CHEM 171 Lecture Notes - Lecture 1: Ionic Compound, Beryllium, Chemical Bond

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Published on 25 Dec 2015
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1. Chemistry Hour Exam I
When a chemical bond forms, the total energy of the compound is less than
that of the two separate atoms.
Ionic Bonds
Ionic solid – an assembly of cations and anions staked together in a
regular array
oExample of crystalline solids
Three main exceptions to octet formation
oHydrogen loses its only electron to form a bare proton
oLithium and Beryllium lose their 2s electrons, leaving a helium-like
duplet
When atoms in Periods 2 and 3 lose their valance electrons, they form
ions with the electron configuration of the preceding Nobel Gas
Elements in Period 4 lose their –s and –p electrons, they leave a noble-
gas core surrounded by an additional, complete subshell of d-electrons.
oThe d- orbitals lie below the s- orbitals, meaning the s- orbitals are
lost first
oMany metallic elements in the p- and d- blocks can lose a variable
number of electrons
This is called variable valance
Non-metallic elements rarely lose electrons in chemical reactions
oThey fill their electron shells to the configuration of the next noble
gas.
Lewis Symbols
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The Lewis symbol is a visual summary of the valance-shell electron
configuration
To work out the formula of an ionic compound by using Lewis symbols:
oRepresent the cation by removing the appropriate number of dots
from the symbol for the metal atom.
oRepresent the anion by transferring those dots to the Lewis symbol
for the nonmetal atom to complete its valance shell.
oIf necessary, adjust the numbers of the atoms of each kind so that
all the dots removed from the metal atom symbols are
accommodated by the nonmetal atom symbols.
oWrite the charge of each ion as a superscript in the normal way
The Energetics of Ionic Bond Formation
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