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Advanced Chemistry

Advanced Chemistry. Chapter 8: Basic Concepts of Chemical Bonding Sections 8.1 – 8.5 Notes. What’s a Chemical Bond?. Whenever atoms or ions are strongly attached to one another, we say that there is a chemical bond Three types of Chemical Bonds Metallic Ionic Covalent.

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Advanced Chemistry

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  1. Advanced Chemistry Chapter 8: Basic Concepts of Chemical Bonding Sections 8.1 – 8.5 Notes

  2. What’s a Chemical Bond? • Whenever atoms or ions are strongly attached to one another, we say that there is a chemical bond • Three types of Chemical Bonds • Metallic • Ionic • Covalent

  3. Bond Types – Brief Review • Ionic • Refers to the electrostatic forces that exist between ions of opposite charge • Covalent • Results from the sharing of electrons between nonmetals • Metallic • Are relatively freely moving electrons found between metals

  4. Bond Polarity • Bond polarity is determine by differences in electronegativity Non-Polar Covalent 0.0 Polar Covalent 0.1- 1.9 Ionic Bond >2.0

  5. Dipole Moments • Covalent compounds with differences in electronegativity produce dipole moments, that’s why they are polar molecules! • Dipole moment increases with charge! u = Qr

  6. Calculating Dipole Moments u = Qr Where: u = dipole moment measured in debyes (D) Q = product of charges of atoms involved in bond r = separation of charge in meters (m) Convert using 1D = 3.34 x 10-30 C·m The distance between the centers (bond length) of H and Cl atoms in the HCl molecule is 1.27 Angstrom. A) Calculate the dipole moment using a +1 and -1 charge respectively

  7. Ionic Bonding • Attraction between ions..generally metals and nonmetals..this you know.. • But what happens to energy in ion formation? • Forming a cation (metals losing an electron) is an endothermic process..meaning energy is put in to remove an electron • Forming a anion (done by nonmetals) is an exothermic process • The difference between the processes is the overall energy change for one mole of reactant

  8. Ionic Bonds and Lattice Formation • The ions are drawn together and a lattice of ionic structure is formed • The Lattice Energy is the measure of how much stabilization results from the arranging of oppositely charged ions in an ionic solid • It is, the energy required to completely separate a mole of a solid ionic compound into its gaseous ions

  9. Lattice Energy Example NaCl(s) Na+(g) + Cl- (g) Hlattice = +788 kJ/mole This means the forming of NaCl is highly exothermic, H= -788 kJ/mole

  10. Lattice Energies • The large positive endothermic lattice energies makes ionic bonds strong.. • The strong attractions also make the compounds hard, brittle materials with high melting points Potential energy of two interacting charged particles relates by this equation Q1Q2 E = k r2

  11. Practice Problem • Which substance would you expect to have the greatest lattice energy? • AgCl, CuO, or CrN The greatest lattice energy results from the largest product of the ionic charges…thus CrN has (+3)(-3) = 9

  12. Electron Configuration of Ions • Ions like loose or gain electrons to form noble-gas electron formations • This results in the most energy-favorable and stable formation • Even though an increase in ionic states would result in a higher lattice energy, it is not enough to remove an electron from a completed energy level or add to an unfavorable higher energy level

  13. e- configuration of Transition Metals • Transition metals (d block) cannot reach the noble gas configuration due to their location on the table • So…they achieve stability by loosing electrons from the highest nshell.. • So, they loose valence electrons first, then as many d electrons as are required to reach the charge on the ion

  14. Example • Fe [Ar] 4s2 3d6 • In forming the Fe3+ ion, 2e- are lost from the 4s subshell and 1 from 3d so… • Fe3+ [Ar] 3d5

  15. Practice Problem • Write the electron configuration for Cr3+ [Ar] 3d3

  16. Sizes of ions • Ionic size plays a crucial role in determining the structure and stability of ionic solids • It determines both the lattice energy of the solid and the way in which the ions pack in a solid • Ionic size also determines the properties of ions in solutions

  17. Ion Size • Ion size depends on nuclear charge, the number of electrons it possesses, and the orbitals in which the outer electrons exist • Cations are smaller than their parent atoms • Anions are larger than their parent atoms • For Ions with the same charge, size increases as we go down a group in the PT

  18. Ion Size and isoelectronic series • The term isoelectronic means that the ions possess the same number of electrons • Ex: O2-, F-, Na+, Mg2+ and Al3+ • All have the configuration of Neon • The nuclear charge increases while # of e remain the same…so • Radius decreases due to larger attractive force between nucleus and electrons end

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