This chapter looks at the molecular orbital theory (MO theory) of heteronuclear diatomic
molecules and ions, which introduces the possibility that atomic orbitals on two atoms
contribute unequally to the molecular orbital. It points out how polarity can be expressed
in terms of the concept of electronegativity. It also examines the bonding molecular orbital
of a heteronuclear diatomic molecule or ion which is composed mostly of the atomic orbital
of the more electronegative atom. The chapter describes the electron distribution in the
covalent bond between the atoms in a heteronuclear species, which is considered not
symmetrical between the atoms as it is energetically favourable for a bonding electron pair
to be found closer to one atom rather than the other. It mentions the polar bond, which is a
covalent bond in which the electron pair is shared unequally by two atoms.
Chapter
Molecular orbital theory: heteronuclear diatomics
Chapter
The Carbonyl Group and its Chemistry
Matthew Ingram
This chapter discusses the nature of the carbonyl group and the chemistry it can undergo. The chemistry of the carbonyl group can be found in lots of situations: in the body, in the environment, in manufacturing, and in pharmaceutical applications. At the heart of the chemistry of the carbonyl group is the carbonyl bond, a double bond comprising one σ and one π bond, which joins carbon and oxygen. The chapter points out the difference in electronegativity between carbon and oxygen, citing a dipole moment that exists between the two atoms. The carbonyl group is central to pharmaceutical chemistry and is present in many drug molecules and is present in many different types of compound.
Chapter
Acids and bases
This chapter discusses equilibria and factors effecting acidity and basicity of organic compounds and other areas of chemistry, such as electronegativity of the atom that bear the charge. It examines delocalization, resonance, inductive effects, indicators, and interactions between molecules and ions. It also deals with the protonation on the carbonyl oxygen atom that gives the more stable, delocalized protonated form of the COOH group. The chapter mentions the inductive electron-withdrawing effect of the C=O that helps to weaken the adjacent O-H bond and carboxylic acids that are more acidic than alcohols, whose anions are not stabilized by delocalisation. It refers to Tenormin, which is a drug used in the treatment of high blood pressure, angina, and abnormal heart rhythms.
Chapter
Zintl isoelectronic relationships
This chapter examines Zintl isoelectronic relationships. The chapter starts by noting how many binary compounds are formed between the Group 1 and 2 elements and Groups 13–15. The Zintl concept utilizes isoelectronic relationships in order to provide some insight into the solid state structures adopted by such compounds. The chapter highlights that the electronegativity differences between the atoms are sufficiently large in these compounds that, to a first approximation, an ionic formulation is reasonable. The isoelectronic relationship is then used as a basis for rationalizing the manner in which the Group 13–15 elements aggregate in the solid state. Next, the chapter explains that many of the anionic species observed in Zintl phases in the solid state are not observed as stable solution species. This is because their large negative charges make them very nucleophilic and therefore sensitive to the slightest traces of moisture.
Chapter
The Halogens
This chapter discusses the halogens, also known as either Group 17 or Group VII. It also notes the exception of featuring astatine due to its high radioactivity. The physical properties of the halogens range between the melting points, boiling points, atomic radius, ionic radius, electronegativity, ionization energy, and dispersion forces. Additionally, the oxidizing ability of the halogens decreases in positivity, while the reducing ability of the halide ions increases. Fluorine is known to be exceptionally strongly oxidizing. Aqueous halide ions are tested by adding aqueous silver nitrate acidified with dilute nitric acid. An equilibrium is set up when chlorine dissolves in water.
Chapter
Transition Metals 1
This chapter discusses the halogens, also known as either Group 17 or Group VII. It also notes the exception of featuring astatine due to its high radioactivity. The physical properties of the halogens range between the melting points, boiling points, atomic radius, ionic radius, electronegativity, ionization energy, and dispersion forces. Additionally, the oxidizing ability of the halogens decreases in positivity, while the reducing ability of the halide ions increases. Fluorine is known to be exceptionally strongly oxidizing. Aqueous halide ions are tested by adding aqueous silver nitrate acidified with dilute nitric acid. An equilibrium is set up when chlorine dissolves in water.
Chapter
Bonding and Molecular Shape
This chapter discusses bonding and molecular shape of electrons. A covalent bond occurs when atoms share a pair of similar electrons. Modern theories on covalent bonding are dominated by molecular orbital theory. Polar covalent bonds occur when different atoms share the electron pair unequally due to electronegativity. With benzene being the most familiar molecule of the bonding, delocalization happens when more than two atoms are involved in the bonding. The valence-shell electron-pair repulsion (VSEPR) theory can help us to visualize the shapes of simple molecules. Additionally, ionic bonding occurs when an atom transfers an electron to another atom and the ions formed a crystal lattice electrostatically.
Chapter
Effective atomic number rule to exchange energy
This chapter assesses the effective atomic number rule. The effective atomic number rule applies to molecules where covalent bonding is strong and all the valence orbitals are being used in either homo- and hetero-polar covalent bonds or are occupied by non-binding electron-pairs. If the molecule is unable to achieve the octet or 18-electron configurations by virtue of donation from the ligands, then element–element bonds may be formed. The chapter then looks at electrode potential, before considering electron affinity and deficiency. The electron affinity is the negative of the electron capture enthalpy, while an electron deficient molecule has fewer valence electrons involved in covalent bonds than the number of orbitals available. The chapter also studies electronegativity, the electroneutrality principle, electropositivity, entropy, and exchange energy.
Chapter
Atomic structure
This chapter provides foundations for an explanation of the trends in the physical and chemical properties of all inorganic compounds. The chapter begins with a discussion on the origin of matter in the solar system and then considers the development of understanding of atomic structure and the behaviour of electrons in atoms. It reviews the structures and properties of atoms, acknowledging that these are crucial in understanding the behaviour of molecules and solids. The chapter also qualitatively introduces quantum theory and uses the results to rationalize properties such as atomic radii, ionization energy, electron affinity, and electronegativity.
Chapter
Factors influencing the chemical shift and coupling constants
This chapter surveys the chemical factors that influence the chemical shift and the magnitude of coupling constants. Shielding is influenced by the fields generated by circulation of ground state electrons around the nucleus (diamagnetic term) and by electrons mixed in from excited states (the paramagnetic term). The diamagnetic contribution is usually small and dominates for light elements, resulting in (usually) small chemical shift ranges for these elements. The paramagnetic term dominates for heavier elements and is often large, resulting in large chemical shift ranges for these elements. The chemical shift is influenced by many, often competing factors, including oxidation state, electronegativity, coordination number, and bonding to other atoms. Meanwhile, scalar coupling constants are influenced by similar factors and by geometric factors, particularly interbond and dihedral angles. If all other factors are kept constant, scalar couplings between different isotopes of the same elements scale with gyromagnetic ratio.
Chapter
Periodicity in the properties of s- and p-block atoms
This chapter discusses a range of properties of isolated atoms of the s- and p-block elements which will introduce the ideas of periodicity. It begins by looking at the idea of effective nuclear charge, which is useful in understanding many aspects of periodicity; but in order to utilize and appreciate the concept fully, a quantitative scale is desirable whereby we can look at values and trends in values for the valence electrons of the elements in which we are interested. The chapter then considers ionization energies and electron affinities. The ionization energy is the energy required to completely remove an electron from an atom in the gas phase, while the electron affinity of an atom is defined as the energy change which occurs when an electron is added to an atom (or ion). The chapter also studies covalent and ionic radii; electronegativity; orbital energies and promotion energies; and relativistic effects.
Chapter
Periodicity in the properties and structures of the elements
This chapter examines the properties of the elements themselves and provides an understanding of the origin of the observed periodic trends. The first, and perhaps most important, point to note is that the p-block is the only part of the periodic table which contains non-metals. Moreover, within the p-block, the metals are found in the bottom left-hand corner while the so-called metalloids or semi-metals lie along a diagonal from top left to bottom right with the non-metals occupying the top right. There is, therefore, a trend from metallic to non-metallic character as we move from bottom left to top right. This pattern correlates precisely with the trend seen for the element electronegativity discussed in the previous chapter. A final point of interest while dealing with the elements themselves concerns the so-called binding energies (or atomization energies), which relate to the magnitude of the interatomic forces which bind the elements together.
Chapter
Compounds of the s- and p-block elements
This chapter assesses s- and p-block element compounds and their properties. It begins by looking at halides, which is a large and diverse group of compounds, particularly in terms of the variety of structural types encountered. Halides include fluorides and chlorides. The chapter then considers ionic compounds, element oxides, and element hydrides. All the hydrides are molecular covalent species, but the trends in melting and boiling points are worthy of comment. In Group 14, one sees a progression to higher melting and boiling points as the group is descending resulting from the increasing van der Waals forces between the molecules. This is also largely the case for the Group 16 hydrides but with the obvious exception of H2O. The explanation for this feature is the extensive intermolecular hydrogen bonding between oxygen lone pairs and hydrogen, this being that much greater for the lighter element oxygen due to its high electronegativity.
Chapter
Atoms, Molecules, and Chemical Bonding—a Review
This chapter presents an overview of organic chemistry and looks at the compounds of carbon. It argues that there are hugely more compounds of carbon than of all other elements combined. The chapter then discusses the special properties of the element, and the characteristics of the carbon atom. It begins the study of organic chemistry by reviewing the nature of atoms and, in particular, their electronic structures. The chapter also looks at valence electrons and ionic and covalent bonds. It then explains the method of representing atoms which gave prominence to their valence electrons and facilitated comparisons between different elements. The chapter then demonstrates the periodic table by looking at the Lewis representations of atoms. Finally, the chapter analyzes several scales to quantify electronegativity. It also considers bond polarity and an introduction to resonance.
Chapter
Organometallic Compounds of Main Group Elements
This chapter discusses the main group of organometallic compounds which contain metal–carbon σ-bonds generated by orbital overlap along the M–C axis. It reviews the possibility of interaction of the metal with the π-electron systems of unsaturated organic compounds, in particular, when the unsaturated moiety carries a negative charge. The chapter also looks at one important aspect that governs the reactivity of organometallic species: the polarity of the Mδ+ Cδ-bond. It explicates the nature of bond polarity, then studies the concept of electronegativity and ‘group electronegativity’. Towards the end, the chapter turns to the reactivity of main group metal alkyls. It also considers ionic organometallics and lithium ions.
