Chapter 19: Chemical Bonding
“Isn’t It Ionic?”
Questions for Review
What atomic particle
determines the chemical
properties of an element?
a. protons b. neutrons c. electrons d. morons
What atomic particle
determines the chemical
properties of an element?
a. protons b. neutrons c. electrons d. morons
Which electrons determine an
element’s chemical properties?
a. electrons near the nucleus of the atom
b. middle energy level(s) c. valence electrons
Which electrons determine an
element’s chemical properties?
a. electrons near the nucleus of the atom
b. middle energy level(s)
c. valence electrons
How many valence electrons do most atoms need to become chemically stable?
a.1b.4c.8d.10
How many valence electrons do most atoms need to become chemically stable?
a.1b.4c.8d.10
Atoms are chemically stable (or resistant to change) when their valence shells are completely filled with electrons.
For most atoms, 8 electrons are needed to be chemically stable.
Why do the Noble Gases not form
compounds easily?
The valence shells of the Noble gases are already completely filled with electrons.
All of the Noble Gases, with the exception of helium, have 8 valence electrons. Helium has only two electrons.Therefore, the first energy level is full, making it stable with its two valence electrons.
How are electrons in an atom
represented?
a. Bohr Models b. Lewis Dot Diagrams c. both of these
How are electrons in an atom
represented?
a. Bohr Models b. Lewis Dot Diagrams c. both of these
Bohr Model of the Atom
Sodium atom Chlorine atom
How are valence electrons in an
atom represented?
a. Bohr Models b. Lewis Dot Diagrams c. both of these
How are valence electrons in an
atom represented?
a. Bohr Models b. Lewis Dot Diagrams c. both of these
See http://www.ausetute.com.au/lewisstr.html
Lewis Dot Diagrams
Why do chemical bonds
form?
Stability is achieved when the atoms…
have achieved a Noble Gas configuration (which have a complete set of valence electrons)
(In other words, atoms are stable when they have bonded with other atoms to completely fill their outer-level electron shells).
Chapter 19: Types of
Chemical Bonds1.Ionic Bonds = usually metal + nonmetal2. Covalent Bonds = nonmetal + nonmetal
What are ions?
How do ions form?
Ion
an atom that has gained or lost one or more electrons, therefore it has a positive or negative charge
Ionic BondUsually forms between a metal and a nonmetal
Is the force of electrostatic attraction between positively and negatively charged ions
Demonstration of Ionic Bonding
A transfer of electrons takes
place
If an atom loses electrons it becomes ____ charged.
If an atom gains electrons, it becomes ____ charged.
A transfer of electrons takes
place
If an atom loses electrons it becomes _positively_ charged.
If an atom gains electrons, it becomes _negatively_ charged.
Metals tend to lose electrons, becoming a positive ion (cation).
Nonmetals tend to gain electrons & become negative ions (anion).
Classify the following
compounds as covalent or ionic:
1.NaCl2.CO2
3.H2O
4.MgCl2
5.C4H10
Classify the following
compounds as covalent or ionic:
1.NaCl (ionic)2.CO2 (covalent)
3.H2O (covalent)
4.MgCl2 (ionic)
5.C4H10 (covalent)
Ionic Charges are indicated by a
Superscript
superscript -“written above”
Examples: Na+, Mg2+, Cl-, O2-
Chemical Formula Indicates the elements in a compound and the ratio of the atoms of those elements in one unit of the compound.
Chemical Formula• Examples: NaCl; H2O• The “2” in H2O is a subscript.
• Subscript (“written below”)indicates the number of atoms of an element in a unit of that compound.
• What is the ratio of sodium to chlorine in NaCl?
• What is the ratio of hydrogen to oxygen in H2O?
• What is the ratio of sodium to chlorine in NaCl? 1:1
• What is the ratio of hydrogen to oxygen in H2O? 2:1
Writing Formulas for Binary Ionic
Compounds Determine the oxidation number of
each ion (the number of electrons an atom gains or loses)
Oxidation numbers for the representative elements can be determined from its position on the periodic table. Oxidation Numbers for transition elements are determined from their negative ions.
Oxidation StateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound.
The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic.
Oxidation states are typically represented by integers, which can be positive, negative, or zero. http://en.wikipedia.org/wiki/Oxidation_state
Oxidation State In some cases the average oxidation state of an element is a fraction, such as 8/3 for iron in magnetite (Fe3O4).
The increase in oxidation state of an atom through a chemical reaction is known as an oxidation; a decrease in oxidation state is known as a reduction. Such reactions involve the formal transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation.
For pure elements, the oxidation state is zero.
http://en.wikipedia.org/wiki/Oxidation_state
Oxidation Numbers can be predicted from the
element’s position on the periodic table.
Writing Formulas for Binary Ionic
Compounds1. Write the symbol of the positive
ion first.2. Write the symbol of the negative
ion.3. Add the superscripts. Is the sum
zero?4. If the sum does NOT equal zero,
criss-cross the ionic charges.
Writing Names for Binary Ionic
Compounds
1.Write the name of the positive ion first.
2.Write the root of the negative ion’s name.
3.Change the ending to -ide.
Use the ion cards to write formulas
for and name binary ionic
compounds
1. sodium and chlorine2. calcium and chlorine3. aluminum and chlorine
Na 1+ Cl 1-
Formula: NaCl
Name of compound: sodium chloride
sodium ion chloride ion
Ca 2+
Cl 1-
Cl 1-
Formula: CaCl2
Name: Calcium Chloride
Al 3+
Cl 1-
Cl 1-
Formula: AlCl3
Name: Aluminum Chloride
Cl 1-
Polyatomic IonsA group of atoms that shares a common ionic charge.
Polyatomic ions must be memorized --- there’s no way around it!
See the chart of common ions.
Examples of some polyatomic ions:
Ammonium ion: NH41+
Nitrate ion: NO31-
Nitrite ion: NO31-
Hydroxide ion: OH1-
Sulfate ion: SO42-
Carbonate ion: CO32-
Phosphate ion: PO43-
Using the Ion Cards with
Polyatomic Ions
Na 1+NO3
1-
Sodium ion Nitrate ion
Chemical Name: sodium nitrate
Chemical Formula: NaNO3
NH4 1+
Ammonium ion
NH4 1+
Ammonium ion
SO42-
Sulfate ion
Chemical Name: ammonium sulfate
Chemical Formula: (NH4)2SO4
NH4 1+
Ammonium ion
NH4 1+
Ammonium ion
PO43-
Phosphate ion
Chemical Name: ammonium phosphate
Chemical Formula: (NH4)3PO4
NH4 1+
Ammonium ion
Ca 2+
calcium ionNO3 1-
Nitrate ion
NO3 1-
Nitrate ion
Chemical Name: calcium nitrate
Chemical Formula: Ca(NO3)2
Roman Numerals are used with elements
that have more than one common
oxidation number. (This includes most of the transition elements)
Examples:
CuBr2 is named Copper (II) bromide
PbCl2 is named Lead (II) chloride
EXCEPTIONS: Roman Numerals are NOT
needed for silver, cadmium, and zinc:
These transition elements ALWAYS have the following
oxidation numbers: Ag+ Cd2+, Zn2+
Examples:AgBr is named silver bromide, and NOT silver (I) bromide, because silver always has a 1+ oxidation number.
The same is true for compounds containing Cadmium or Zinc. (Cd and Zn are always 2+)
Some Special Ions:Copper (I) and (II) = Cu+ and Cu2+
Iron (II) and (III) = Fe2+ and Fe3+
Chromium (II) and (III) = Cr2+ and Cr3+
Lead (II) and (IV) = Pb2+ and Pb4+
Write names for:
1.FeS
2.CuCl
3. PbBr4
Check your work:
1.Iron (II) sulfide2.Copper (I) chloride
3.Lead (IV) bromide
Write formulas from the following
names:
1.Lead (II) bromide2.Chromium (II) sulfide3.CuI copper (II) iodide
Check your work:
4.PbBr2
5.CrS6.CuI2
Ionic CompoundsResult from the formation of ionic bonds.
Exist usually between a metal and a nonmetal
Are fun to name and write formulas for once you know the rules!
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