Chapter 13: Chemical Bonding

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Chapter 13 Chemical Bonding

• Section 1 Electrons and Chemical Bonding

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Identify the Elements and Tell Which Compounds
are Similar and Why

• C6H12O6
• C2H3O
• C6H8O6
• C6H8O7

Glucose (a sugar)
Ethanol (an alcohol)
Vitamin C (found in citrus fruits)
Citric Acid (found in lemons and other citrus
fruits)
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Atoms Combine Through Chemical Bonding

• How are the compounds on the previous page
  similar?
• The atoms of just 3 elements carbon, hydrogen,
  and oxygen combine in different patterns to
  form the substances sugar, alcohol, and citric
  acid.

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Chemical Bonding

• is the joining of atoms to form new substances.
• Once that chemical reaction happens, the new
  substances have different from those of the
  original elements.
• The force of attraction that holds the atoms
  together is called a chemical bond. This type of
  bond involves the electrons in the atom.

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Can we see these bonds?

• Unfortunately, no. They cannot be observed with
  your eyes. The way in which chemicals bond is a
  theory (unifying explanations for a broad range
  of observations and hypotheses.)
• Scientists use models to help explain this theory.

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Electron Number and Organization

• How do these atoms form chemical bonds?
• To figure that out, you have to know how many
  electrons are in a particular atom and how the
  electrons in the atom are organized.

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Electron Number and Organization
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Outer level electrons are key to bonding

• The example we just saw has 7 electrons in its
  outer shellthis is where most bonds form
• The electrons in the outermost level are called
  valence electrons
• So, how many valence electrons does a chlorine
  atom have?

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An Oxygen Molecule
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A Sodium Molecule
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Valence electrons and the Periodic Table

• The Periodic Table can work as a tool to help you
  identify the number of valence electrons in an
  atom.

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Valence Electrons and the Periodic Table
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Lets Review

• Determine the number of valence electrons in each
  of the following atoms
• lithium (Li)
• beryllium (Be)
• aluminum (Al)
• carbon (C)
• nitrogen (N)
• sulfur (S)
• bromine (Br)
• krypton (Kr)

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To Bond or Not to Bond

• Some atoms rarely bond at all!
• Atoms of the Noble Gases do not normally form
  chemical bonds because they (except helium) have
  8 valence electrons.
• Typically electrons that have 8 valance electrons
  do not form new chemical bonds.

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News Flash!

• The outermost energy level of an atom is
  considered to be full with 8 electrons!

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Remember

• Those numbers represent the maximum number of
  electrons the shell can hold.
• An atom that has fewer than 8 valance electrons
  is more reactive and more likely to form bonds by
  gaining, losing, or sharing electrons.

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Atoms Bond to Have a Filled Outermost Level
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Atoms Bond to Have a Filled Outermost Level
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A Full Set With Two?

• Not all atoms need 8 valance electrons for a
  filled outermost energy level.
• Heliums outermost level is filled at 2
• hydrogen and lithium form bonds with other atoms
  in order to have 2 electrons

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Lets Summarize

• What is the joining of atoms to form new
  substances called?

Chemical Bonding
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Lets Summarize

• Which electrons in an atom are likely to have
  more energy, those in levels close to the nucleus
  or those farther away?

Those farther away
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Lets Summarize

• Why do some atoms rarely bond?

They have a filled outermost energy level with 8
electrons, which makes them very nonreactive
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Section 2 Anticipation Guide True or False

• The type of chemical bond a compound has
  influences its melting and boiling point
• Some atoms share electrons
• Water, sugar, and carbon dioxide are compounds
  that have the same type of bonds
• The type of bonds formed in metals makes them
  very brittle and breakable.

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Section 2 Types of Chemical Bonds

• There are three types of bonds
• Ionic
• Covalent
• Metallic

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Ionic Bonds

• An ionic bond is the force of attraction between
  oppositely charged ions

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Lets review What is an ion?

• When the number of protons does not equal the
  number of electrons, the element becomes an ion.
• Positive charge Protons gt Electrons
• Negative charge Protons lt Electrons
• This usually happens when one of the valence
  electrons transfer from one atom to another

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Lets also recall

• that an atom is neutral because the number of
  protons is equal to the number of electrons so
  their charges cancel each other out.

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So, how exactly does an atom become an ion?

• First, the atom has to be close to another atom
  that either needs electrons or wants to give
  electrons away
• Once the atom gives away one or more electrons,
  it becomes a positive ion (more protons than
  electrons.)
• If it gains one or more protons, it becomes
  negative (more electrons that protons.)
• Either are ions

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Metal Atoms Lose Electrons

• Metal atoms have few electrons in their outermost
  shells so, when metal atoms form bonds with other
  elements, they tend to lose their outer electrons
  and become positive ions.
• Lets look at an example.

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Forming Positive IonsDo The Math!
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Forming Positive IonsDo The Math!
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Notice the change in how the positive ion is
written

• A sodium ion with a 1 charge (or has lost 1
  electron) is written as Na
• An aluminum atom that loses 3 electrons (3
  charge) is written Al3

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The Energy of Losing Electrons

• How does an atom lose electrons? Isnt there
  electromagnetic force holding them together?
• An atom can lose electrons and overcome the force
  holding them together easily if there are only 1
  or 2 electrons in the outermost shell

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OK, what about negative ions?

• In nonmetals, the outermost energy levels are
  almost full so nonmetals tend to gain electrons.
• Lets look at a couple of examples.

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Chlorine
Notice the- ide ending
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Oxygen
Notice the- ide ending
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The Energy of Gaining Electrons

• So an atom with 6 or 7 electrons require large
  amounts of energy for an electron to be taken
  away?
• Exactly! It is much easier for these elements to
  attract electrons to fill their shell. When they
  attract electrons, they give off energy rather
  than lose it.

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The Energy of Gaining Electrons

• For example, the Halogens (Group 17 elements)
  give off the most energy when they gain an
  electron

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Charged ions form a neutral compound

• Lets put sodium and chloride together

Neutral!
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Ions bond to form a crystal lattice

• When ions bond, they form a repeating
  three-dimensional pattern called a crystal
  lattice.
• They are formed by alternating positive and
  negative ions. This gives ionic compounds
  properties of high melting and boiling points,
  are brittle solids at room temp and break when
  hit with a hammer.

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Covalent Bonds

• Many materials that you find in your world every
  day like water, sugar and carbon dioxide are held
  together by bonds that do not involve ions.
• These type of bonds are called covalent bonds

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Covalent Bonds

• A covalent bond is the force of attraction
  between the nuclei of atoms and the electrons
  shared by the atoms. Covalent bonds make up
  molecules.
• Lets look at an example of 2 H atoms forming a
  covalent bond.

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Covalent Bonds
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Covalent Bonds

• How do covalent bonds work?
• In a hydrogen bond, the protons and the shared
  electrons attract one another. This attraction
  holds the atoms together. It also fills the
  outmost energy shell.
• Lets see it again.

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Covalent Bonds
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Covalently Bonded Atoms Make Up Molecules

• Unlike ionic bonds that form crystals, covalent
  compounds (bonds) consist of individual particles
  called molecules.
• A molecule is a neutral group of atoms held
  together by covalent bonds. Lets look at
  another example. A water molecule!

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Covalently Bonded Atoms Make Up Molecules
E-
E-
E-
8P 7N
E-
E-
E-
E-
E-
Notice the spaces on the outermost shell of the
oxygen atom. They want to be filled!
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So Do I Have to Draw the Whole Thing Out?

• NO! There is a shortcut!

You can use Electron Dot Diagrams. Lets see
how they work
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Making Electron Dot Diagrams

• These are also called . They only show the
  outer shell of the atom. Heres some examples.

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Making Electron Dot Diagrams

• Now lets put one together.

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Self-Check

• How many dots does the electron dot diagram of a
  sulfur atom have?

6. Check out the number above the group where
sulfur lives on the Periodic Table.
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Science Humor

• What is the one thing that atoms in molecules do
  not have to teach their children?

How to share with others!
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A molecule is the smallest part of a covalent bond

• Lets take water for example. If you divide
  water over and over again, you would end up with
  a single molecule of water.
• If that single molecule is divided, it becomes 2
  hydrogen atoms and 1 oxygen atom. It is no
  longer water.

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The Simplest Molecules

• All molecules are composed of at least two
  covalently bonded atoms.
• The simplest molecules are called diatomic
  molecules and consist of two atoms bonded
  together.
• Some elements are called diatomic elements
  because they are found in nature as diatomic
  molecules composed of two atoms of an element.

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The Simplest Molecules

• Hydrogen is a diatomic element
• Oxygen, nitrogen, and the halogens fluorine,
  chlorine, bromine, and iodine are also diatomic
• By sharing electrons, both atoms can fill their
  outer energy levels.

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More Complex Molecules

• Carbon atoms are the basis of many of the more
  complex molecules we are familiar with.
• Gasoline, plastic and even proteins ar examples
  of more complex molecules

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Metallic Bonds

• How is it that we can see and shape metal in so
  many different ways?
• Metal can be shaped because it contains a special
  bond called a metallic bond.

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Metallic Bonds

• A metallic bond is the force of attraction
  between a positively charged metal ion and the
  electrons in a metal.
• Remember, metal atoms tend to lose electrons and
  form positively charged ions.

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Electrons Move Throughout a Metal

• Metal atoms get so close to one another that
  their outermost energy levels overlap
• This allows their valance electrons available to
  move from the energy level of one atom to the
  energy level of another atom nearby.
• The ions are held together because metallic bonds
  extend throughout the metal in all directions.

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Metals Conduct Electric Current

• Metallic bonding is the reason why metals have
  particular propertiesespecially electrical
  conductivity

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Metals Can Be Reshaped

• Metallic bonds allow atoms in metals to be
  rearranged so they can be shaped (remember
  ductility and malleability?)

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How Metals Can Bend Without Breaking

• When a piece of metal is bent, some of the metal
  ions are forced closer together. The positive
  ions are still attracted to the electrons so the
  piece bends but doesnt break.

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Lets Check Understanding

• What happens to electrons in covalent bonding?

Electrons are shared between atoms
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Lets Check Understanding

• What type of element is most likely to form
  covalent bonds?

Nonmetals
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Lets Check Understanding

• What is a metallic bond?

The force of attraction between a positively
charged metal ion and the electrons in a metal
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Lets Check Understanding

• How does an atom develop a charge?

By gaining or losing electrons.
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Lets Check Understanding

• What properties are characteristic of ionic
  compounds?

They tend to have a high melting and boiling
point. At room temperature, they are brittle
solids and may break apart if hit with a hammer.
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Lets Check Understanding

• What is the smallest particle of a covalently
  bonded compound?

A molecule.
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Lets Check Understanding

• What properties of metals are due to the fact
  that metal ions can be rearranged?

Ductility and Malleability.