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Inorganic Lecture 9

Inorganic Lecture 9 - 1 Lecture 9 – Hydrogen • General...

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Unformatted text preview: 1 Lecture 9 – Hydrogen • General Information • Different types of hydrides • Hydrogen bonding • Preparation of H 2 • Industrial uses of H 2 • Hydrates and clathrates Hydrogen • The simplest atom – One proton and one electron • Of great importance in theoretical chemistry • 1 H NMR spectroscopy • We can talk about the element H in several ways – 1. As the diatomic gas H 2 – 2. As a proton (H + ) (or oxonium ion, H 3 O + ) – 3. As H-, the hydride ion 2 Some facts about Hydrogen • Most abundant element in the universe • 3rd most abundant on earth (after oxygen and silicon • Mainly in the form of water or hydrocarbons, plant material and animal material • H 2 is a colorless, odorless gas, sparingly soluble in all solvents at room temp and standard pressure • The single bond in H 2 is unusually strong for a single bond in a diatomic molecule Isotopes of Hydrogen • 3 isotopes of hydrogen, exhibit a greater difference in physical properties than the isotopes of any other element • Protium 1 H (or H) • Deuterium 2 H (or H) • Tritium 3 H (or H) – Found only in the upper atmosphere, radioactive – N + n → C + H • D-D > D-H > H-H (bond strength) 1 1 2 1 3 1 14 7 1 12 6 3 1 3 H(g) H + (g) + e- • The ionization energy of hydrogen is 1312 kJ/mol – Too high of a Δ H ion to exist under ordinary circumstances – [H 3 O] + is an important species in aqueous solution The Hydride Ion H(g) + e- H- (g) • Δ H EA = -73 kJ/mol • Alkali metal hydrides crystallize in the NaCl lattice • The radius of H- is estimated to be between 130-154 pm. Approximately the same size as that of F- (133 pm) • Cov radius H = 37 pm. Large increase in size for the H- ion attributed to electron- electron repulsion 4 Polar and Non-Polar E-H bond (where E = any element) • Hydrides are classified according to the polarity of the E-H bond • We determine the polarity or lack thereof by considering the electronegativity of H compared to the element in question • There are three possibilities – The hydrogen is more electronegative • The we can consider the H as H- or H δ- • The direction of the dipole is in the direction of the H – The hydrogen is less electronegative • Then we can consider the H as H + or H δ + • The direction of the dipole is in the direction of the other element – The hydrogen is about the same electronegativity • The bond is not polar • The bond is almost purely covalent (like C-H) Schematic of Polar E-H Bonds 5 HYDRIDES • A term usually used to mean “compounds that contain H” but it really means those which have “hydridic” character H- or H δ- – Saline hydrides • Polar bonds, Ionic • Hydrogen and an alkali metal • Hydrogen and an alkaline earth metal (except Be and Mg) – Transition metal hydrides • Different types of bonding depending on the metal, usually ionic with H δ-...
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Inorganic Lecture 9 - 1 Lecture 9 – Hydrogen • General...

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