Chemical Bonding
Chemical Bonding
Do Now
Do Now
• Define
Define a compound.
a compound
• What is a compound made of?
• What are some examples of compounds?
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Compounds
• A
A compound is a pure substance made of compound is a pure substance made of
more than one kind of atom, and it can be broken down into its elemental components
broken down into its elemental components.
• Ex: CO2
• Ex: C
E C9H8O4
Chemical Bonds
Chemical Bonds
• Almost
Almost everything is made up of a everything is made up of a
combination of atoms that are held together by chemical bonds
by chemical bonds.
• Chemical Bond = an attraction between atoms that allows the formation of chemical
that allows the formation of chemical substances that contain two or more atoms
• The bond results from simultaneous attraction Th b d
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of electrons to 2 nuclei
Why do atoms bond?
Why do atoms bond?
• As individual atoms, many atoms are considered unstable (if they do not have 8 valence electrons).
unstable (if they do not have 8 valence electrons).
• To achieve 8 valence electrons, atoms bond with each other in a variety of ways.
• Bonded atoms acquire 8 valence electrons and B d d
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therefore become more stable.
• As a result of bond formation, both atoms achieve a ,
valence shell that is identical to one of the noble gases. • 8 valence electrons is associated with maximum stability It is known as a stable octet
stability. It is known as a stable octet.
• Remember: Most atoms also want to have 8 valence electrons!
Energy changes
Energy changes
• Transferring electrons involves energy change.
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g
• Energy based on position is called potential energy. • Chemical Energy = the particular form of potential energy involved in the making and breaking of chemical bonds
breaking of chemical bonds
• Remember: Forming a chemical bond causes a g
chemical change, because a new substance is produced with new properties.
How do bonds change energy?
How do bonds change energy?
• As individual atoms, many atoms have a very high s d dua ato s, a y ato s a e a e y g
potential energy and are considered unstable (if they do not have 8 valence electrons).
• Bonded atoms acquire 8 valence electrons and therefore become more stable, their energy decreases.
• 8 valence electrons is associated with maximum stability and minimum potential energy content
stability and minimum potential energy content.
• Potential energy decrease occurs when atoms form chemical bonds with one another
form chemical bonds with one another.
Energy changes
Energy changes
• Remember: Ionization energy = the energy required to remove an electron from an atom
• Ex: Na + energy Æ Na+ + e‐
• Remember: Electron affinity = the energy needed to add an electron onto a neutral atom
• Ex: Cl + e‐ Æ Cl‐ + energy
• The
The energy released is less than the energy required to energy released is less than the energy required to
remove an electron, but there is also energy released by forming the salt, so overall, energy is released!
Review
• Chemical reaction: Chemical reaction:
– Reactants → Products
• Exothermic Reaction = energy release
– Reactants Æ Products + energy
• Endothermic Reaction = energy absorbed
– Reactants + energy Æ
Reactants + energy Æ Products
Energy Changes and Stability in Bonding an Exothermic Process
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•
•
•
•
When chemical bonds are formed energy is released (an formed, energy is released
(an
exothermic process). The products are more stable than the reactants.
Whenever large amounts of energy are released in the formation of a bond, the bond g
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is said to be strong and very stable.
Weak bonds and unstable systems are associated with the release of small amounts
the release of small amounts of energy.
The potential energy of the products is lower than the potential energy of the
potential energy of the reactants.
Energy Changes and Stability in Bonding in an Endothermic Process
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• When chemical bonds e c e ca bo ds
are broken, energy is absorbed (an endothermic process). d h
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• The reactants are more
stable than the products.
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• The potential energy of the products is higher
the products is higher
than the potential gy
energy of the reactants.
Practice
Ex: Which statement best describes the production Ex:
Which statement best describes the production
of a chlorine molecule according to the reaction Cl + Cl → Cl2 + 58 Kcal?
Cl + Cl →
+ 58 Kcal?
a. A bond is broken, and the reaction is exothermic. b A bond is broken and the reaction is endothermic
b. A bond is broken, and the reaction is endothermic.
c. A bond is formed, and the reaction is exothermic.
d A bond is formed and the reaction is endothermic
d. A bond is formed, and the reaction is endothermic.
Which of the bonds is most stable?
Which of the bonds is most stable?
• The
The greater the energy released during bond greater the energy released during bond
formation the more stable the bond.
Bond
Energy released in
Formation (kcal/mol)
H F
H-F
135
H-Cl
103
H B
H-Br
87
H-I
71
Review
• Is energy released or absorbed when a bond is formed?
• Is energy released or absorbed when a bond is broken?
• Which is the endothermic potential energy diagram?
• Which is the exothermic potential energy diagram? Which is the exothermic potential energy diagram?
A B
INTRAMOLECULAR BONDS
INTRAMOLECULAR BONDS
• Bonds within the compound, hold atoms together.
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• TYPES OF INTRAMOLECULAR BONDS
– 1. IONIC BONDS
– 2. COVALENT BONDS
• When atoms bond, valence electrons are redistributed. The way they are redistributed determines the type of
The way they are redistributed determines the type of bond.
IONIC BONDING
IONIC BONDING
COVALENT BONDING
COVALENT BONDING
Reactivity Review
Reactivity Review
• Remember: most atoms are satisfied when there outer energy level is complete with 8 valence electrons = octet rule. Noble gases are the least reactive elements, because
• Noble gases are the least reactive elements, because they have completely filled outer energy levels.
• Alkali metals (group 1) and halogens (group 17) are the most reactive elements because they will react to lose
most reactive elements, because they will react to lose or gain electrons so the outer orbital is full. – Alkali metals (group 1) have 1 electron in their outer energy level so they can easily give up that 1 electron
energy level, so they can easily give up that 1 electron.
– Halogens (group 17) have 7 electrons in their outer energy level, so they can easily gain 1 electron.
CATION
(ca+ion)
ANION
(aNion)
Some stable ions
Some stable ions
Some stable ions without noble gas configuration
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Atoms vs. Ions
Atoms vs. Ions
• Ions
Ions and their parent atoms have very and their parent atoms have very
different properties.
– Ex: Sodium and chlorine atoms are very reactive, Ex: Sodium and chlorine atoms are very reactive
producing a violent reaction when brought together. However, after the reaction is complete, g
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,
a stable, less reactive solid (sodium chloride) remains (made of sodium ions and chlorine ions).
Metals vs Nonmetals
Metals vs Nonmetals
• Most metals form cations, because it requires ,
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less energy to lose a few electrons compared to gaining a lot of electrons.
• Most nonmetals form anions, because it requires Most nonmetals form anions because it requires
less energy to gain a few electrons compared to losing a lot of electrons.
• Remember: Ionization energy = the energy required to remove an electron from an atom
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– PERIOD TREND: Tends to increase across a period
– GROUP TREND: Tends to decrease down a group GROUP TREND: Tends to decrease down a group