CHMA10H3 Lecture 28: CHMA10 Lecture 25

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CHMA10 Lecture 25: Lewis Structures and Ionic Bonding Model
- Lewis Structures: an introduction to covalent bonding
o Bonding Pair electrons: shared pair of electrons associated with the bond
o Lone Pair electrons : electrons not involved in bonding
o Method for drawing Lewis structures
1: determine total number of valence electrons of the element or
elements involved in a bond
2: draw all of the elements involved and connect them
The central atom is usually the one with the lower group number
out of all of them
o Will the most leftward element on the period table
3: Subtract bonding electrons from the valence electron total
Distribute the remaining electrons among the non-central atoms
as lone pairs
4: if any non-hydrogen atoms lack an octet, form double or triple bonds
Tends to be seen in less electronegative atoms
- Ionic Bonding Model
o Lattice Energy: energy associated with forming a crystalline lattice of attending
cations/anions from gaseous ions
when forming ionic salts, you have electrostatically attracted cations and
anions
this attractions the potential energy of the involved elements
potential energy is lower than if the elements were to be
unbound
energy difference between individual ions and crystal is released
as lattice energy
o Born-Haber cycle: represents formation of ionic compound from its elements
4 main steps needed to get to the electrostatic attraction involved in the
Born-Haber cycle
1: Need to sublime solid to gas
o Endothermic process requiring energy
o End with a solid metal being converted to a gaseous form
2: Need to ionize an electron out of the metal which is in the gas
phase
o Can determine how much energy is needed to ionize an
electron out by looking at the ionization energy of the
elements involved
o Process is endothermic as well
3: Need to have the non-metal component of the ionic compound
present in the correct ratio
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