Chemical%20Bonding

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Chemical Bonding
Preview
Section 1 Electrons and Chemical
Bonding Section 2 Ionic Bonds Section 3
Covalent and Metallic Bonds
Concept Mapping
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Section 1 Electrons and Chemical Bonding
Bellringer
The following are some very common chemical
formulas. C6H12O6 C2H5OH C6H8O6 C6H8O7 Identif
y the elements in these compounds and predict
whether the compounds are similar to each other
and why. Record your answers in your science
journal.
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Section 1 Electrons and Chemical Bonding
Objectives

• Describe chemical bonding.
• Identify the number of valence electrons in an
  atom.
• Predict whether an atom is likely to form bonds.

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Section 1 Electrons and Chemical Bonding
Combining Atoms Through Chemical Bonding

• Chemical bonding is the joining of atoms to form
  new substances.
• An interaction that holds two atoms together is
  called a chemical bond. When chemical bonds form,
  electrons are shared, gained, or lost.

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Section 1 Electrons and Chemical Bonding
Combining Atoms Through Chemical Bonding,
continued

• Discussing Bonding Using Theories and Models We
  cannot see atoms and chemical bonds with the
  unaided eye.
• So, the use of models helps people discuss the
  theory of how and why atoms form bonds.

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Section 1 Electrons and Chemical Bonding
Electron Number and Organization

• The number of electrons in an atom can be
  determined from the atomic number of the element.
• Electrons in an atom are organized in energy
  levels.
• The next slide shows a model of the arrangement
  of electron in an atom. This model and models
  like it are useful for counting electrons, but do
  not show the true structure of an atom.

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Section 1 Electrons and Chemical Bonding
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Section 1 Electrons and Chemical Bonding
Electron Number and Organization, continued

• Outer-Level Electrons and Bonding Most atoms
  form bonds using only its valence electrons, the
  electrons in an atoms outermost energy level.

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Section 1 Electrons and Chemical Bonding
Electron Number and Organization, continued

• Valence Electrons and the Periodic Table You
  can use the periodic table to determine the
  number of valence electrons for atoms of some
  elements, as shown on the next slide.

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Section 1 Electrons and Chemical Bonding
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Section 1 Electrons and Chemical Bonding
To Bond or Not to Bond

• The number of electrons in the outermost energy
  level of an atom determine whether an atom will
  form bonds.
• Atoms that have 8 electrons in their outermost
  energy level do not usually form bonds. The
  outermost energy level is considered to be full
  if it contains 8 electrons.

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Section 1 Electrons and Chemical Bonding
To Bond or Not to Bond, continued

• Filling the Outermost Level An atom that has
  fewer than 8 valence electrons is more likely to
  form bonds than an atom that has 8 valence
  electrons is. Atoms bond by gaining, losing, or
  sharing electrons to have a filled outermost
  energy level.

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Section 1 Electrons and Chemical Bonding
To Bond or Not to Bond, continued

• Is Two Electrons a Full Set? Not all atoms need
  8 valence electrons to have a filled outermost
  energy level. Helium atoms need only 2 valence
  electrons because the outermost level is the
  first energy level.
• Atoms of hydrogen and lithium form bonds by
  gaining, losing, or sharing electrons to achieve
  2 electrons in the first energy level.

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Section 2 Ionic Bonds
Bellringer
Historically, salt has had many uses beyond just
a spice you put in your soup. Salts are
ionic compounds. Brainstorm some uses for salts,
things that contain salts, or words and phrases
containing the term salt. Where do you think salt
comes from? Write your answers in your science
journal.
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Section 2 Ionic Bonds
Objectives

• Explain how ionic bonds form.
• Describe how positive ions form.
• Describe how negative ions form.
• Explain why ionic compounds are neutral.

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Section 2 Ionic Bonds
Forming Ionic Bonds

• An ionic bond is a bond that forms when
  electrons are transferred from one atom to
  another atom.
• Charged Particles An atom is neutral because
  the number of electrons in an atom equals the
  number of protons. So, the charges cancel each
  other out.
• But when an atom gains or loses electrons, it
  becomes a charged particle called an ion.

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Section 2 Ionic Bonds
Forming Positive Ions

• Metal Atoms and the Loss of Electrons Atoms of
  most metals have few valence electrons and tend
  to lose these valence electrons and form positive
  ions.
• The Energy Needed to Lose Electrons Energy is
  needed to pull electrons away from atoms. The
  energy needed comes from the formation of
  negative ions.

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Section 2 Ionic Bonds
Forming Negative Ions

• Nonmetal Atoms Gain Electrons The outer energy
  level of nonmetal atoms is almost full. So,
  nonmetal atoms tend to gain electrons and become
  negative ions.
• The Energy of Gaining Electrons Energy is given
  off when nonmetals gain electrons. An ionic bond
  will form between a metal and a nonmetal if the
  nonmetal releases more energy than is needed to
  take electrons from the metal.

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Section 2 Ionic Bonds
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Section 2 Ionic Bonds
Ionic Compounds

• When ionic bonds form, the number of electrons
  lost by the metal atoms equals the number gained
  by the nonmetal atoms.
• The ions that bond are charged, but the compound
  formed is neutral because the charges of the ions
  cancel each other.

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Section 2 Ionic Bonds
Ionic Compounds, continued

• When ions bond, they form a repeating
  three-dimensional pattern called a crystal
  lattice, such as the one shown below.

• Properties of ionic compounds include
  brittleness, high melting points, high boiling
  points, and increase electrical conductivity when
  dissolved in water solutions.

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Section 3 Covalent and Metallic Bonds
Bellringer
Brainstorm a list of things made of metal.
Record your list in your science journal.
Describe three properties of metals based on your
list. The use of metal has been key to human
technological development. List the types of
metal that you use in your everyday life and how
you use them. What are the properties of metal
that make it useful? What are some of the
drawbacks of using metal?
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Section 3 Covalent and Metallic Bonds
Objectives

• Explain how covalent bonds form.
• Describe molecules.
• Explain how metallic bonds form.
• Describe the properties of metals.

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Section 3 Covalent and Metallic Bonds
Covalent Bonds

• A covalent bond forms when atoms share one or
  more pairs of electrons.
• Substances that have covalent bonds tend to have
  low melting and boiling points and are brittle in
  the solid state.
• Covalent bonds usually form between atoms of
  nonmetals, such as the atoms shown on the next
  slide.

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Section 3 Covalent and Metallic Bonds
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Section 3 Covalent and Metallic Bonds
Covalent Bonds, continued

• Covalent Bonds and Molecules Substances
  containing covalent bonds consist of particles
  called molecules. A molecule usually consists of
  two or more atoms joined in a definite ratio.
• The models on the next slide show two ways to
  represent the covalent bonds in a water molecule.

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Section 3 Covalent and Metallic Bonds
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Section 3 Covalent and Metallic Bonds
Covalent Bonds, continued

• One way to represent atoms and molecules is to
  use electron-dot diagrams. An electron-dot
  diagram shows only the valence electrons in an
  atom.

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Section 3 Covalent and Metallic Bonds
Covalent Compounds and Molecules

• A molecule is the smallest particle into which a
  covalently bonded compound can be divided and
  still be the same compound.
• The Simplest Molecules are made up of two bonded
  atoms. Molecules made up of two atoms of the same
  element are called diatomic molecules.

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Section 3 Covalent and Metallic Bonds
Covalent Compounds and Molecules, continued

• More-Complex Molecules Carbon atoms are the
  basis of many complex molecules.

• Each carbon atom can form four covalent bonds.
  These bonds can be with atoms of other elements
  or with other carbon atoms, as shown at right.

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Section 3 Covalent and Metallic Bonds
Metallic Bonds

• A metallic bond is a bond formed by the
  attraction between positively charged metal ions
  and the electrons in the metal.
• Movement of Electrons Throughout a Metal
  Bonding in metals is a result of the metal atoms
  being so close to one another that their
  outermost energy levels overlap. This overlapping
  allows valence electrons to move throughout the
  metal.

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Section 3 Covalent and Metallic Bonds
Metallic Bonding
Click below to watch the Visual Concept.
Visual Concept
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Section 3 Covalent and Metallic Bonds
Properties of Metals

• Conducting Electric Current Metallic bonding
  allows metals to conduct electric current.
• Electric current is conducted when valence
  electrons move within a metal. These electrons
  are free to move because the electrons are not
  connected to any one atom.

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Section 3 Covalent and Metallic Bonds
Properties of Metals, continued

• Reshaping Metals Because the electrons swim
  freely around the metal ions, atoms in metals can
  be rearranged. The properties of ductility and
  malleability describe a metals ability to be
  reshaped.
• Ductility is the ability to be draw in to wires.
• Malleability is the ability to be hammered into
  sheets.

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Section 3 Covalent and Metallic Bonds
Properties of Metals, continued

• Bending Without Breaking When a piece of metal
  is bent, some of the metal ions are forced closer
  together.
• But the metal does not break because the
  positive metal ions are always surround by and
  attracted to the electrons in the metal.

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Chemical Bonding
Concept Mapping
Use the terms below to complete the concept map
on the next slide. covalent bonds electrons ions
metallic bonds molecules chemical bonds
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Chemical Bonding
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Chemical Bonding