Ionic Compounds

1
Ionic Compounds

• Unit 6

2
Writing Formulas

• Elements occur in constant whole number ratios in
  a compound (Law of Definite Proportions).
• In a chemical formula symbols and subscripts are
  used to describe this ratio.
• For molecules the chemical (molecular) formula
  shows the actual number of atoms of each element
  in the compound
• In an ionic compound, the formula shows the
  lowest whole number ratio of ions in the ionic
  crystal.
• This ratio is called a formula unit.

3
Identifying Ionic Compounds

• Any substance made of metal cation and nonmetal
  anion OR contains any polyatomic ions
• Ionic bond transfer of electrons
• 1 atom loses, 1 atom gains (cation/anion formed)
• the and particles are attracted to one anther
  and form a very stable bond (electrostatic
  attract.)
• Properties of ionic bonds
• high melting point
• low malleability break and shatter easily
• can conduct electricity under certain conditions
• Coordination number the number of ions of
  opposite charge that surround the ion in a
  crystal

4
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5
Naming Ionic Compounds

• Simply name the two ions, positive ion first (the
  positive ion is always first).
• Positive monatomic (one type of element) ions
  have the same name as the element.
• Na ? sodium ion
• Al3? aluminum ion

6
Naming Ionic Compounds

• Negative monatomic ions end in ide.
• Cl-? chloride ion
• O2-? oxide ion
• Negative polyatomic ions end in ate or ite.
• There is not a hard and fast rule which will
  allow you to determine if a polyatomic ion is
  ate or ite (which is why you have to memorize
  them), but there is one helpful shortcut.

7
Patterns for Polyatomic Ions

• The most common form of a polyatomic ion formed
  from a nonmetal combined with oxygen ends in
  ate.
• -ate ion
• chlorate ClO3-
• -ate ion plus 1 O Þ same charge, per- prefix
• perchlorate ClO4-
• -ate ion minus 1 O Þ same charge, -ite suffix
• chlorite ClO2-
• -ate ion minus 2 O Þ same charge, hypo- prefix,
  -ite suffix
• hypochlorite ClO-

8
Patterns for Polyatomic Ions

• Elements in the same column on the Periodic Table
  form similar polyatomic ions
• same number of Os and same charge
• ClO3- chlorate \ BrO3- bromate
• If the polyatomic ion starts with H, add
  hydrogen- before the ions name and add 1 to the
  charge
• CO32- carbonate \ HCO3- hydrogen carbonate

9
Writing Ionic Formulas

• IMPORTANT When writing formulas, use
  appropriate subscripts so the total number of
  positive and negative charges cancel out and the
  compound is neutral.
• Now, lets see how good we are at writing some
  formulas and naming some ionic compounds.

10
Practice

• KBr
• Since this has a metal (K) and a nonmetal (Br),
• we say it is an ionic compound.
• So we name the positive ion potassium and the
  negative ion with the ending changed to ide,
  bromide.
• Potassium bromide
• Binary compound

11
Practice

• Calcium Chloride
• Again a metal and a nonmetal so it is ionic.
• Calcium would form an ion with a 2 charge
• and chloride would be 1-.
• Ca2Cl- ? in order for the compound to be
  neutral, how many Cl- would there need to be for
  every Ca2??
• 2 Cl- for every 1 Ca2
• So the formula would be CaCl2
• Binary compound

12
Practice

• Na2CO3
• In this compound there are two ways to identify
  is as ionic.
• First, it has a metal and a nonmetal.
• Second, it has a polyatomic ion.
• So we name the ions, positive ion first.
• Sodium carbonate
• Ternary compound

13
Practice

• Magnesium Phosphate
• magnesium Mg2 phosphate PO43-
• In order for the compound to be neutral we have
  to find the least common multiple between our two
  charges, 2 and 3. The LCM is 6.
• 2 goes into 6 3 times so Mg3 3 goes into 6 2
  times so (PO4)2.
• 3 x 2 6 AND 2 x -3 -6
• Our compound is neutral.
• Mg3(PO4)2
• Ternary compound

14
Important Precautions

• If we need more than one polyatomic ion (like in
  the previous example), it must be surrounded by
  parentheses before you add the subscript.
• Also, notice that if the subscript is 1 we do not
  write it.
• If the positive ion has more than one possible
  oxidation number, then when we write the name we
  must indicate which oxidation state it is.
• This is done by writing a roman numeral in
  parentheses which is equal to the positive charge.

15
Practice

• Copper (I) Oxide
• (I) indicates that the copper has a charge of 1.
• Copper - Cu1 Oxide O2-
• Cu2O
• Iron (III) Oxide
• (III) indicates iron has a 3 charge.
• Iron - Fe3 Oxide O2-
• Fe2O3
• Practice and More Practice!!!

16
Naming Hydrates

• Hydrates are crystalline compounds which attract
  and hold water molecules.
• The water is called the water of hydration and
  can be removed (evaporated) by heating.
• After water is removed the crystal is said to be
  anhydrous.

17
Naming Hydrates

• To name hydrates simply name the compound
  (usually ionic) and then indicate the number of
  water molecules by using the same prefixes as in
  molecular compounds.
• CuSO4 5 H2O
• Copper (II) sulfate pentahydrate
• Sodium carbonate heptahydrate
• Na2CO3 7 H2O

18
Number Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
19
Bonding In Metals

• valence electrons of metal atoms can be modeled
  as a sea of electrons they are mobile and can
  drift from one part of the metal to the other
• Metallic Bond the attraction of these
  free-floating electrons for the metal ions
• these bonds hold metals together and explain many
  of their physical properties
• but can we actually bond 2 metals together?

20
Alloys

• an alloy is a MIXTURE that is composed of two or
  more elements, at least one of which is a metal
• you can also think of an alloy as a solid
  solution made by dissolving metals in other
  metals
• alloys are important because their properties are
  often superior to those of their component
  elements

21
Substitutional Alloy

• atoms of approximately the same size replace each
  other in the crystal
• sterling silver, coins, solder, brass, 18-carrat
  gold, bronze

22
Interstitial Alloy

• atoms of smaller size fit into the space
  (interstices) between the larger atoms
• cast iron, steel, stainless steel, surgical steel

23
Amalgam

• metal solution that contains mercury
• this type of alloy may be a solid or liquid
• used to be very useful in dental amalgams
  (mixture of Hg, Ag, and Zn)