BE 2800 Chapter 2 Objectives

Cite the distinctive electron configuration characteristic for each group of elements in the periodic table.

• Group 0- filled electron shells and stable electron configuration • Group VIIA and VIA- one or two electron deficient, respectively, from having stable structures • Groups IA and IIA- respectively having one and two electrons in excess of stable structures • Groups IIIB and IIB- have partially filled d electron states and in some cases one or two electrons in the next-higher energy shell • Groups IIIA, IVA, and VA- display characteristics that are intermediate between the metals and nonmetals by virtue of their valence electron structure

percent ionic character equation

%IC=(1-ⅇ^(-(0.25) (X_A-X_B )^2 ) )×100

Write the equation that relates energy and force.

E=Int(F*dr)

Ionic bonds

Electrically charged ions are formed by the transference of valence electrons from one atom type to another o Ceramics o Intermetallics

Covalent bonds

Sharing of electrons between adjacent atoms o Polymers o Ceramics o Semi-metals

Name the two atomic models cited, and note the differences between them.

The two atomic models are Bohr and wave mechanical. Whereas the Bohr model assumes electrons to be particles orbiting the nucleus in discrete paths, in wave mechanics we consider them to be wavelike and treat electron position in terms of a probability distribution.

Metallic bonding

Valence electrons are not bound to any particular atom in the solid and are more or less free to drift throughout the entire model o Metals o Semi-metals o Intermetallics

Hydrogen bonding

highly polar molecules form when hydrogen covalently bonds to a nonmetallic element

Van der Waal's bonding

relatively weak bonds resulting from attractive forces between electric dipole o Molecular solids

9. Using the general Gibbs Free Energy Equation for a reaction (G = H -TS), explain the behavior of water when a polar or charged solute, hydrophobic solute, or amphipathic solute is added to an aqueous system. Briefly explain why water expands when it freezes.

• Polar or charged solute- the solute is surrounded by the polar solvent forming complex, when the number of solvent molecules surrounding the charged solute is proportional to the coordination number of the charged solute o Decrease in entropy (but energy is released due to hydration) • Hydrophobic solute- it repels water so both solvation energy and lattice energy are positive o Enthalpy is highly positive, does not dissolve, non-spontaneous process • Amphipathic solute- has both hydrophobic and polar parts so depends on the relative ratio of both the parts

Describe the important quantum-mechanical principle that relates to electron energies.

• The energies of electrons are quantized- that is, only specific values of energy are allowed • The four electron quantum numbers are n, l, m(l) and m(s). They specify, respectively, electron orbital size, orbital shape, number of electron orbitals, and spin movement • According to Pauli exclusion principle, each electron state can accommodate no more than two electrons, which must have opposite spins.