Polyatomic ions
• Poly = many
• Atomic = atoms
• Entire group of atoms is an ion with
a positive or negative charge.
• Examples:
Sulfate ion
SO4 2-
Carbonate ion
CO3 2-
S
C
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Memorize These Polyatomic Ions
- 1 charge
nitrate
NO3nitrite
NO2hydroxide OHbromate
BrO3perchlorate ClO4chlorate
ClO3-chlorite
ClO2hypochlorite ClOcyanide
CNpermanganate
MnO4hydrogen sulfate
HSO4hydrogen carbonate HCO3acetate
C2H3O2or CH3COO_+ 1 charge
Ammonium
NH4+
-2 charge
sulfate
SO42sulfite
SO32carbonate CO32chromate
CrO42dichromate Cr2O7 2oxalate C2O42peroxide
O22hydrogen phosphate HPO42-
-3 charge
phosphate PO43arsenate AsO43-
+2 charge
dimercury or mercury (I)
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Hg22+
2
Atoms and Bonding
• A chemical bond is an attractive force that holds
the atoms of a compound together.
• Atoms of elements with unfilled outer energy
levels can form bonds.
• When atoms form chemical bonds, they fill their
outer energy levels with electrons and become
more stable.
• We will study three types of chemical bonds:
ionic, covalent and metallic bonds.
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Chemical Bonds
• Attractive force that holds atoms or ions
together.
• An atom with an unfilled outer electron
shell is likely to bond with another atom.
• Noble gases have filled outer shells. They
are unlikely to form bonds readily.
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Stability and Bonding
• Matter in lowest energy state is more stable
than higher energy state.
• More stable = less likely to change.
• Filled outer shell = more stable.
• How can an atom fill its unfilled outer
shell?
– With electrons from another atom
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Three Kinds of Bonds
1. Ionic
•
•
•
Electrons transferred from atom to atom
Example: NaCl
Type of bonds in ionic compounds
2. Covalent
•
•
•
•
Electrons are shared.
Usually 2 atoms share a pair of electrons.
Example: C6H12O6
Type of bonds in molecular compounds.
3. Metallic
•
•
•
Electrons are shared between many atoms.
Many atoms share many electrons.
Example: Pure Ag Mullis
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Ionic Bonding
• Like loaning your friend your extra baseball
glove if you want to play ball:
– The friend is using your glove and you are not,
but
– Both of you benefit.
• Ionic bonds:
– One atom uses the electron from another atom.
– Both benefit because both are more stable.
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More on Ionic bonds
• The atom that gives up the electron =
positive ion.
• The atom that accepts the electron =
negative ion.
• The ions are attracted to each other
because they have opposite charges.
• AN IONIC BOND IS AN
ELECTROSTATIC ATTRACTION
BETWEEN OPPOSITELY CHARGED
IONS.
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Example of Ionic Bonding
• Chlorine and sodium
• Sodium atom
11 protons =
11 electrons =
Charge
11+
11 0
• Sodium ion
11 protons =
11 electrons =
Charge
Chlorine atom
17 protons = 17+
17 electrons = 17Charge 0
Chloride ion
11+
10 1+
17 protons = 17+
17 electrons = 18Charge
1-
Together, Na and Cl are attracted to each other and they
are electrically neutral. Mullis
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The Crystal Lattice
• 3-dimensional pattern that repeats itself
over and over again.
• Each ion is bonded with all oppositely
charged ions that directly surround it.
• NaCl forms a cube shape, called a bodycentered-cubic structure.
• There are 7 crystal shapes, determined by
how the ions are arranged in the lattice.
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Crystal growth
•
•
•
Crystals grow by adding ions to all sides.
They grow equally in all directions from
the outside.
Crystals form in 2 ways:
1. Solution containing a dissolved ionic
compound evaporates.
2. An ionic solid is heated until it melts, then
liquid is cooled. (Igneous rocks)
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Ions
• Alkali metals form ions with + 1 charge since they tend to lose an
electron.
• Halogens tend to form ions with –1 charge since they tend to gain an
electron.
• Positive ions are smaller than atoms of the same element.
– Nucleus holds on to the remaining electrons (existing
happily in their filled outer shell).
Na
- 1 electron
Na+
• Negative ions are larger than atoms of the same element.
– More electrons means more repulsion .
– Cl- has radius of almost 2x the radius of Cl atom.
Cl
+ 1 electron
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Cl12
Ions, Continued
• When an ionic compound dissolves in
water, each ion is surrounded by water
molecules.
• Living things take up the ions dissolved in
water to use as nutrients.
• Water softeners replace Ca and Mg ions in
hard water with Na ions.
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• 19.2 Ionic Bonds
• An ionic bond forms when electrons are
transferred from one atom to another.
• An ionic bond is an electrostatic attraction
between ions that have opposite charges.
• Ionic bonds form between the atoms of metallic
and nonmetallic elements.
• The ions that make up ionic solids are arranged in
a three-dimensional structure called a crystal
lattice.
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• 19.3 Covalent Bonds
• A shared pair of electrons makes up a
covalent bond between two atoms.
• Covalently bonded atoms form either
molecules or network solids.
• Polyatomic ions, such as ammonium and
sulfate ions, are groups of covalently bonded
atoms with an overall charge.
• Metallic bonds occur in metals, where a sea
of shared electrons surrounds positive metal
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ions arranged in a lattice
structure.
Covalent Bonds
• shared pair of electrons
• Between 2 or more nonmetals
• Nonmetals have outer shells that
are at least ½ full.
• Molecules are formed with covalent
bonds ( …molecular compounds).
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Covalent Bonds again
• Molecules have definite size; they do not
keep growing like ionic solids.
• Example:
H
+
H Br
Br
H
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Br
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Octet Rule
• Chemical compounds tend to form so that each atom has
an octet of electrons in its highest occupied energy level.
• s orbital = 2 electrons when full
• p orbital = 6 electrons when full
• Orbitals which overlap for sharing feel full, since they
have 8 electrons. (6 + 2 = 8)
• Example: O (8 total electrons, 6 valence electrons)
O
___ ___ ___ ___ ___
O2 is O O
1s
2s
2p
4 shared electrons =
2 pairs = 2 bonds
O
___ ___ ___ ___ ___
1s
2s
2p
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Bond energy
• Bond energy is the energy required to break a
chemical bond and form neutral isolated
atoms.
• Units are kilojoules/mole (kJ/mol).
• Higher bond energy = shorter bond length
• H—F length is 92 pm, energy is 569 kJ/mol
• F—F length is 141 pm, energy is 159 kJ/mol
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Lewis structure and structural formula
• Lewis structures represent molecules with dots
and dashes
– Atomic symbol represents nucleus + inner electrons
– Dots represent electrons
– A dash represents a shared electron pair, or single
bond.
H—S—H
• A structural formula shows the kind
of bonds, but not unshared pairs of
electrons.
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H—S—H
20
Resonance structure
Resonate: To bounce, or alternate, back and forth
• The structure switches from one Lewis
structure to another
• One Lewis structure is not entirely accurate.
O
O
O
O
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O
O
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Metallic Bonds
• The valence electrons make up a “sea”
of electrons.
• Valence electrons do not belong to
individual atoms, so charge is positive.
(It’s like living in a commune.)
• Metals have high density because
lattice is tightly packed atoms.
• Metals conduct electricity because
electrons move freely.
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