Transcript Chemical Bonds

Chemical Bonds
Chapter 20
Chemical Bonds
Section 1 Stability in Bonding slides 3-22
Section 2 Types of Bonds slides 23-48
Section 3 Writing Formulas & Naming
Compounds slides 49-84
1- Stability in Bonding
What You’ll Learn:
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About elements in a compound
Chemical formulas
How electric forces help form compounds
Why a chemical bond forms
Do compounds look like their
elements?
Elements can combine with others in a
chemical reaction to form compounds.
Do compounds look like their
elements?
Elements can combine with others in a chemical
reaction to form compounds.
When Cu, S & O combine, they produce a blue
solid, copper sulfate.
Do compounds look like their
elements?
Elements can combine with others in a
chemical reaction to form compounds.
When Cu, S & O combine, they produce a
blue solid, copper sulfate.
Cu shiny, copper metal, S yellow solid, O
colorless, odorless gas
Do compounds look like their
elements?
Cu shiny, copper metal, S yellow solid, O
colorless, odorless gas
When elements combine they produce
compounds with their own special
properties.
Formulas
A chemical
formula tells
what elements
are in a
compound &
how many
atoms of each
element are in
one unit of the
compound.
Name
Chemical
name
formula
Sand
Silicon
dioxide
Si O2
Milk of
Magnesium Mg
magnesia hydroxide (OH)2
Cane
sugar
Sucrose
C12H22
O11
vinegar
Acetic acid CH3COO
H
Atomic Stability
Protons positive & electrons negative
charge.
These opposite electric forces attract
each other pulling the atoms together to
form compounds.
Electron Distributions Into Shells
for the First Three Periods
Why do atoms form compounds?
Look at your periodic table. Notice the six
elements in Group 18, the noble gases.
Atoms of the noble gases almost never
combine to form compounds because they
are so stable (full).
Their compounds are less stable than the
original atoms.
Why are the noble gases different?
Lewis Dot Diagrams of Selected
Elements
Why are the noble gases different?
The number of electrons in the outer energy
level of an atom determines if that atom will
combine to form a compound.
What makes an atom stable?
An atom is chemically stable when it has
a complete outer energy level.
If an atom is chemically stable. It does not
easily form compounds with other atoms.
What elements have incomplete
outer energy levels?
None of the elements in Groups 1 through 17
have full outer energy levels. These elements
are more stable when they form compounds.
How do atoms become more
stable?
Atoms without a stable outer energy level
can do one of three things to complete
their outer level:
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Gain electrons
Lose electrons
Or Share electrons with other atoms that
have incomplete outer levels. This way, each
atom becomes more stable.
How do atoms become more
stable?
How do atoms become more
stable?
Sodium has one outer electron & chlorine
has seven.
When these two elements combine,
sodium gives its outer electron to chlorine
which now has eight electrons in its outer
level.
The next energy level of sodium is also full
& completely stable.
What is another way atoms can
become stable?
For the compound water, H2O, each
hydrogen shares an electron from an
oxygen to complete its outer level.
Oxygen shares each of the H atoms’
electrons to complete its outer level.
The compound water is more stable than
either a hydrogen atom or an oxygen
atom.
What is another way atoms can
become stable?
An attractive force forms when atoms gain,
lose, or share electrons to make a
compound.
A chemical bond is the force that holds
atoms together in a compound.
Atoms
Become more stable by:
They can do this by:
Atoms
Become more stable by:
Completing their outer
energy level
They can do this by:
Gaining electrons
Losing electrons
Sharing electrons
2- Types of Bonds
What You’ll Learn:
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What ionic bonds are
What covalent bonds are
What particles are produced by ionic &
covalent bonding
About polar & nonpolar covalent bonds
Gain or Loss of Electrons
Atoms gain or lose electrons to meet the
standard of a full energy level.
Gain or Loss of Electrons
Atoms gain or lose electrons to meet the
standard of a full energy level.
When an atom gains or loses an electron,
it becomes an ion.
Gain or Loss of Electrons
Atoms gain or lose electrons to meet the
standard of a full energy level.
When an atom gains or loses an electron,
it becomes an ion.
An ion is a charged particle because it
has either more or fewer electrons than
protons
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More electrons than protons, ion is negative
More protons than electrons, ion is positive
What are some common
compounds?
The electric forces between + and –
particles hold compounds together.
What are some common
compounds?
The electric forces between + and –
particles hold compounds together.
Many common compounds form by
gaining or losing just one electron from
Group 1 & Group 17 elements.
What are some common
compounds?
The electric forces between + and –
particles hold compounds together.
Many common compounds form by
gaining or losing just one electron from
Group 1 & Group 17 elements.
Examples: sodium chloride, sodium
fluoride, potassium iodide
How is potassium iodide formed?
K
I
[K]+ [ I ]
An atom of potassium has one electron in its outer
level which it loses becoming a positive (K+) ion.
How is potassium iodide formed?
K
I
[K]+ [ I ]
An atom of potassium has one electron in its outer
level which it loses becoming a positive (K+) ion.
When iodine reacts with potassium it becomes a
negative iodide ion (I-).
How is potassium iodide formed?
K
I
[K]+ [ I ]
An atom of potassium has one electron in its outer
level which it loses becoming a positive (K+) ion.
When iodine reacts with potassium it becomes a
negative iodide ion (I-).
An ionic compound forms when two or more ions
combine to become neutrally charged.
The Ionic Bond
An ionic bond is the force of attraction between a
positive ion & a negative ion in an ionic compound.
In an ionic compound, one atom gives up electrons & the
other atom takes them so that the compound stays neutral.
Mg
Cl
Cl
[ Cl ]-Mg+2[ Cl ]-
Magnesium+2 chlorine atoms =Magnesium Chloride
The Ionic Bond
In this case, the magnesium atom has 2 electrons
to give; however, a chlorine atom can only use 1
so it takes 2 chlorine atoms to rake the two
electrons from Mg & combine to form the ionic
compound magnesium chloride.
Mg
Cl
Cl
[ Cl ]-Mg+2[ Cl ]-
Magnesium+2 chlorine atoms =Magnesium Chloride
Does an ionic compound have a
charge?
It’s neutral because the sum of the
charges on the ions is zero.
The total number of electrons and protons
stays the same.
Ionic bonds usually form when a metal
bonds with a nonmetal.
Elements on the far left of the PT tend to
form ionic bonds with elements on the far
right.
Sharing Electrons
Some atoms of nonmetal elements
become more stable when they share
electrons.
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Group 14 elements have 4 outer electrons
Must gain or lose 4 e- to be stable
Requires lots of energy for that many
Ions hold remaining e- more tightly after each
loss so even more energy needed to remove
another---meaning it’s easier to share e-
Sharing Electrons
Some atoms of nonmetal elements
become more stable when they share
electrons.
A covalent bond is the force of attraction
between two atoms that share electrons.
Sharing Electrons
Some atoms of nonmetal elements
become more stable when they share
electrons.
A covalent bond is the force of attraction
between two atoms that share electrons.
A molecule is the neutral particle that
forms when atoms share electrons.
How are single covalent bonds
formed?
When 2 atoms share
2 e-, 1 from each
atom in the covalent
bond
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How are single covalent bonds
formed?
When 2 atoms share
2 e-, 1 from each
atom in the covalent
bond
There are 2 single
covalent bonds in
water.
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How are single covalent bonds
formed?
When 2 atoms share
2 e-, 1 from each
atom in the covalent
bond
There are 2 single
covalent bonds in
water.
In each single bond, a
H atom & an O atom
each give 1 e- which
the atoms share
becoming more
stable.
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What are multiple bonds?
A covalent bond can
have more than 2
electrons.
Each N atom has 5 ein outer energy level;
needs 3 to be stable.
Share 3 pairs of e- to
form triple bond
making 8 e- in outer
energy level. N2
www.chem.lsu.edu/
grandinetti.org/.../LewisDot/assets/N2
.gif
What are multiple bonds?
Space filling
model of
carbon
dioxide
A double bond is 2
pairs of electrons
shared between 2
atoms. In CO2 the C
atom shares 2 e- with
1 O atom & 2 e- with
the other O atom. In
return each O shares
2 e- with the C so that
all 3 have 8 e- in outer
energy level.
Recognize covalent compounds
Covalent bonds form between nonmetals.
Nonmetals are found in the upper righthand corner of the PT.
Many covalent compounds are liquids or
gases at room temperature.
Are electrons always shared
equally?
Not always because the positive charge in
one nucleus can be stronger than that of
another smaller atom.
If a shared electron is closer to one nuclei
it may be held more strongly.
Nuclei with a greater positive charge
attract electrons more strongly.
What is an example of unequal
electron sharing?
Hydrogen chloride HCl is
an example of unequal esharing. When mixed
with water it becomes
hydrochloric acid. Cl
atom attracts e- in the
bond more strongly than
the H atom. Cl has
partial negative charge δ_
& H has a partial positive
charge δ+.
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What are polar & nonpolar
molecules?
In water, oxygen has
a stronger attraction
for the bonding egiving the O a partial
negative charge & the
H a partial negative
charge. A polar
molecule has a
slightly + end & a
slightly – end, but the
molecule is neutral
What are polar & nonpolar
molecules?
In a nonpolar
molecule, electrons
are shared equally
with no partial
charges or oppositely
charges ends.
3- Writing Formulas & Naming
Compounds
What You’ll Learn:
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How to determine oxidation numbers
How to write formulas & names for ionic
compounds
How to write formulas & names for covalent
compounds
Binary Ionic Compounds
A binary compound is a compound made of
two elements; for example, potassium iodide, a
compound added to table salt.
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Are electrons gained or lost?
Before you can correctly write a formula of
a compound, you need to know which
elements combine & what happens to their
electrons.
Are electrons gained or lost?
Before you can correctly write a formula of
a compound, you need to know which
elements combine & what happens to their
electrons.
The oxidation number of an element tells
you how many electrons an atom gains,
loses, or shares to become stable.
Are electrons gained or lost?
Before you can correctly write a formula of
a compound, you need to know which
elements combine & what happens to their
electrons.
The oxidation number of an element tells
you how many electrons an atom gains,
loses, or shares to become stable.
The charge on the ion in an ionic
compound is the same as its oxidation
number.
Oxidation Numbers
How are oxidation numbers related
to the periodic table?
The numbers in the
columns are the
oxidation numbers for
the elements in that
family. Compounds
from the center
elements can have
more than one
oxidation number
indicated by a roman
numeral in compound
names.
How many positive & negative ions
must a formula have?
Ionic compounds are neutral even though
the ions in them have charges.
Their formulas must balance charges.
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Na- Cl+ combine to form NaCl sodium chloride
Ca+2 & F- combine to form CaF2 calcium
fluoride. Here it requires two negative fluoride
ions to neutralize the positive 2 calcium ion.
How do you find the correct
subscripts?
Sometimes you need math skills to write a
formula correctly.
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Aluminum oxide oxidation number Al+3 O-2
You must find the Least Common Multiple of 3
& 2 to balance the charges.
LCM=6 so the correct formula aluminum oxide
is Al2O3 so that +6 neutralizes -6
How do you write the formula of an
ionic compound?
Rule 1- Write the symbol of the positively
charged ion first. Sometimes ions are
polyatomic, ex. Ammonium or NH4+. All
metals form ions with a positive charge.
How do you write the formula of an
ionic compound?
Rule 1- Write the symbol of the positively
charged ion first. Sometimes ions are
polyatomic, ex. Ammonium or NH4+. All
metals form ions with a positive charge.
Rule 2-Write the symbol of the ion with the
negative charge. Nonmetals other than
hydrogen form negative ions. All
polyatomic ions except NH4+ have a
negative charge.
How do you write the formula of an
ionic compound?
Rule 2-Write the symbol of the ion with the
negative charge. Nonmetals other than
hydrogen form negative ions. All
polyatomic ions except NH4+ have a
negative charge.
Rule 3-The number of the charge ( without
the sign) of one ion becomes the subscript
of the other ion.
How do you write the formula of an
ionic compound?
Write the formula for lithium nitride.
How do you write the formula of an
ionic compound?
Write the formula for lithium nitride.
Lithium, from Group 1, is a 1+ ion so it’s
first.
How do you write the formula of an
ionic compound?
Write the formula for lithium nitride.
Lithium, from Group 1, is a 1+ ion so it’s
first.
Nitrogen, from Group 15 has 3- charge.
How do you write the formula of an
ionic compound?
Write the formula for lithium nitride.
Lithium, from Group 1, is a 1+ ion so it’s
first.
Nitrogen, from Group 15 has 3- charge.
Li N but 1+ 3- don’t neutralize.
How do you write the formula of an
ionic compound?
Write the formula for lithium nitride.
Lithium, from Group 1, is a 1+ ion so it’s
first.
Nitrogen, from Group 15 has 3- charge.
Li N but 1+ 3- don’t neutralize.
Li3N balances the ions for a correct
formula.
Write the formula for calcium
chloride.
Write the formula for calcium
chloride.
Ca from Group 2 & Cl from Group 17
Write the formula for calcium
chloride.
Ca from Group 2 & Cl from Group 17
Ca+2
Cl -1
Write the formula for calcium
chloride.
Ca from Group 2 & Cl from Group 17
Ca+2
Cl -1
Ca Cl2
How do you write the name of a
binary ionic compound?
When you know the formula, you can write
the name using these rules:
Rule 1-Write the name of the positive ion.
Rule 2-Check to see if it can have more
than one oxidation number. Look at the
formula, pick the charge of the positive ion
that balances the charge. Write the
positive ion’s symbol along with the correct
roman numeral in parentheses.
How do you write the name of a
binary ionic compound?
Rule 3- Write the root name of the
negative ion. The root is the first part of
the element’s name. Ex. Chlor- or oxRule 4- Add the ending –ide to the root
name. Ex. Chloride or oxide.
How do you use these rules?
Write the name for the compound CuCl.
How do you use these rules?
Write the name for the compound CuCl.
Cu can have1+ or 2+ charge. Cl of Group
17 has the oxidation number -1.
How do you use these rules?
Write the name for the compound CuCl.
Cu can have1+ or 2+ charge. Cl of Group
17 has the oxidation number -1.
Copper (I) chloride
Compounds with Complex Ions
The formula for baking soda is NaHCO3.
It is made of more than 2 elements.
These compounds have polyatomic ions,
a charged group of atoms covalently
bonded together.
The polyatomic ion in baking soda is the
bicarbonate or hydrogen carbonate ion,
HCO3-.
Polyatomic Ions
Charge
1+
Name
ammonium
Formula
NH4+
1-
Acetate
Chlorate
Hydroxide
nitrate
Carbonate
sulfate
C2H3O2ClO3OHNO3CO32SO42-
phosphate
PO4-
23-
How do you name a complex
compound?
First write the name of the positive ion.
Then find the name of the negative ion
using the table if it is polyatomic.
K2SO4 is
Sr(OH)2 is
How do you name a complex
compound?
First write the name of the positive ion.
Then find the name of the negative ion
using the table if it is polyatomic.
K2SO4 is potassium sulfate.
Sr(OH)2 is strontium hydroxide.
How do you write the formula of a
complex compound?
Use the rules for a binary formula, but add
one more thing. If it needs more than one
polyatomic ion, put parentheses around
the ion’s formula before you write the
subscript.
Write the formula for barium chlorate.
How do you write the formula of a
complex compound?
Use the rules for a binary formula, but add
one more thing. If it needs more than one
polyatomic ion, put parentheses around
the ion’s formula before you write the
subscript.
Write the formula for barium chlorate.
Ba(ClO3)2
Compounds with added water
A hydrate is a compound that has water
chemically attached to its ions & written
into its formula.
Compounds with added water
A hydrate is a compound that has water
chemically attached to its ions & written
into its formula.
If you evaporate a solution of cobalt
chloride, pink crystals form. The crystals
have 6 water molecules for each unit of
cobalt chloride. Formula is CoCl2 · 6H2O
Naming Binary Covalent
Compounds
Covalent compounds form between
nonmetals & some can form more than
one compound such as nitrogen & oxygen.
N2O, NO, NO2, and N2O5 would all be
nitrogen oxide according to the earlier
rules.
We use prefixes to distinguish between
them.
How are prefixes used to name
covalent compounds?
Drop the last vowel of
the prefix when the
second element
begins with a vowel.
N2O dinitrogen oxide
N2O5 dinitrogen
pentoxide
1
Mono-
2
Di-
3
Tri-
4
Tetra-
5
Penta-
6
Hexa-
7
Hepta-
8
Octo-