Download Atoms in Combination: The Chemical Bond

Atoms in Combination:
The Chemical Bond
Trefil & Hazen
The Sciences
Chapter 10
Atoms bind together in
chemical reactions by the
rearrangement of electrons.
Outer electrons = “valence electrons”
Valent = combining power
Figure 8-13
The periodic table of the elements. The weights of the elements
increase from left to right. Each vertical column groups elements
with similar chemical properties.
Figure 8-13
The periodic table of the elements. The weights of the elements
increase from left to right. Each vertical column groups elements
with similar chemical properties.
Each shell can hold only a
limited number of electrons
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The innermost shell can hold 2;
the second and third shells, 8 each;
the fourth and fifth shells 18 each;
the sixth and seventh shells 32 each.
• Does this remind you of the periodic table?
Figure 8-13
The periodic table of the elements. The weights of the elements
increase from left to right. Each vertical column groups elements
with similar chemical properties.
Figure 8-14
A representation of electrons in a number of common atoms.
Figure 8-14
A representation of electrons in a number of common atoms.
Every object in nature tries to reach a
state of lowest energy.
• When atoms come together, the electrons
rearrange themselves to minimize the
potential energy in the system.
• This situation requires atoms to either
exchange or share electrons.
Most atoms adopt one of three
simple strategies to achieve a
filled outer shell: they give away
electrons, accept electrons, or
share electrons.
Chemical Bonds
• result from redistribution of electrons to
form a more stable electron configuration
between two or more atoms.
Al2O3
CO2
H2O
CaCl2 CH4
MgO
NaCl
NH3
Ionic Bond
Ionic Bond
• Sodium atom
• Loses one
electron
• Becomes a
sodium ion, Na+
• Stable [Ne]
• Chlorine atom
• Gains one
electron
• Becomes a
chloride ion, Cl• Stable [Ar]
Metals lose e- Nonmetals gain e-
Figure 10-1
Sodium, a highly reactive element, readily transfers its single valence
electron to chlorine, which is one electron shy of the “magic” number
18. The result is the ionic compound sodium chloride—ordinary table
salt. In these diagrams, electrons are represented as dots in shells
around a nucleus.
Courtesy Robert Capece
Figure 10-9
Individual salt crystals reveal a characteristic cube shape.
Figure 10-2
The atomic structure of a sodium chloride crystal consists of a
regular pattern of alternating sodium and chloride ions.
Figure 10-3
Calcium and chlorine neutral-atom electron configurations (left),
and their configurations after electrons have been transferred from
the calcium to the chlorine atoms (right).
Metallic bond – electrons are redistributed so
they are shared by all the atoms as a whole.
Figure 10-4
Metallic bonding, in which a bond is created by the sharing of
electrons among several metal atoms.
Naming ionic compounds with variable
charge transition metals…
• Fe3+ and O2• Fe2O3
• iron (III) oxide
• Sn 4+ and O2• SnO2
• tin (IV) oxide
Figure 10-5
Two hydrogen atoms become an H2 molecule by sharing each of
their electrons in a covalent bond. This bonding may be
represented schematically in a dot diagram (a), or by the merging
of two atoms with their electron clouds (b).
Covalent Bond
• Hydrogen atom
• Has one unpaired
valence electron
• Becomes stable by
sharing its outer
electron with one
of carbon’s [He]
• Carbon atom
• Has four unpaired
valence electrons
• Becomes stable by
sharing its lone
electrons with one
from hydrogen [Ne]
Covalent Bond
Figure 10-7
The water molecule and its polarity.
Bonding
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Ionic
Electron transfer
Metal loses eNonmetals gain eElectrostatic attraction
holds the crystal
together
• NaCl
• crystal
• Covalent
• Electron sharing
• Two nonmetals share
a pair of valence
electrons which orbit
both atoms, holding
them together
• H2O
• molecule
Chemical Reaction
• --the rearrangement of atoms that occurs
when substances undergo chemical change
• During a chemical reaction, a new material
is formed by this shuffling of atoms
• Bonds break, new bonds form
• Reactants  Products
Figure 10-13
In pictorial form, an oxidation reaction involves the transfer of
electrons to oxygen atoms. When natural gas (CH4) burns, it
combines with two oxygen molecules (O2) to form a molecule of
carbon dioxide (CO2) and two molecules of water (H2O).
Reactants  Products
• A chemical equation shows the material
about to react to the left of an arrow that
points to the newly formed materials.
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2Na + Cl2  2NaCl
2H2O2  2H2O + O2
Zn + 2HCl  ZnCl2 + H2
CH4 + 2O2  CO2 + 2H2O
Types of Chemical Reactions
• Synthesis
• A + B  AB
• Calcium + Oxygen  Calcium Oxide
• Ca + O2  CaO
Types of Chemical Reactions
• Decomposition
• AB  A + B
• CaCO3  CaO + CO2
• (Calcium carbonate yields calcium oxide
and carbon dioxide)
“Polyatomic Ions”
• Groups of nonmetals bonded together with an overall net
charge.
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ammonium
NH4 +
carbonate (CO3) 2hydroxide OHnitrate
NO3phosphate PO43sulfate
SO42CaCO3
H2SO4
NaOH
NH4NO3
Types of Chemical Reactions
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Single Displacement
A + BX  AX + B
Zn + HCl  ZnCl2 + H2
(Zinc and hydrochloric acid react to form
zinc chloride and hydrogen.)
Types of Chemical Reactions
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Double Displacement
AX + BY  AY + BX
CaCO3 + 2HCl  CaCl2 + H2CO3
Calcium carbonate and hydrochloric acid
yield calcium chloride and carbonic acid.
Types of Chemical Reactions
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Synthesis = Building
Decomposition = Breaking Down
Single Displacement = Metal Displaced
Double Displacement = Metals Swap Places
Types of Chemical Reactions
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Combustion
C2H5OH + 3O2  2CO2 + 3H2O
CH4 + 2O2  CO2 + 2H2O
2H2 + O2  2H2O
Fuel + Oxygen  release energy
Energy releasing reaction involving
oxygen and forming oxides of reactants.
Types of Chemical Reactions
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Acid – Base
a.k.a. neutralization
HCl + Mg(OH)2  MgCl2 + H2O
Acid + Base  Salt + Water
Acid = substance that releases H+ in solution
Base = substance that accepts H+ in solution
(usually by releasing OH-)
• HCl
NaOH
H2SO4
Mg(OH)2
Types of Chemical Reactions
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Synthesis = Building
Decomposition = Breaking Down
Single Displacement = Metal Displaced
Double Displacement = Metals Swap Places
Combustion = Burn Fuel, Release Energy
Acid-Base = Neutralization, Yield salt + water
Law of Conservation of Matter
• Matter, like energy, is neither created nor
destroyed in any process.
• “One may take it for granted that in every
reaction there is an equal quantity of
matter before and after.”
Lavoisier, 1768
“Balancing Equations”
• 2Ca + O2  2CaO
2
Ca
2
2
O
2