Chapter 7 Ionic and Metallic Bonding

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Chapter 7Ionic and Metallic Bonding
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valence Electrons
Scientists learned that all of the elements
within each group of the periodic table behave
similarly because they have the same number of
valence electrons. valence electrons are the
electrons in the highest occupied energy level of
an elements atom. 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
elements, simply look at its group
number Elements of Group IA have one valence
electron. Elements in Group 4A have four valence
electrons, and so forth
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valence Electrons
The noble gases, Group 8A, are the only
exceptions to the group-number rule. Helium has
two valence electrons, and all of the other noble
gases have eight. valence electrons are
usually the only electrons used in chemical
bonds. As a general rule, only the valence
electrons are shown in electron dot
structures. Electron dot structures are diagrams
that show valence electrons as dots.
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Electron Dot Structures
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The Octet Rule
Noble gases, such as neon and argon, are
unreactive in chemical reactions. (They are
stable) Gilbert Lewis explained why atoms form
certain kinds of ions and molecules in the octet
rule The Octet Rule - in forming compounds,
atoms tend to achieve the electron configuration
of a noble gas. An octet is a set of eight. (each
noble gas except helium has eight electrons in
its highest energy level) Atoms of the metallic
elements tend to lose their valence electrons,
leaving a complete octet in the next-lowest
energy level. Atoms of some nonmetallic elements
tend to gain electron or to share electrons with
another nonmetallic element to achieve a complete
octet.
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Formation of Cations
An atom is electrically neutral because it has
equal numbers of protons and electrons an ion
forms when an atoms or group of atoms loses or
gains electrons. An atoms loss of valence
electrons produced a cation, or a positively
charged ion. For metallic elements, the name
of the ion is the same as the name of the
element. Although their names are the same,
there are many important chemical differences
between metals and their cations.
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Formation of Cations
An atom is electrically neutral because it has
equal numbers of protons and electrons an ion
forms when an atoms or group of atoms loses or
gains electrons. An atoms loss of valence
electrons produced a cation, or a positively
charged ion. For metallic elements, the name
of the ion is the same as the name of the
element. Although their names are the same,
there are many important chemical differences
between metals and their cations.
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Formation of Cations
Using electron dot structures, you can show the
ionization of some elements more simply. Na
Na e-
Sodium atom Sodium ion
electron neutral
1 unit of charge 1 unit of - charge Mg
Mg2 2e-
Magnesium atom Magnesium ion
electron neutral
2 unit of charge 2 units of - charge
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Transition Metals
For transition metals, the charges of cations may
vary. An atom of iron (Fe) may lose two, or
three electrons forming either Fe2 or Fe3 ions.
Some ions formed by transition metals do not
have noble gas electron configurations and are
therefore exceptions to the octet rule. Ag is an
example - 1s22s22p63s23p63d104s24p64d105s1 To
achieve the structure of krypton, which is the
preceding noble gas, a silver atom would have to
lose eleven electrons.
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Transition Metals
Ions with charges of three or greater are
uncommon, and losing eleven electrons is highly
unlikely. If Ag loses its 5s1 electron, the
configuration that results, (4s24p64d10) with 18
electrons in the outer energy level and all of
the orbitals filled, is relatively favorable in
compounds. Such a configuration is known as
pseudo noble-gas electron configuration. Ag
forms a positive ion (Ag) in this way.
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Formation of Anions
The gain of negatively charge electrons by a
neutral atom produces an anion. The name of an
anion of a nonmetallic element is not the same as
the element name. The name of the ion typically
ends in -ide. Chlorine atom (Cl) forms a
chloride ion (Cl-) Oxygen atom (O) forms an oxide
ion (O2-) Because they have relatively full
valence shells, atoms of nonmetallic elements
attain noble-gas electron configurations more
easily by gaining electrons than by losing them.
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Formation of Anions
Chlorine belongs to Group 7A and has seven
valence electrons. A gain of one electron gives
chlorine an octet and converts a chlorine atom
into a chloride ion. Atoms of nonmetallic
elements form anions by gaining enough valence
electrons so as to attain the electron
configuration of the nearest noble gas. The
chloride ion has the same electron configuration
as the noble gas argon. Chloride ion (Cl-)
1s22s22p63s23p6 Argon (Ar) 1s22s22p63s23p6
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Food For Thought
Chlorine atoms need one more valence electron to
achieve the electron configuration of the nearest
noble gas. Any electron in an atom outside the
noble gas core is called a valence electron.
Various atoms of the representative elements
form ions and gain a noble-gas electron
configuration
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Formation of Anions
Halide ions the ions that are produced when
atom of chlorine and other halogens gain
electrons All halogen atoms have seven valence
electrons and need to gain only one electron to
achieve the electron configuration of a noble
gas. All halide ions (F-, Cl-, Br-, and I-)
have charge of 1-.
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Questions
How can you determine the number of valence
electrons in an atom of a representative element?
Look up the group number of that element
Atoms of which elements tend to gain electrons?
Atoms of which elements tend to lose
electrons? Nonmetallic gain
metallic - lose How do cations form? How do
anions form? Cation atom loses valence
electrons Anion atom
gains valence electrons
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End of Section 7.1
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Formation of Ionic Compounds
Compounds composed of cations and anions are
called ionic compounds. Ionic compounds are
usually composed of metal cations and nonmetal
anions. Ex NaCl is formed from Na
Cl- Although they are composed of ions, ionic
compounds are electrically neutral. The total
charge of the cations equals the total charge
of the anions. 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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Formation of Ionic Compounds
Compounds composed of cations and anions are
called ionic compounds. Ionic compounds are
usually composed of metal cations and nonmetal
anions. Ex NaCl is formed from Na
Cl- Although they are composed of ions, ionic
compounds are electrically neutral. The total
charge of the cations equals the total charge
of the anions. 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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Formation of Ionic Compounds
Look at the reaction of a Na atom and a chlorine
atom. Na has 1 valence electron that it can
easily lose. (Na is in group 1A of the
representative elements, thus has 1 valence
electron) Cl has seven valence electrons and can
easily gain one electron. (Cl is in group 7A of
the representative elements, thus has 7 valence
electrons) If Na loses its valence electron it
achieves the stable electron configuration of
neon. If Cl gains a valence electron, it achieves
the stable electron configuration of argon.
(Remember the Octet Rule)
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Formation of Ionic Compounds
When Na and Cl react, the Na atom gives its one
valence electron to a Cl atom. They react in a
11 ratio and both ions have stable octets.

Na
Cl- 1s22s22p6 1s22s22p63s23p6
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Formula Units

• Chemists represent the composition of substances
  by writing chemical formulas. A 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-number ratio
  of ions in an ionic compound. One Na to each
  Cl-, thus the formula unit for sodium chloride is
  NaCl.
• Even though ionic charges are used to derive the
  correct formulas, they are not shown when you
  write the formula unit of the compound

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Formula Units

• The ionic compound Magnesium chloride (MgCl2)
  contains magnesium cations (Mg2) and chloride
  anions (Cl-)
• In MgCl2, the ratios of Mg2 to Cl- is 12 (One
  Mg2 to two Cl-). Its formula unit is MgCl2
• Because there are twice as many Cl- (each with a
  1- charge) as Mg2 (each with a 2 charge), the
  compound is electrically neutral.
• Another example Al3 Br- combine to form
  AlBr3.

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Questions

• Use electron dot structures to determine formulas
  of the ionic compounds formed when
• Potassium reacts with iodine
• KI
• Aluminum reacts with oxygen
• Al2O3

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Properties of Ionic Compounds

• Most ionic compounds are crystalline solids at
  room temperature.
• The component ions in such crystals are arranged
  in repeating three-dimensional patterns.
• In NaCl, each sodium ion is surrounded by six
  chloride ions, and each chloride ion is
  surrounded by six sodium ions.
• In this arrangement, each ion is attracted
  strongly to each of its neighbors and repulsions
  are minimized.
• The large attractive forces result in a very
  stable structure.

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Properties of Ionic Compounds

• Ionic compounds can conduct an electric current
  when melted or dissolved in water.
• When NaCl is melted, the orderly crystal
  structure breaks down.
• The movement of the ions allows electricity to
  flow

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Questions

• How can you describe the electrical charge of an
  ionic compound?
• Electrically neutral
• What properties characterize ionic compounds?
• Usually solids at room temperature have high
  melting points conduct electric current when
  melted or dissolved in water.
• Define an ionic bond
• Electrostatic forces that hold ions together in
  an ionic compound

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Questions

• Write the correct chemical formula for the
  compounds formed from each pair of ions.
• K , S2- Ca2 , O2-
• Na , O2- Al3 , N3-
• K2S , CaO, Na2O , AlN
• Write formulas for each compound barium
  chloride, magnesium oxide, lithium oxide, calcium
  fluoride
• BaCl2 MgO Li2O CaF2
• Which pairs of elements are likely for form ionic
  compounds?
• Cl, Br Li, Cl K, He I, Na
• Li, Cl I, Na

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End of Section 7.2
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Metallic Bonds Properties

• Metals are made up of closely packed cations
  rather than neutral atoms.
• The valence electrons of metal atoms can be
  modeled as a sea of electrons. (they are mobile
  and can drift freely from one part of the metal
  to another).
• Metallic bonds consists of the attraction of the
  free-floating valence electrons from the
  positively charged metal ion.
• The sea-of-electrons model explains many physical
  properties of metals.
• Good conductors of electrical current because
  electrons can flow freely.
• Ductile they can be drawn into wires.
• Malleable they can be hammered or forced into
  shapes.

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Crystalline Structure of Metals

• The crystalline structures of metals
• can be compared to the stacking of
• oranges in the grocery store to save
• space.
• Metals are crystalline and they are
• arranged in very compact and orderly
• patterns.

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Crystalline Structure of Metals

• There are several closely packed arrangements
  that are possible.
• body-centered cubic arrangement
• face-centered cubic arrangement
• hexagonal close-packed arrangement
• Body-centered cubic
• Every atom (except those on the
• Surface) has eight neighbors.

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Crystalline Structure of Metals

• Face-centered cubic arrangement
• every atom has twelve neighbors.

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Crystalline Structure of Metals

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

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Alloys
Very few of the metallic items that you use every
day are pure metals. Ex spoons. Most of the
metals you encounter are alloys. Alloys are
mixtures composed of two or more elements., at
least on of which is a metal. Ex Brass (Cu
Zn) Alloys 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 tableware.
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Alloys
Bronze 7 parts copper to 1 part tin. Bronze is
harder than copper and more easily cast.
Nonferrous (non-iron) alloys are commonly used
to make coins. The most important alloys today
are steels. Alloys can form from their component
atoms in different ways. If the atoms of the
components in an alloy are about the same size,
they can replace each other n the crystal.
(substantial alloy) If the atomic sizes are
different, the smaller atoms can fit into the
spaces between the larger atoms. (interstitial
alloy)
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Questions
How do chemists model the valence electrons in
metal atoms? Metal cations surrounded by a sea
of mobile valence electrons. How can you
describe the arrangement of atoms in
metals? Atoms in metals are arranged in a compact
and orderly manner Why are alloys more useful
than pure metals? Their properties are often
superior to their component elements.
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End of Chapter 7