vibration of these charges which is responsible for the emission of electromagnetic radiation. A very hot object will emit visible light as the electrons vibrate.How do bodies absorb radiation? In order to radiate energy, an object must first absorb it. Suppose we shine a light on an object. If we shine it on glass Light passes through. If we shine it on a metal Light is reflected. If we shine it on carbon Light is absorbed. 4 In glass the electrons are tightly bound to atoms and only oscillate at certain frequencies outside the range of visible light. This makes glass appear transparent as very little of the visible light is absorbed. • Blackbody radiators include: – Lava; – A hot stove top; – The sun; – You Blackbody radiation II: Metals conduct and have free electrons not bound to any particular atom. These electrons oscillate in response to the light and then radiate light themselves. This radiation is reflected light. Again, there is very little absorption of light, most of it is reflected. The electrons in carbon have a short mean free path, when they collide their energy is transferred to the lattice. They are efficient absorbers of the incident light, hence carbon appears black. Carbon and similar materials are effective at converting incident light into heat. In a reverse process, as the carbon atoms warm up and vibrate more vigorously, more of the lattice energy is transferred to the free electrons, thus carbon is also a good radiator of heat. It cools down much faster than a metal as it is more efficient at converting the lattice energy into radiation. Consider a box with all walls at a given temperature •Outside: - The spectrum of electromagnetic radiation given off by the outside is dependent on the material that the box is made of… •Inside: - It is a result of thermodynamics (empirically tested) that the spectrum of radiation inside the box is independent of the material of the walls • This spectrum is know as blackbody spectrum. • It would be characteristic of an object which was a perfect absorber, and so a perfect emitter as well… —A good example is a hole in a box! What statement is true when comparing red light to blue light? A. Red light travels at a greater speed than blue light. B. Blue light travels at greater speed than red light. C. The wavelength of blue light is longer. D. The wavelength of red light is longer. - this energy is proportional to the frequency of the wave, but is independent of the amplitude (intensity); the proportionality factor is a constant called Planck's constant (symbol h) E = hƲ - where h = 6.6 × 10-34 J/s 5 Origins of the spectrum: The energy spectrum is formed by a continuous process of absorption and re- emission of radiation by the atoms and molecules forming the walls of the box. In this way the energy can shift from one mode to another. When thermal equilibrium is reached the characteristic spectrum will be established. There are many examples besides the photoelectric effect in which light is either absorbed or emitted by atoms or molecules. In analogy with the photoelectric effect, a gas-phase atom (rather than one on the surface of a metal) can absorb light; if the frequency of the light is high enough, an electron can be emitted. Or, if the frequency is too low, it may be able to absorb the light, allowing one electron in the atom to rise to a higher energy. Or, for molecules, the energy absorbed from light could go toward rotating the molecule faster, or making vibrating bonds vibrate with greater amplitude, etc. If it is high enough in frequency, the light can be absorbed and the energy used to break a covalent bond, such as in the Cl molecule in the chain reaction demo. In all these cases, the energy of the photon is equal to 2 the change in the energy of the molecule or atom. If we say that the atom or molecule has initial energy Ei and final energy Ef > Ei then ε = E – E is just a statement of the conservation of energy. f i Types of spectra: Spectra are broadly classified into two groups (i) emission spectra and (ii) absorption spectra; i. Emission spectra are of three kinds (a) continuous spectra,(b) band spectra and (c) line spectra. Continuous spectra: Solids like iron or carbon emit continuous spectra when they are heated until they glow. Continuous spectrum is due to the thermal excitation of the molecules of the substance. Band spectra: The band spectrum consists of a number of bands of different colors separated by dark regions. The bands are sharply defined at one edge called the head of the band and shade off gradually at the other edge. Band spectrum is emitted by substances in the molecular state when the thermal excitement of the substance is not quite sufficient to break the molecules into continuous atoms. Line spectra: A line spectrum consists of bright lines in different regions of the visible spectrum against a dark background. All the lines do not have the same intensity. The number of lines, their nature and arrangement depends on the nature of the substance excited. Line spectra are emitted by vapours of elements. No two elements do ever produce similar line spectra. ii. Absorption spectra: When a substance is placed between a light source and a spectrometer, the substance absorbs certain part of the spectrum. This spectrum is called the absorption spectrum of the substance. 6 Photoelectric Effect • As blue light strikes the metal foil, the foil emits electrons. • When red light hits the metal foil, the foil does not emit electrons. • Blue light has more energy than red light. • How could we get more energy into the red light? Try increasing the brightness. • Well, that didn’t work! Maybe its still not bright enough. Still not working. What happens with brighter blue light? More blue light means more electrons emitted, but that doesn’t work with red. Wave theory cannot explain these phenomena, as the energy depends on the intensity (brightness). According to wave theory bright red light should work! BUT IT DOESN’T! EINSTEIN in 1905 (he got the Nobel Prize for this): This can be understood if one assumes that light is quantized in the following sense: when light interacts with matter, it can give up or accept energy only in discrete packets or “quanta” ( Later named them “photons”); the energy of the created or destroyed photon being proportional to the light frequency, with Planck’s constant as the constant of proportionality: ε = hν = hc/λ Each atom in the metal can absorb at most one photon at a time. From this perspective, changing the intensity of the light just alters the number of photons that impinge on an area of the metal surface per second, and thus on the number of surface atoms at any moment that are in the vicinity of a photon that they can absorb. But the energy of each photon is determined only by the light frequency. Metal Foil Each metal has a minimum energy needed for an electron to be emitted. This is known as the work 9 function, W. So, for an electron to be emitted, the energy of the photon, hƲ, must be greater than the work function, W. The excess energy is the kinetic energy, E of the emitted electron. EINSTEIN’S PHOTOELECTRIC EQUATION:- E= hƲ - W 7 Applications: The Photoelectric effect has numerous applications, for example night vision devices take advantage of the effect. Photons entering the device strike a plate which causes electrons to be emitted, these pass through a disk consisting of millions of channels, the current through these are amplified and directed towards a fluorescent screen which glows when electrons hit it. Image converters, image intensifiers, television camera tubes, and image storage tubes also take advantage of the point-by-point emission of the photocathode. In these devices an optical image incident on a semitransparent photocathode is used to transform the light image into an “electron image.” The electrons released by each element of the photo emitter are focused by an electron-optical device onto a fluorescent screen, reconverting it in the process again into an optical image. Solar panels are nothing more than a series of metallic plates that face the Sun and exploit the photoelectric effect. The light from the Sun will liberate electrons, which can be used to heat your home, run your lights, or, in sufficient enough quantities, power everything in your home. Kinetic energy of emitted electron vs. Light frequency: Higher-frequency photons have more energy, so they should make the electrons come flying out faster; thus, switching to light with the same intensity but a higher frequency should increase the maximum kinetic energy of the emitted electrons. If you leave the frequency the same but crank up the intensity, more electrons should come out (because there are more photons to hit them), but they won't come out any faster, because each individual photon still has the same energy. And if the frequency is low enough, then none of the photons will have enough energy to knock an electron out of an atom. So if you use really low-frequency light, you shouldn't get any electrons, no matter how high the intensity is. Whereas if you use a high frequency, you should still knock out some electrons even if the intensity is very low. Photoelectricity Experimental Summary: 1) A metal shows a PE only if the incident light has a frequency above a certain threshold frequency . 2) If light of a given frequency does produce a PE, the photoelectric current from the surface is proportional to the intensity of the light falling on it 3) If light of a given frequency releases photoelectrons, the emission of these electrons is immediate 4) The KE of the emitted electrons display a maximum value, which is proportional to the frequency of the incident light (above the threshold frequency) 5) The maximum KE of the photoelectrons increases in direct proportion to the frequency of the light that causes their emission. The max. KE is not dependant on the intensity of the incident light, as the classical wave theory of light would require. 8 - the question that stumped physicists was: How could a low- intensity train of light waves spread out over a large number of atoms, concentrate, in a very short time interval, enough energy on one electron to knock the electron out of the metal? - according to classical wave theory, there was no reason why a high intensity beam of low frequency light should not produce photoelectricity if a low intensity beam of light at high frequency did - secondly, classical wave theory could not explain why higher frequency light ejected photoelectrons with more KE but the intensity light had no effect on KE First major classification of matter is the division of physical and chemical properties. physical properties of a substance are those properties that do not depend on a chemical change in the substance in order to be defined. Some examples of physical properties are listed below. • Mass; Volume; Color; Freezing Point; Boiling Point; Viscosity The chemical properties of a substance are those properties that depend on a chemical change or reaction to occur in order to be defined. Some examples of chemical properties are listed below. • Corrosion Rate; Heat of Combustion; Enthalpy of Formation; Toxicity; Reactivity with Solvents When asked to identify a property of a substance as either physical or chemical simply decide whether a reaction or change is necessary in order to measure the property. If reaction or change is necessary, the property is chemical in nature. If no reaction or change is necessary, the property is physical in nature. Atomic Structure: How would you “define” an atom? Probably by talking about composition and internal structure extremely tightly localized nucleus comprised of protons (positively charged) neutrons (electrically neutral, almost identical mass) electrons (negatively charged, much lower mass) far outside the nucleus ... or something like that. You might talk about electrostatic attractions between the positively charged nucleus and negatively charged electrons that hold it together. In short - you would discuss the atoms as particles, consisting of subatomic particles. That’s what people tried to do at the beginning of the 20th century. We will describe how it was discovered that treating atomic constituents as exhibiting solely “particle-like behavior” inevitably lead to problems: inconsistencies and incorrect predictions. In fact, in order to begin to understand the glue that holds together a covalent bond, we will need to revise our picture completely. 9 Background Information: 1. Element – atoms with the same number of protons are of the same element 2. Isotope – atoms of the same element with different numbers of neutrons are different isotopes of that element 3. Atomic Number = Number of Protons 4. Number of Protons = Number of Electrons 5. Atomic Mass = Number of Protons + Number of Neutrons. Atomic Structure Fundementas: Atomic structure is fundamental to inorganic chemistry, perhaps more so even than organic chemistry because of the variety of elements and their electron configurations that must be dealt with. This material is essential to the understanding of organic molecular structure and, later on, reaction mechanisms. Most of this material is a review of general chemistry. You might find it helpful to keep a general chemistry textbook available for reference purposes throughout the organic chemistry course. The following diagram summarizes the basic facts of the structure of the atom. 10