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Chapter 3.3-3.4

CHEM 130 Chapter 3.3-3.4:Premium

6 pages65 viewsWinter 2019

Department
Chemistry
Course Code
CHEM 130
Professor
Charles Mc Mory
Chapter
3.3-3.4

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Saturday, February 9, 2019
3.3 Ions: Electron Configurations and Sizes
Every atom in a stable compound have a noble gas arrangement o electrons
Nonmetallic elements achieve a noble gas electron configuration by either sharing
electrons with nonmetals to form covalent bonds or by taking electrons from metals to
form ions
Nonmetals form anions and metals form cations
When two nonmetals react to form a covalent bond they share electrons in a way that
completes the valence electrons configuration of both atoms. Both nonmetals attain noble gas
electrons configurations
When a nonmetal and a representative-group metal react to form a binary ionic compound, the
ions form so that the valence electron configuration of the nonmetal achieves the electron
configuration of the next noble gas atom and the valence orbitals of the metal are emptied. In
this way both ions achieve noble gas electron configurations.
Predicting Formulas of Ionic Compounds
Ionic compound usually refer to the solid state of that compound.
in solid state ions are close together
contain large collection of positive and negative ions packed together in a way that
minimizes the -/- and +/+ reputation and maximizes the +/- attractions
In gas phase, pair of ions may get close enough to interact, but large collections of ions
do not exist
ex. O-s ion is not stable as an isolated gas phase species but is stable in many
solid ionic compounds
MgO(s), containing Mg2+ and 02- ions, is very stable, but isolated gas phase in pair
mg2+ anO2- is not energetically favorable in comparison with the separate neutral
gaseous atoms
Formation of an ionic compound from calcium and oxygen. We can predict what compound
will form by considering the valence electron configuration of the two
Electronegativity of oxygen is much greater than that of calcium
Because of large difference, electrons will be transferred rom calcium to oxygen to form
oxygen anions and calcium actions in the compound
How are electrons transferred?
Noble gas configurations are generally most stable
Oxygen needs 2 electrons to fill 2s and 2p valence orbital and to achieve the configurations
of neon (1s2 2s2 2p6)
By losing 2 electrons, calcium can achieve the configuration of argon. Two electrons are
transferred
To predict the formula of ionic compound, we recognize chemical compound are alway
electrically neutral (have same quantities of positive and negative charges)
Ca2+ and O2- ions are equal—> CaO
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Aluminum: [Ne]3s2 3p1 loses three electrons to form Al3+ ion and achieved neon
configuration
Al3+ and O2- form. But since it needs to be equal—> Al2O3
Common Ions with Noble Gas Configurations in Ionic Compounds
Exceptions
Tin forms Sn2+ and Sn4+ ions
Lead forms both Pb2+ and Pb4+ ions
Bismuth forms Bi3+ and Bi5+ ions
thallium forms Tl+ and Tl3+ ions
Sizes of Ions
Ion size plays role in determining structure and stability of ionic solids, the properties of
aqueous solutions, and the biologic effects of ions
Rely on atomic radii to measure distance for size (we don’t know exact size)- rely on trend
Ion size increases down a group
let to right is complicated because of the change from predominantly metal (left) to
nonmetals (right)
A given period contains both elements that give up electrons to form cations and Anions that
accept electrons to form ions
Sizes of ions related to positions of the elements on the periodic table.
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