Transcript Unit 5 : Ionic and Metallic Bonding

Ionic and
Metallic Bonding
Concepts to Master
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Understand the difference between an
element and a compound.
Understand ionic bonding and the
properties of ionic compounds
Realize the differences between the ionic
bonding and metallic bonding.
Write chemical formulas for ionic
compounds using oxidation number.
Learn the polyatomic ions.
Use polyatomic ions when writing
chemical formulas.
Learn two methods for balancing
chemical formulas: stacking and crisscross.
Understand how and why Lewis dot
diagrams work for ionic compounds.
Compare and contrast the Lewis dot
diagrams for atoms and ions.
Learn the definition of exothermic and
endothermic.
Apply the above definitions to chemical
bonding
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Learn how ions and conductivity are
related.
How does ionization energy relate to
bond formation?
How are ions in a compound held
together?
How many atoms are in a binary
compound?
How many atoms are in a ternary
compound?
If a compound is ternary, what type of ion
does it usually contain?
Be able to calculate formula mass.
Be able to calculate percent hydration
when given experimental data or the
chemical formula.
Be able to calculate percent composition
when given experimental data or the
chemical formula.
What is a sea of mobile electrons and in
what types of substances is it found?
Vocab
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Alloys
Anhydrate
Anion
Atom
Binary
Cation
Chemical bond
Chemical properties
Compound
Conductivity
Electrostatic attraction
Element
Endothermic
Exothermic
Formula mass
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Hydrate
Ionic
Ionic Charge
Ionization energy
Ions
Lewis dot structure
Metallic
Mobile electrons
Oxidation number
Physical properties
Polyatomic ion
Ternary
• Labs
– Exo / Endo Rxns
– Percent Hydration
– Determining oxidation number
Review
Elements versus Compounds
• Atoms are the smallest
particle of an element that
can exist.
• Elements are substances
that cannot be separated
into simpler substances.
• A compound is a
substance formed when
two or more elements are
chemically joined. Like
atoms, they are
NEUTRAL.
Compounds
• The smallest unit of a substance that can exist
alone and still retain the properties of that
substance.
• These properties are different than the
properties of the atoms alone.
+
Properties of
Mg?
=
Properties of
Cl?
Properties of
MgCl?
• Atoms are Chemically Bonded and can only be
separated by a chemical process.
What is a Chemical Bond?
• A chemical bond is an attraction between atoms
brought about by a sharing of electrons between
two atoms or a complete transfer of electrons.
• Bonding occurs so atoms can satisfy the octet
rule.
• There are three types of chemical bonds:
– Ionic
– Covalent
– Metallic
Forming Bonds is Exothermic
When the atoms form a bond they become lower in
energy and the system is more stable. The energy
saved by moving to a more stable situation is
released as heat. The more energy released the
greater the compound’s stability.
Breaking Bonds is Endothermic
Since atoms form bonds to become more stable, energy is
required to break them apart. When more energy is required to
break the bond, the more stable the bond is.
Chemical Equations
• Bond Formation = exothermic
• Breaking of Bond = endothermic
2 KClO3 --> 2 KCl + 3 O2
Exo or Endo ?
Exo or Endo ?
Once bonds are formed…
• compounds are
made.
• and they are written
as chemical formulas
– represent the
composition of a
compound
• group of elemental
symbols
• possibly subscript
numbers
Formula
Composition
NaCl
Total of 2 elements
in each compound.
1 sodium and 1
chlorine
Total # of atoms =
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NH4OH
Total # of atoms =
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KSCN
Total # of atoms =
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Total of 3 elements
in each compound.
1 oxygen, 5
hydrogen, and 1
nitrogen
Total of 4 elements
in each compound.
1 potassium, 1
sulfur, 1 carbon, 1
nitrogen
• When metallic atoms
react…
– They lose electrons to form
cations.
– They acquire an electron
configuration that satisfies
the octet rule.
– Their radii decrease.
– They want to give electrons
away so electronegativity
is low.
• When non-metal
atoms react…
– They gain electrons to form
anions.
– They acquire an electron
configuration that satisfies
the octet rule.
– Their radii increase.
– They want electrons so
electronegativity is high.
Which color is the cation?
Which color is the anion?
When Metals lose electrons,
they get smaller!
When Nonmetals gain electrons,
they get bigger!
Cation is +
Anion is -
Ionic Compounds
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Complete TRANSFER of electrons from METAL to NONMETAL.
– Metal loses electron to become cation.
– NonMetal gains electron to become anion.
– An electrostatic attraction occurs between the + cation and – anion. (Opposites
attract.)
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Properties (Physical or Chemical?)
– Crystals / salts have a lattice formation with repeating pattern
– Very hard solids
– Not malleable (brittle), shatters
– Easily dissolve in water
– Conduct electricity when dissolved in water and when molten
– Do not conduct electricity as solids
– High melting point: What does this tell you about chemical bond energy?
Ionic Compounds
ZnS
CsCl
Are they solid, liquid, or gas?
How do you know?
Na and Cl
Na
(Metal)
Cl
(non-Metal)
Electron configuration
is?
# of valence electrons?
How many will be lost
or gained to achieve an
octet?
Lewis Dot Diagram
Lewis Dot Formula:
Compound Formula:
Ca and Cl
Ca
(Metal)
Cl
(non-Metal)
Electron
configuration is?
# of valence
electrons?
How many will be
lost or gained to
achieve an octet?
Lewis Dot Diagram
Lewis Dot Formula:
Compound Formula:
Al and O
Al
(Metal)
O
(non-Metal)
Electron
configuration is?
# of valence
electrons?
How many will be
lost or gained to
achieve an octet?
Lewis Dot Diagram
Lewis Dot Formula:
Compound Formula:
Lewis Dot Diagram for Ionic Compounds
– Brackets required
– Each bracket must show charge
– Metallic brackets will have no electron dots
– Non-metallic brackets will show 8 electrons dots
KP
– Stack the positive and negative brackets
– Examples:
NaI
AlCl3
Na2S
CaF2
RbBr
K3P
3
Using oxidation numbers to
determine compound formulas
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Oxidation numbers are used to determine the ratio in which elements combine
to form compounds.
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Cations
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Metals
Anions
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Non-metals
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Chemical formulas are composed of a positive half and a negative half.
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Sodium Chloride is a compound you know to have a formula of NaCl.
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The element with the positive oxidation number is always written first: Na
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The element with the negative oxidation number is always written second: Cl
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The total of the oxidation numbers in a compound must equal zero.
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Na oxidation number is +1 and Cl is -1.
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With one Na and one Cl, the total is 0.
Steps
What is the formula of Calcium Nitride?
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Identify the symbols of each part of the name.
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Calcium symbol is Ca.
b)
Nitride symbol is N.
Identify the charge for each.
a)
Calcium is +2.
b)
Nitride is -3.
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Balance the charges.-Criss-cross method
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Write the symbol beginning with the symbol that is first in the
name and include the subscript after each symbol Ca3N2.
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Check to be sure that the subscript numbers are “reduced”.
Binary compounds
• Contain only 2 elements
• Write formulas for the following:
– Potassium and sulfur
– Rubidium and sulfur
– Magnesium and chlorine
– Sodium and nitrogen
Binary Cmpds with Roman
Numerals
• Many of the transition metals have more than 1 oxidation
number.
• The name of the compound contains a roman numeral to
indicate which oxidation number was used to determine
the compound formula.
• Examples:
• Copper (II) sulfide
• Iron (III) oxide
• Mercury (II) iodide
• Tin (IV) fluoride
Polyatomic Ions
• Polyatomic ions are charged group of
atoms.
• Contain BOTH ionic and covalent bonds
• Act as a single unit.
• Use parentheses when more than one is
present in the compound formula.
• Use Table E on the reference booklet.
Ternary Compounds
• Contain 3 or more different elements
• Often a polyatomic ion is present.
– Na2CO3
– KClO3
– LiOH
– CuSO4
• Writing Formulas for Ternary Compounds
•Ammonium hydroxide
Calcium phosphate
Potassium oxalate
Conductivity and IONS
• Conductivity is the ability of a material to
conduct electric current.
• Ions are charged atoms so they conduct
electricity when dissolved in water.
• Conductivity is proportional to the number
of ions in solution.
• Increasing the number of ions in a solution
increases the solution’s conductivity.
Conductivity and IONS
Ionic
# of
Compound Cations
# of
Anions
Total # of
IONS
KCl
Al2(SO4)3
MgBr2
AgOH
Which one will have the GREATEST Conductivity?
Naming Ions
• Metals: name of metal + “ion”.
• Transition Metals: name of
metal + (charge of metal) +
“ion”.
• Non-metals: root of non-metal +
“-ide“.
• Polyatomic ions: name on
Reference Table E
Hints that you have a polyatomic ion:
1. 3 or more capital letters in the compound
(ternary)
2. Parenthesis are present
3. Compound’s name ends in “ate” or “ite”.
Exceptions are hydroxide, peroxide, and
cyanide
• Examples:
1. Cu+
2. Mg2+
3. F4. OH5. Fe3+
• Answers:
1. Copper (I) ion
2. Magnesium ion
3. Fluoride ion
4. hydroxide ion
5. iron (III) ion
Naming Compounds
1. Name the positive part (this always comes first).
1. If the positive part is a monatomic cation (a single symbol positive ion) - name the
element.
2. If the positive part is a polyatomic ion (Table E) - name it.
2. Name the negative part (this is the last part of the compound).
1. If the negative part is a monatomic anion (a single symbol negative ion) - take the root
of the element and add "ide."
2. If the negative part is a polyatomic ion (Table E) - name it.
3. Check to see if a Roman Numeral is needed:
1. A Roman numeral is not needed if the positive part has only one positive oxidation state
on the periodic table. (With only one positive oxidation state, there is only one possible
combination of how the elements will bond together.)
2. A Roman numeral is needed if the positive part has two or more positive oxidation
states on the periodic table. (With more than one positive oxidation state, there are as
many combinations of how the elements will bond together as there are positive
oxidation states.)
4. A Roman Numeral is the value of the Positive Oxidation State on one cation.
1. It is not a subscript.
2. It is not the total positive charge.
Practice Naming
• Ga2(SO3)3
• Al2(CO3)3
• Ba(OH)2
• FeF3
• Li3N
• NH4Cl
In the old days…
• Metals
– "ous" is added to the root of
the element for the smaller
oxidation state.
– "ic" is added to the root of
the element for the larger
oxidation state.
• Examples:
– Copper
• Cuprous = Cu+1
• Cupric = Cu+2
– Iron
• Fenous = Fe+2
• Ferric = Fe+3
Cupric Bromide = CuBr2
Formula Mass
• The formula mass is the total mass of all the atoms
within the formula.
• When a formula contains polyatomic ions, the number
of atoms inside the brackets are multiplied by any
subscript immediately behind the brackets.
Determine the Formula Mass for
each of the following.
KBr
LiOH
NaNO3
Ba(OH)2
(NH4)2O
CaCO3
Hydrate vs Anhydrate
• Hydrates contain water.
– Water is “associated” with the chemical.
– The water is not chemically bound because it can be
removed by simply heating.
• Anhydrates contain NO water. They are
dehydrated.
MgBr2 ·6 H2O(s) + HEAT → MgBr2 (s) + 6 H2O(g)
Hydrate
Anhydrate
“Hydrated” Formula Mass
• Sometimes when ionic crystals form, water becomes a part of the
crystal structure.
– water of hydration
– the crystals are called "hydrates" or "hydrated salts“
– Formulas for hydrates always include a dot separator, followed by
the number of water molecules attached,
• CuSO4●5H2O
• FeCl2●4H2O
% Hydration - Experimental
When a 1.000 g sample of CuSO4 ·5 H2O(s) was heated so that the waters of hydration
were driven off, the mass of the anhydrous salt remaining was found to be 0.6390 g.
What is the experimental value of the percent water of hydration?
CuSO4 ·5 H2O(s) + HEAT
1.000 g
→
CuSO4 (s) + 5 H2O (g)
0.6390 g
1. Find the difference between the mass of hydrate before heating and the mass of the
anhydrate after heating. The difference is the mass of water lost.
1.000 g - 0.6390 g = 0.3610 g
2. Dividing the mass of the water lost by the mass of hydrate used is equal to the fraction
of water in the compound. Multiplying this fraction by 100 gives the percent water in
the hydrate.
(0.3610 g /1.000 g)(100) = 36.10%
% Hydration – Chemical Formula
The theoretical (actual) percent hydration (percent water) can be calculated from the
formula of the hydrate by dividing the mass of water in one unit of the hydrate by the
total mass of the hydrate and multiplying this fraction by 100.
What is the percent water in copper(II) sulfate pentahydrate, CuSO4 ·5 H2O?
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Calculate the formula mass.
2. Divide the mass of water in one unit of the hydrate by the total mass of the hydrate and
multiply this fraction by 100.
Percent hydration = (90.10 g /249.72 g)(100) = 36.08%
Determine the % hydration of…
• Na2SO4•10H2O
• CaCl2•6H2O
% Composition
• The % composition of each element is the mass of that
element (ionic or covalent) divided by the total mass of
the compound multiplied by 100.
• What is the % composition of sulfur in sodium sulfide?
– Determine formula mass.
– Divide formula mass by the mass of sulfur and multiply by 100.
• (32.07 / 78.05) x 100 = 41.09 % sulfur
Determine %
Composition of the
underlined element
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Sn3P4
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AcF3
Determine %
Composition of each
element
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CaCO3
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KBr
Metallic Bonding
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The electrons can move freely within these
molecular orbitals, and so each electron becomes
detached from its “parent atom”.
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The metal is held together by the strong forces of
attraction between the positive nuclei and the
delocalized electrons.
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This is sometimes described as "an array of
positive ions in a sea of mobile electrons".
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Is a metal made up of atoms or ions? It is made of
atoms.
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Each positive center in the diagram represents all
the rest of the atom apart from the outer electron,
but that electron hasn't been lost - it may no longer
have an attachment to a particular atom, but it's
still there in the structure. Sodium metal is
therefore written as Na (not Na+).
Metallic Bonds
• Positive ions immersed in a sea of electrons
– Low ionization energies cause electrons to be loosely
held
– So valence electrons move among the atoms and
around the many kernels
– “Mobile sea of electrons”
• Properties
– Good conductors of electricity and heat as a solid or
liquid
– Moderately to very hard (Au vs Zr)
– Lustrous since electrons absorb and emit light as they
move around
– Malleable (not brittle)
– High melting point
Metallic Bonds
Alloys
• Material that contains
more than one element
and has the characteristic
properties of metals
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Brass
– 67% Cu
– 33% Zn
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Stainless Steel
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80.6% Fe
0.4% C
18% Cr
1% Ni
Gold (14K)
– 58% Au
– 42% Cu
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Sterling Silver
– 92.5% Ag
– 7.5% Cu
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Bronze
– 88% Cu
– 12% Sn
Check
• Draw the Lewis Dot diagrams for
aluminum bromide
• Al+3 Br-1
• Criss cross AlBr3
• [Al] +3
[Br] -1
[Br] -1
[Br] -1
DOTS?
check
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Name BaH2
barium hydride
Name Mn2(CrO4)3
Manganese (III) chromate
check
• Determine the % composition for all of the
elements in barium hydroxide using its
chemical formula.
• Ba(OH)2
• FW = 137.33+2(1)+2(16) = 171.33
• Ba : (137.33/171.33)x100 = 80.2%
• O : (32/171.33)x100 = 18.7%
• H : (2/171.33) x100 = 1.1%