Valence Electrons:

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Valence Electrons
ELECTRONS AVAILABLE FOR BONDING
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CA Standards

• Students know how to use the periodic table to
  determine the number of electrons available for
  bonding.
• Students know how to draw Lewis dot structures.

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Definition

• Valence electrons
• electrons in the outmost shell (energy level).
  They are the electrons available for bonding.

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Group 1 (alkali metals) have 1 valence electron
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Group 2 (alkaline earth metals) have 2 valence
electrons
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Group 13 elements have 3 valence electrons
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Group 14 elements have 4 valence electrons
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Group 15 elements have 5 valence electrons
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Group 16 elements have 6 valence electrons
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Group 17 (halogens) have 7 valence electrons
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Group 18 (Noble gases) have 8 valence electrons,
except helium, which has only 2
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Transition metals (d block) have 1 or 2 valence
electrons
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Lanthanides and actinides (f block) have 1 or
2 valence electrons
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Reactivity

• of valence electrons determine reactivity
• Alkali Metals Most reactive metal
• 1 v.e , loosing one allows full octet
• Halogen Most reactive nonmetal
• 7 v.e, gaining one allows full octet
• Noble Gas not reactive
• 8 v.e, complete octet

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Ionic Bonding
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CA Standards

• Students know atoms combine to form molecules by
  sharing electrons to form covalent or metallic
  bonds or by exchanging electrons to form ionic
  bonds.
• Students know salt crystals, such as NaCl, are
  repeating patterns of positive and negative ions
  held together by electrostatic attraction.

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Bonds

• Forces that hold groups of atoms
• together and make them function
• as a unit.

• Ionic bonds transfer of electrons
• Covalent bonds sharing of electrons

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The Octet Rule Ionic Compounds
Ionic compounds form so that each atom, by
gaining or losing electrons, has an octet of
electrons in its highest occupied energy
level. Metals lose electrons to form
positively-charged cations Nonmetals gains
electrons to form negatively-charged anions
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Ionic BondingThe Formation of Sodium Chloride

• Sodium has 1 valence electron

• Chlorine has 7 valence electrons

• An electron transferred gives
• each an octet

Na 1s22s22p63s1
Cl 1s22s22p63s23p5
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Ionic BondingThe Formation of Sodium Chloride
This transfer forms ions, each with an octet
Na 1s22s22p6
Cl- 1s22s22p63s23p6
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Ionic BondingThe Formation of Sodium Chloride
The resulting ions come together due to
electrostatic attraction
(opposites attract)
Cl-
Na
CATION
ANION
The net charge on the compound must equal zero
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Examples of Ionic compounds
Mg2Cl-2
Magnesium chloride Magnesium loses two electrons
and each chlorine gains one electron
Na2O2-
Sodium oxide Each sodium loses one electron and
the oxygen gains two electrons
Aluminum sulfide Each aluminum loses two
electrons (six total) and each sulfur gains two
electrons (six total)
Al32S2-3
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Metal Monatomic Cations Ion name
Lithium Li Lithium
Sodium Na Sodium
Potassium K Potassium
Magnesium Mg2 Magnesium
Calcium Ca2 Calcium
Barium Ba2 Barium
Aluminum Al3 Aluminum
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Nonmetal Monatomic Anions Ion Name
Fluorine F- Fluoride
Chlorine Cl- Chloride
Bromine Br- Bromide
Iodine I- Iodide
Oxygen O2- Oxide
Sulfur S2- Sulfide
Nitrogen N3- Nitride
Phosphorus P3- Phosphide
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Sodium Chloride Crystal Lattice
Ionic compounds form solid crystals at ordinary
temperatures.
Ionic compounds organize in a characteristic
crystal lattice of alternating positive and
negative ions.
All salts are ionic compounds and form crystals.
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Properties of Ionic Compounds
Structure Crystalline solids
Melting point Generally high
Boiling Point Generally high
Electrical Conductivity Excellent conductors, molten and aqueous
Solubility in water Generally soluble
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Ionic Compound Formulas
www.lab-initio.com
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Ions

• Cation A positive ion
• Mg2, NH4
• Anion A negative ion
• Cl-, SO42-

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Predicting Ionic Charges
Group 1
Lose 1 electron to form 1 ions
H
Li
Na
K
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Predicting Ionic Charges
Group 2
Loses 2 electrons to form 2 ions
Be2
Mg2
Ca2
Ba2
Sr2
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Predicting Ionic Charges
Group 13
Loses 3 electrons to form 3 ions
B3
Al3
Ga3
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Predicting Ionic Charges
Group 14
Lose 4 electrons or gain 4
electrons?
Neither! Group 14 elements rarely form ions.
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Predicting Ionic Charges
Nitride
N3-
Group 15
Gains 3 electrons to form 3- ions
Phosphide
P3-
As3-
Arsenide
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Predicting Ionic Charges
Oxide
O2-
Group 16
Gains 2 electrons to form 2- ions
S2-
Sulfide
Se2-
Selenide
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Predicting Ionic Charges
Group 17
Gains 1 electron to form 1- ions
F1-
Fluoride
Cl1-
Chloride
Br1-
Bromide
I1-
Iodide
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Predicting Ionic Charges
Group 18
Stable Noble gases do not form ions!
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Predicting Ionic Charges
Groups 3 - 12
Many transition elements
have more than one possible oxidation state.
Iron(II) Fe2
Iron(III) Fe3
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Predicting Ionic Charges
Groups 3 - 12
Some transition elements
have only one possible oxidation state.
Zinc Zn2
Silver Ag
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Writing Ionic Compound Formulas
Example Aluminum sulfide
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Al3
S2-
Al2
S3
2
3
Not balanced!
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• Shortcut to determining formula (Criss-Cross
  method)
• 1. ________ from charge becomes the subscript.
• 2. All ionic compounds are _________ (no or
  -).
• 3. Subscripts are written in ________ possible
  ratio.
• The number 1 is never written (It is implied).
• Examples

Number
neutral
lowest
Ex. Al3 O2-
Ex. Li O2-
Al2O3
Li2O
(Aluminum oxide)
(Lithium oxide)
Ex. Ca2 O2-
Ex. Mg2 N3-
Mg3N2
Ca2O2
CaO
(Calcium oxide)
(Magnesium nitride)
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Learning Check

• Write the correct formula for the compounds
  containing the following ions
• 1. Na, S2-
• a) NaS b) Na2S c) NaS2
• 2. Al3, Cl-
• a) AlCl3 b) AlCl c) Al3Cl
• 3. Mg2, N3-
• a) MgN b) Mg2N3 c) Mg3N2

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Solution

• 1. Na, S2-
• b) Na2S
• 2. Al3, Cl-
• a) AlCl3
• 3. Mg2, N3-
• c) Mg3N2

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Writing Ionic Compound Formulas
Example Magnesium carbonate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
Mg2
CO32-
Mg
CO3
They are balanced!
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Writing Ionic Compound Formulas
Example Zinc hydroxide
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
( )
Zn2
OH-
(OH)2
Zn
2
Not balanced!
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Writing Ionic Compound Formulas
Example Aluminum phosphate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
Al3
PO43-
Al
PO4
They ARE balanced!
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Writing Ionic Compound Formulas
Example Barium nitrate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Ba2
NO3-
( )
Ba
(NO3)2
2
Not balanced!
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Writing Ionic Compound Formulas
Example Ammonium sulfate
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
NH4
( )
SO42-
2
(NH4)2
SO4
Not balanced!
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Writing Ionic Compound Formulas
Example Iron(III) chloride
1. Write the formulas for the cation and anion,
including CHARGES!
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need more than
one of a polyatomic ion.
Fe3
Cl-
Fe
Cl3
3
Not balanced!
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Naming Compounds
Binary Ionic Compounds

• 1. Cation first, then anion
• 2. Monatomic cation name of the element
• Ca2 calcium ion
• 3. Monatomic anion root -ide
• Cl- chloride
• CaCl2 calcium chloride

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Naming Ionic Compounds

• Cation first, then anion
• Monatomic cation name of the element
• Ca2 calcium ion
• Monatomic anion root -ide
• Cl- chloride
• CaCl2 calcium chloride

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• Formula to name
• a. Li2O _________________
• b. Al2O3 _________________
• c. CaO _________________
• d. Mg3N2 _________________

Lithium oxide
Aluminum oxide
Calcium oxide
Magnesium nitride
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Naming Binary Ionic Compounds

• Examples
• NaCl
• ZnI2
• Al2O3

sodium chloride zinc iodide aluminum oxide
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Learning Check

• Complete the names of the following binary
  compounds
• Na3N sodium ________________
• KBr potassium ________________
• Al2O3 aluminum ________________
• MgS _________________________

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Naming Ionic Compounds(continued)
Metals with multiple oxidation states

• some metal forms more than one cation
• use Roman numeral in name
• PbCl2
• Pb2 is cation
• PbCl2 lead(II) chloride

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Examples
Ions Formula Name





Iron (II) hydroxide
Fe2 OH-
Fe(OH)2
Ferrous hydroxide
Ca2 CN-
Ca(CN)2
Calcium cyanide
NH4 O2-
(NH4)2O
Ammonium oxide
NaCN (No Parentheses b/c only 1)
Sodium cyanide
Na CN-
Cobalt (III) hydroxide
Co(OH)3
Co3 OH-
Cobaltic hydroxide