Inorganic Quiz 2: Molecular Structure and Bonding

covalent bond

non-metals and metalloids only

sharing of electrons

metallic bond

pure metals and alloys

metal atoms lose electrons to a common “sea of electrons

the metal cations are cemented by the “electron sea”

ionic bond

metal with non-metal(s)

electrostatic attraction between ions

bond dissociation energy of H-H bond

436 kJ/mol

strong covalent bond

do H2 molecules attract each other?

only very weakly with dispersion forces

covalent bond directionality and localization

directional and localized

the bond has a specific orientation and the electrons sit in the region between the atoms.

bond dissociation energy of Li-Li bond

102 kJ/mol

a weak covalent bond

what state are Li2 molecules found at high T and room T?

high T: lithium vapor

room T: molecules stick together and lose 217 kJ/mol of energy and form 3D solid lithium metal

metallic bond directionality and localization

non-directional and delocalized

the bonds don’t point a certain way. electrons are part of an “electron sea".

what phase will Na atom and Cl atom bond to make NaCl?

gas phase

bond dissociation energy of Na-Cl bond

411 kJ/mol

directional and highly polar, 80% ionicity

what happens to NaCl molecules at room T?

they stick together, lose 230kJ/mol of energy and form a 3D crystal with 100% ionicity

ionic bond directionality

multidirectional

the cation is surrounded by anions and vice versa, so bonding can be in any direction you choose. no distinct molecules so we call them formula units.

diagram that predicts bonding based on electronegativity of the elements

Van Arkel - Ketalaar triangle

which of the bonding theory models work well together?

Lewis, VSEPR, and valence bond (VB) theory work well together

they are relatively simple and adequately describe the structure of most organic and many inorganic molecules

bonding theory that works well for molecular ionization and excited states

molecular orbitals (MO) theory

bonding theory that works well for s- and p-elements but not d- and f-

Lewis model

also not applicable to metallic bonding

how to calculate formal charge

count electrons in lone pairs and half the electrons it shares with other atoms. then, subtract that from the number of valence electrons.

formal charges vs oxidation numbers

oxidation numbers are determined by assuming full polarization and assigning all bonding electrons to the more EN atom (not sharing half like with formal charges)

structure of oxyacids and oxyanions

a central atom surrounded by OH groups and O atoms

no O-O (peroxy) fragments; they are weak

three exceptions to the octet rule

free radicals, electron deficient molecules (less than 8 Ve-), expanded octet (more that 8 Ve-)

unstable, short-lived molecules that tend to pair up to form stable molecules

free radicals

nitrogen monoxide exception (it is stable). MO theory needed to explain why.

element that commonly forms stable molecules with only 6 electrons in Lewis structures

boron (metalloid)

also hydrogen with only 2 electrons

why are expanded octets possible?

octet can be expanded for atoms in the 3rd period or below because:

1. they are large enough to accommodate more than eight electrons

2. 3d, 4d, or 5d orbitals may participate in bonding

bond enthalpy

same as bond energy

the amount of energy required to break a bond

shorter bonds are generally stronger (higher bond enthalpy)

polar bonds are stronger than non polar bonds

reaction enthalpy (delta Hrxn)

bond enthalpies of bonds broken - bond enthalpies of bonds formed

for gas phase reactions

only an approximation; better to use enthalpies of formation, experiments, or Hess’s law

how did Linus Pauling base his scale of ENs on?

on the difference between enthalpy of the polar bond compared to the average of the non polar bonds in the elements