Post on 21-Feb-2016
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Valence Electrons The electrons responsible for the
chemical properties of atoms are those in the outer energy level.
Valence electrons - The electrons in the outer energy level or shell–the highest occupied energy level
Inner electrons -those in the energy levels below.
Keeping Track of Electrons Atoms in the same column...
–Have the same outer electron configuration.
–Have the same valence electrons. Easily found: same as the main group
number on the periodic table. Group 2: Be, Mg, Ca, Sr, Ba.
–2 valence electrons
Electron Dot diagrams A way of keeping track of
valence electrons. How to write them? Write the symbol. Put one dot for each
valence electron Don’t pair up until they
have to.
X
The Electron Dot diagram for Nitrogen
Nitrogen has 5 valence electrons.
First we write the symbol. NThen add 1 electron at a time to each side.Until they are forced to pair up.
Electron Configurations for Cations
Metals lose electrons to attain noble gas configuration (full outer shell).
They make positive ions (cations) If we look at the electron configuration,
it makes sense to lose electrons: Na 2,8,1 1 valence electron Na+ 2,8 noble gas configuration
Electron Dots For Cations Metals will have few valence
electrons (usually 3 or less)
Ca
Electron Dots For Cations Metals will have few valence electrons These will come off
Ca
Electron Dots For Cations Metals will have few valence electrons These will come off Forming positive ions
Ca2+noble gas configuration
Electron Configurations for Anions
Nonmetals gain electrons to attain noble gas configuration.
They make negative ions (anions) Halide ions- ions from chlorine or other
halogens that gain electrons S (2,8,6) - 6 valence electrons S2- (2,8,8) - a noble gas configuration.
Electron Dots For Anions Nonmetals will have many valence
electrons (usually 5 or more) They will gain electrons to fill outer shell.
P P3-
Stable Electron Configurations All atoms react to achieve noble gas
configuration. Noble gases have 8 outer shell
(valence) electrons. This is also called the octet rule.
Ar
Ionic BondingBetween metals and non-metalsTransfer of electronsFull outer shellsOppositely charged ions createdIons held to one another by
electrostatic attractionGiant structure formed
Ionic BondsCharacteristics of ionic compounds Usually soluble in water Electrical conductors when molten
and when in aqueous solution. High m.p. Brittle, hard crystals
Ionic Bonding Anions and cations are held
together by opposite charges. Ionic compounds are called salts. Simplest ratio is called the formula
unit. The bond is formed through the
transfer of electrons. Electrons are transferred to achieve
noble gas configuration.
Ionic Bonding
Na Cl
Ionic Bonding
Na+ Cl-
Ionic Bonding All the electrons must be accounted for
Ca P
Ionic Bonding
Ca P
Ionic Bonding
Ca2+ P
Ionic Bonding
Ca2+ PCa
Ionic Bonding
Ca2+ P 3-
Ca
Ionic Bonding
Ca2+ P 3-
Ca P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+ P
Ca
Ionic Bonding
Ca2+ P 3-
Ca2+ P 3-
Ca2+
Ionic Bonding
= Ca3P2 Formula Unit
Calcium Phosphide
Classwork problems (a)Show the bonding between the following1. Magnesium and Oxygen2. Potassium and Chlorine3. Calcium and Fluorine4. Lithium and Nitrogen5. Aluminium and Fluorine
Properties of Ionic Compounds Crystalline structure, usually solids A regular repeating arrangement of
ions in the solid Ions are strongly bonded together. Structure is rigid. High melting points Electrical conductors when melted Electrical conductors in solution
Crystalline structure
Conducting electricity Conducting electricity is allowing charges to
move. In a solid, the ions have charges but are locked
in place. Ionic solids are insulators. When melted, the charged ions can move
around. Melted ionic compounds conduct electricity.– To melt NaCl, it must get to about 800 ºC.
Dissolved in water (aqueous) the ions are now free to move and they conduct electricity.
Ionic solids are brittle
+ - + -+- +-
+ - + -+- +-
Ionic solids are brittle
+ - + -
+- +-+ - + -
+- +-
Displacing the top layer (diagram) puts ions of the same charge near one another creating strong repulsion that breaks the crystal apart.
Solubility Ionic solids are often (but not always)
soluble in water. Solubility usually (but not always)
increases with increasing temperature.