The submicroscopic structure of ionic compounds helps explain why they share certain macroscopic pro

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Types of Compounds Basic Concepts
Topic 7
Ionic Compounds

• The submicroscopic structure of ionic compounds
  helps explain why they share certain macroscopic
  properties such as high melting points,
  brittleness, and the ability to conduct
  electricity when molten or when dissolved in
  water.

• You have learned that ionic compounds are made up
  of oppositely charged ions held together strongly
  in well-organized units.

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Ionic Compounds

• Because of their structure, they usually are hard
  solids at room temperature and are difficult to
  melt. Look at the structure of magnesium oxide.

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Ionic Compounds

• When ionic compounds melt or dissolve in water,
  their three-dimensional structure breaks apart,
  and the ions are released from the structure.

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Ionic Compounds

• These charged ions are now free to move and can
  conduct an electrical current.

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Binary Ionic Compounds

• Formulas are part of the language that is used to
  communicate information about substances.

• As a first step in studying this new language,
  you will learn how to name and write formulas for
  ionic compounds.

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Binary Ionic Compounds

• Sodium chloride (NaCl) contains only sodium and
  chlorine, and potassium iodide (KI) contains only
  potassium and iodine.

• Each is an example of a binary compound, which is
  a compound that contains only two elements.

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Binary Ionic Compounds

• Binary ionic compounds can contain more than one
  ion of each element, as in CaF2, but they are not
  composed of three or more different elements, as
  are more complex compounds.

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Binary Ionic Compounds

• To name a binary ionic compound, first write the
  name of the positively charged ion, usually a
  metal, and then add the name of the nonmetal or
  negatively charged ion, whose name has been
  modified to end in -ide.

• The compound formed from potassium and chlorine
  is called potassium chloride.

• Magnesium combines with oxygen to form a compound
  called magnesium oxide.

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Binary Ionic Compounds

• You are already familiar with one formula for an
  ionic compoundNaCl.

• Sodium chloride contains sodium ions that have a
  1 charge and chloride ions that have a 1
  charge.

• You have learned that compounds are electrically
  neutral.

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Binary Ionic Compounds

• This means that the sum of the charges in an
  ionic compound must always equal zero.

• Thus, one Na balances one Cl in sodium
  chloride.

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Binary Ionic Compounds

• When you write a formula, you add subscripts to
  the symbols for the ions until the algebraic sum
  of the ions charges is zero.

• The smallest subscript to both ions that results
  in a total charge of zero is 1.

• However, no subscript needs to be written because
  it is understood that only one ion or atom of an
  element is present if there is no subscript.

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Binary Ionic Compounds

• The formula NaCl indicates that sodium chloride
  contains sodium and chloride ions, that there is
  one sodium ion present for every chloride ion in
  the compound, and that the compound has no
  overall charge.

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Binary Ionic Compounds

• If more than one ion of a given element is
  present in a compound, the subscript indicates
  how many ions are present.

• The mineral known as fluorite is calcium
  fluoride, which has the formula CaF2.

• This formula indicates that there is one calcium
  ion for every two fluoride ions in the compound.

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Binary Ionic Compounds

• In an ionic compound, a formula represents the
  smallest ratio of atoms or ions in the compound.

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Binary Ionic Compounds

• In a covalent compound, the smallest unit of the
  compound is a molecule, so a formula represents a
  single molecule of a compound.

• This simplest ratio of ions in a compound is
  called a formula unit.

• Each formula unit of calcium fluoride consists of
  one calcium ion and two fluoride ions.

• Each of the three ions has a stable octet
  configuration of electrons, and the formula unit
  has no overall charge.

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Predicting Charge on Ions

• The noble gases each have eight electrons in
  their outer-energy levels.

• Metals have few outer-level electrons so they
  tend to lose them and become positive ions.

• Sodium must lose just one electron, becoming an
  Na ion.

• Calcium must lose two electrons, becoming a Ca2
  ion.

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Predicting Charge on Ions

• Most nonmetals, on the other hand, have
  outer-energy levels that contain four to seven
  electrons, so they tend to gain electrons and
  become negative ions.

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Predicting Charge on Ions

• Because all elements in a given group have the
  same number of electrons in their outer-energy
  level, they must lose or gain the same number of
  electrons to achieve a noble-gas electron
  configuration.

• Metals always lose electrons and nonmetals always
  gain electrons when they form ions.

• The charge on the ion is known as the oxidation
  number of the atom.

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Predicting Charge on Ions

• The oxidation numbers for many elements in the
  main groups are arranged by group number.

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Predicting Charge on Ions

• Oxidation numbers for elements in Groups 3
  through 12, the transition elements, cannot be
  predicted by group number.

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Predicting Charge on Ions

• Aluminum is in Group 13, so it loses its three
  outer electrons to become an Al3 ion oxygen is
  in Group 16 and has six valence electrons, so it
  gains two electrons to become an O2 ion.

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Predicting Charge on Ions

• Notice that one of aluminums three electrons has
  not been taken up by the oxygen atom.

• Because all the electrons must be accounted for,
  more than one oxygen atom must be involved in the
  reaction.

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Predicting Charge on Ions

• But, oxygen cannot gain only one electron, so a
  second aluminum atom must be present to
  contribute a second electron to oxygen.

• In all, two Al3 ions must combine with three O2
  ions to form Al2O3.

• Remember that the charges in the formula for
  aluminum oxide must add up to zero.

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Types of Compounds Basic Concepts
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Compounds Containing Polyatomic Ions

• The ions you have studied thus far have contained
  only one element.

• However, some ions contain more than one element.

• An ion that has two or more different elements is
  called a polyatomic ion.

• Although the individual atoms have no charge, the
  group as a whole has an overall charge.

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Compounds Containing Polyatomic Ions
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Types of Compounds Basic Concepts
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Compounds Containing Polyatomic Ions
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Types of Compounds Basic Concepts
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Compounds Containing Polyatomic Ions

• Ionic compounds may contain positive metal ions
  bonded to negative polyatomic ions, such as in
  NaOH negative nonmetal ions bonded to positive
  polyatomic ions, such as in NH4I or positive
  polyatomic ions bonded to negative polyatomic
  ions, such as in NH4NO3.

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Compounds Containing Polyatomic Ions

• To write the formula for an ionic compound
  containing one or more polyatomic ions, simply
  treat the polyatomic ion as if it were a
  single-element ion by keeping it together as a
  unit.

• Remember that the sum of the positive and
  negative charges must equal zero.

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Compounds Containing Polyatomic Ions

• Multiples of a polyatomic ion in a formula can be
  indicated by placing the entire polyatomic ion,
  without the charge, in parentheses.

• Write a subscript outside the parentheses to show
  the number of polyatomic ions in the compound.

• Never change the subscripts within the polyatomic
  ion.

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Compounds Containing Polyatomic Ions

• To do so would change the composition of the ion.

• The formula for the compound that contains one
  magnesium ion and two nitrate ions is Mg(NO3)2.

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Compounds Containing Polyatomic Ions

• To name a compound containing a polyatomic ion,
  follow the same rules as used in naming binary
  compounds.

• Name the positive ion first, followed by the
  negative ion.

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Compounds Containing Polyatomic Ions

• However, do not change the ending of the negative
  polyatomic ion name.

• The name of the compound composed of calcium and
  the carbonate ion is calcium carbonate.

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Compounds Containing Polyatomic Ions

• Calcium is in Group 2, so its ion has a 2
  charge. The carbonate ion has a 2 charge.

• To form a neutral compound, one Ca2 ion must
  combine with one CO32 ion to give the formula
  CaCO3.

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Compounds of Transition Elements

• Elements known as transition elements are located
  in Groups 3 through 12 in the periodic table.

• Transition elements form positive ions just as
  other metals do, but most transition elements can
  form more than one type of positive ion.

• In other words, transition elements can have more
  than one oxidation number.

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Compounds of Transition Elements

• For example, copper can form both Cu and Cu2
  ions, and iron can form both Fe2 and Fe3 ions.

• Zinc and silver are two exceptions to the
  variability of other transition elements each
  forms one type of ion.

• The zinc ion is Zn2 and the silver ion is Ag.

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Compounds of Transition Elements

• Chemists must have a way to distinguish the names
  of compounds formed from the different ions of a
  transition element.

• They do this by using a Roman numeral to indicate
  the oxidation number of a transition element ion.

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Types of Compounds Basic Concepts
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Compounds of Transition Elements

• This Roman numeral is placed in parentheses after
  the name of the element.

• No additional naming system is needed for zinc
  and silver compounds because their formulas are
  not ambiguous.

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Compounds of Transition Elements
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Types of Compounds Basic Concepts
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Compounds of Transition Elements
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Types of Compounds Basic Concepts
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Compounds of Transition Elements
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Types of Compounds Basic Concepts
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Hydrates

• Many ionic compounds are prepared by
  crystallization from a water solution, and water
  molecules become a part of the crystal.

• A compound in which there is a specific ratio of
  water to ionic compound is called a hydrate.

• In a hydrate, the water molecules are chemically
  bonded to the ionic compound.

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Hydrates

• Some ionic compounds can easily become hydrates
  by absorbing water molecules from water vapor in
  the air.

• These compounds are called hygroscopic
  substances, and one example is sodium carbonate
  (Na2CO3).

• In a hydrate, the water molecules are chemically
  bonded to the ionic compound.

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Hydrates

• Substances that are so hygroscopic that they take
  up enough water from the air to dissolve
  completely and form a liquid solution are called
  deliquescent.

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Hydrates

• To write the formula for a hydrate, write the
  formula for the compound and then place a dot
  followed by the number of water molecules per
  formula unit of compound.

• The dot in the formula represents a ratio of
  compound formula units to water molecules.

• For example, CaSO4 2H20 is the formula for a
  hydrate of calcium sulfate that contains two
  molecules of water for each formula unit of
  calcium sulfate.

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Hydrates

• To name hydrates, follow the regular name for the
  compound with the word hydrate, to which a prefix
  has been added to indicate the number of water
  molecules present.

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Types of Compounds Basic Concepts
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Hydrates

• The name of the compound with the formula CaSO4
  2H2O is calcium sulfate dihydrate.

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Hydrates

• Heating hydrates can drive off the water.

• This results in the formation of an anhydrous
  compoundone in which all of the water has been
  removed.

• In some cases, an anhydrous compound may have
  different color from that of its hydrate.

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Properties of Molecular Substances

• You know that ionic compounds share many
  properties.

• The properties of a molecular substancea
  substance that has atoms held together by
  covalent rather than ionic bondsare more
  variable than the properties of ionic compounds.

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Properties of Molecular Substances

• Molecular substances usually have lower melting
  points, and most are not as hard as ionic
  compounds.

• In addition, most molecular substances are less
  soluble in water than ionic compounds and are not
  electrolytes.

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Properties of Molecular Substances

• A molecule that forms when atoms of the same
  element bond together is called a molecular
  element.

• Note that molecular elements are not
  compoundsthey contain atoms of only one element.

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Properties of Molecular Substances

• When they bond together, each atom achieves the
  stability of a noble-gas electron configuration.

• Seven nonmetal elements are found naturally as
  molecular elements of two identical atoms.

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Properties of Molecular Substances

• The elements whose natural state is diatomic are

• hydrogen,

• chlorine,

• bromine,

• nitrogen,

• oxygen,

• and iodine

• fluorine,

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Properties of Molecular Substances

• Their formulas can be written as

• H2,

• Cl2,

• Br2,

• N2,

• O2,

• and I2, respectively

• F2,

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Properties of Molecular Substances

• If two chlorine atoms combine, they share a
  single pair of electrons, and each atom attains a
  stable octet configuration.

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Properties of Molecular Substances

• Two oxygen atoms share two pairs of electrons to
  form O2, and two nitrogen atoms share three pairs
  of electrons to form N2.

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Allotropes

• Although the diatomic form of oxygen, O2, is most
  common in our atmosphere, oxygen also exists as
  O3ozone.

• The structure of ozone is different from that of
  diatomic oxygen.

• It consists of three atoms of oxygen rather than
  the two atoms in diatomic oxygen.

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Allotropes

• Molecules of a single element that differ in
  crystalline or molecular structure are called
  allotropes.

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Allotropes

• The properties of allotropes are usually
  different even though they contain the same
  element.

• This is because structure can be more important
  than composition in determining properties of
  molecules.

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Allotropes

• Phosphorus has three common allotropes white,
  red, and black.

• All are formed from P4 molecules that are joined
  in different ways, giving each allotrope a unique
  structure and properties.

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Formulas and Names of Molecular Compounds

• Chemists have devised a naming system for
  molecular compounds that is based on a much
  smaller number of rules than there are compounds.

• Substances are either organic or inorganic.
  Compounds that contain carbon, with a few
  exceptions, are classified as organic compounds.

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Formulas and Names of Molecular Compounds

• Compounds that do not contain carbon are called
  inorganic compounds.

• To name these compounds, write out the name of
  the first nonmetal and follow it by the name of
  the second nonmetal with its ending changed to
  -ide.

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Naming Organic Compounds

• You have learned that most compounds that contain
  carbon are organic compounds.

• Organic compounds make up the largest class of
  molecular compounds known.

• This is because carbon is able to bond to other
  carbon atoms in rings and chains of many sizes.

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Naming Organic Compounds

• The name of even the most complex organic
  compound is based on the name of a hydrocarbon,
  an organic compound that contains only the
  elements hydrogen and carbon.