Ionic and Metallic Bonding Chapter 7

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Ionic and Metallic BondingChapter 7

• Honors Chemistry
• 2007-2008

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7.1 Ions

• Chemical bond is a mutual electrical attraction
  between the nuclei and valence electrons of
  different atoms that binds the atoms together..

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Valence Electrons

• Valence Electrons are the electrons in the
  highest occupied energy level of an elements
  atoms. The number of valence electrons largely
  determines the chemical properties of an element.
• To find the number of valence electrons
  in an atom of a representative element, simply
  look at its group number.
• Example elements of Group 1A (hydrogen,
  lithium, sodium, potassium, and so forth) all
  have one valence electron, corresponding to
  the 1 in the 1A.
• Carbon and silicon, in Group 4A, have four
  valence electrons.
• Valence electrons are usually the only
  electrons used in chemical bonds..

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Valence Electrons

• Electron Dot Structures are diagrams that show
  valence electrons as dots.

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Valence Electrons

• Octet Rule
• As learned in Chapter 6, noble gases are
  unreactive in chemical reactions.
• Valence shell electrons are s and p orbital
  electrons.
• Chemical compounds tend to form so that each
  atom, by gaining, losing, or sharing electrons,
  has an octet of electrons in its highest occupied
  energy level (valence shell).
• Atoms of the metal elements tend to lose their
  valence electrons, leaving a complete octet in
  the next-lowest energy level.
• Atoms of nonmetals elements tend to gain
  electrons or to share electrons with another
  nonmetal element to achieve a complete octet..

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Formation of Cations

• An atom is electrically neutral because it has an
  equal number of protons and electrons an ion
  forms when an atom or group of atoms loses or
  gains electrons.
• An atoms loss of valence electrons produces a
  cation, or a positively charged ion.
• For metallic elements, the name of a cation is
  the same as the name of the element..

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Formation of Cations

• Example A sodium atom (Na) becomes the sodium
  cation
• (Na or Na1)
• The sodium atom has an electron configuration
  that is identical to the noble gas neon.
• In forming an ion the sodium atom loses one
  valence electron and is left with an octet
  (eight electrons) in its highest energy level.
• Because the number of protons in the sodium
  nucleus is still eleven, the loss of one unit of
  negative charge (an electron) produces a cation
  with a charge of 1 (or 1)..

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Formation of Cations

• Example A sodium atom (Na) becomes the sodium
  cation
• (Na or Na1)
• Both sodium and neon atoms have eight electrons
  in their valence shells.

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Formation of Cations

• Example A sodium atom (Na) becomes the sodium
  cation
• (Na or Na1)

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Formation of Cations

• Transition metals the charges of cations may
  vary.
• Some ions formed by transition metals do not have
  noble-gas configurations and are therefore
  exceptions to the octet rule.

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Formation of Anions

• An anion is an atom or a group of atoms with a
  negative charge.
• The gain of negatively charged electrons by a
  neutral atom produces an anion.
• The name of the anion typically ends in the
  suffix -ide.
• Example The chlorine atom (Cl) forms a chloride
  ion (Cl or Cl 1)
• Cl ? Cl 1

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Formation of Anions

• Example The chlorine atom (Cl) forms a chloride
  ion (Cl1? or Cl 1)
• Cl ? Cl 1

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Formation of Anions

• Example The oxygen atom (O) forms a oxide ion (O
  2)
• O ? O 2

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Common Ions

• Common Ions
• Refer to the common ion sheet..

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7.2 Ionic Bonds and Ionic Compounds

• Compounds composed of cations and anions are
  called ionic compounds.
• Ionic compounds are usually composed of metal
  cations and nonmetal anions (or polyatomic ions)
• Although they are composed of ions, ionic
  compounds are electrically neutral.
• Total positive charge of the cations equals the
  total negative charge of the anions..

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Ionic Bonds

• Anions and cations have opposite charges and
  attract one another by means of electrostatic
  forces.
• The electrostatic forces that hold ions together
  in ionic compounds are called ionic bonds..

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Ionic Bonds

• Example consider the reaction between a sodium
  atom and a chlorine atom.
• Sodium has a single valence electron that it can
  easily lose.
• Chlorine has 7 valence electrons and can easily
  gain one electron.
• When sodium reacts with chlorine
• The sodium atom gives its one valence electron
  to a chlorine atom.
• The ratio of sodium to chlorine is 11 and both
  ions have a stable octet..

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Ionic Bonds

• Example consider the reaction between a sodium
  atom and a chlorine atom.

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Ionic Bonds

• Example consider the reaction between a sodium
  atom and a chlorine atom.

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Ionic Bonds

• Example consider the reaction between a sodium
  atom and a chlorine atom.

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Formula Unit

• Ionic compound sodium chloride is composed of
  equal numbers of sodium cations (Na) and
  chloride anions (Cl-).
• The ions in solid sodium chloride are arranged in
  an orderly pattern.
• There are no single discrete units, only a
  continuous array of ions. (See fig 7.8, pg
  195)
• Chemical Formula shows the kinds and numbers of
  atoms in the smallest representative unit of a
  substance.
• NaCl is the chemical formula for sodium
  chloride.
• A formula unit is the lowest whole-numbered ratio
  of ions in an ionic compound.
• NaCl is also the formula unit for sodium
  chloride..

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Formula Unit

• Ionic compound sodium chloride is composed of
  equal numbers of sodium cations (Na) and
  chloride anions (Cl-).

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Properties of Ionic Compounds

• Most ionic compounds are solids at room
  temperature.
• The arrangement of repeating three-dimensional
  patterns leads to large attractive forces within
  the solid.
• Ionic compounds generally have high melting
  points.
• Sodium chloride melts at 804 o C..

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Properties of Ionic Compounds

• Coordination number of an ion is the number of
  ions of opposite charge that surround the ion in
  the crystal.
• Each sodium ion has 6 chloride ions around it.
• Each chloride ion has 6 sodium ions around it.
• Thus the coordination number for both is 6..

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Properties of Ionic Compounds

• Components ions in crystals are arranged in
  repeating three-dimensional patters. These give
  rise to the beauty of these crystals.

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Properties of Ionic Compounds

• Most ionic compounds will not conduct electricity
  in solid state.
• Most will conduct electricity when melted or
  dissolved in water. (Fig 7.11, pg 198)

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7.3 Bonding in Metals

• The valence electrons of metal atoms can be
  modeled as a sea of electrons.
• That is, the valence electrons are mobile and can
  drift freely from one metal atom to another
  metal atom.
• Metallic bonds consist of the attraction of the
  loosely bound electrons to the metal atoms.
• This sea of electrons model explains many
  physical properties of metals..

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7.3 Bonding in Metals

• Metal are good conductors of electrical current.

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7.3 Bonding in Metals

• Metals are ductile - they can be drawn into
  wires.

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7.3 Bonding in Metals

• Metals are malleable - they can be hammered or
  forced into shapes, where as ionic compounds are
  brittle.

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7.3 Bonding in Metals

• Metals are malleable - they can be hammered or
  forced into shapes, where as ionic compounds are
  brittle.

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7.3 Bonding in Metals

• Metals are malleable - they can be hammered or
  forced into shapes, where as ionic compounds are
  brittle.

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Crystalline Structure of Metals

• Fruit in the grocery store are staked in what we
  call close- packed arrangement. This arrangement
  helps save space while allowing as many oranges
  to be staked as possible.
• Metals that contain only one kind of atom are
  among the simplest forms of all crystalline
  solids.
• Metal atoms are arranged in very compact and
  orderly patterns.
• For sphere of identical size, there several
  closely packed arrangements possible..

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Crystalline Structure of Metals

• Body-centered cubic every atom has eight
  neighbors (except those on the surface).

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Crystalline Structure of Metals

• Face-centered cubic every atom has twelve
  neighbors.

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Crystalline Structure of Metals

• Hexagonal close-packed arrangement every atom
  also has twelve neighbors. Because of the
  hexagonal shape, the pattern is different form
  the face-centered cubic arrangement.

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Alloys

• Alloys are mixtures composed to two or more
  elements, at least one of which is a metal.
• Brass is an alloy of copper and zinc.
• Alloys are important because their properties are
  often superior to those of their component
  elements.
• Sterling silver (92.5 silver 7.5 copper) is
  harder and more durable than pure silver, but
  still soft enough to be made into jewelry and
  table ware..

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Alloys

• Most important alloys are steels.
• Principal elements in addition to iron and carbon
  are boron, chromium, manganese, molybdenum,
  nickle, tungsten, and vanadium.
• Properties include corrosion resistance,
  ductility, hardness, and toughness..

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Alloys

• Alloys can form from their component atoms in
  different ways.
• Atoms of the components in an alloy are about the
  same size, they can replace each other in the
  crystal.
• This type of alloy is called a substitutional
  alloy.
• If the atomic sizes are quite different, the
  smaller atoms can fit into the interstices
  (spaces) between the larger atoms.
• Such an alloy is called an interstitial alloy.