Chemistry 30
Miss Mayer
Naming and Writing Formulas Review
Bonds
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Remember that atoms can be combined to make molecules or compounds. Bonds connect atoms
together.
The valence shell electrons actually determine how many of each element will combine to make a
compound. They represent the number of electrons that will be shared, transferred or accepted between
elements to form a stable compound.
There are 2 different types of bonds:
1. Ionic Bonds: formed when metals transfer their electron(s) to non-metals
2. Covalent Bonds: formed when electrons are shared between two non-metals.
Naming Compounds
Ionic compounds:
 The first element (the metal ion) in the compound does not change its name.
 The second element (the non-metal ion) drops its ending and adds “-ide”
 Metals that can have more than one charge: use a roman numeral in brackets to indicate the charge
 Use a table for the names of polyatomic ions. Do not change endings!
o Examples:
LiCl = lithium chloride
FeCl2 = iron (II) chloride
NaNO3 = sodium nitrate
Covalent/Molecular compounds:
 The second element still drops its ending and adds “-ide”
 Use prefixes to indicate the number of each element in the compound.
 ***Mono is never used on the first element.
o Examples:
N2O3 = dinitrogen trioxide
SiO2 = silicon dioxide
Naming acids:
Acids are covalent compounds formed when hydrogen combines with non-metal or polyatomic ions. The
hydrogen is always written first in the compound and the naming is based on what the anion’s (negative ion)
name ends in: -ide, -ite or -ate.
Naming acids with anions that end in –ide (for the most part, anions from the PTE):
 Use the prefix “hydro” followed by the name of the anion which has dropped its ending and
added “ic” to it.
 The second word is “acid”.
o Example: HF is hydrofluoric acid (from the anion fluoride)
o Example: HCN is hydrocyanic acid (from the anion cyanide)
Naming acids with polyatomic anions that end in –ate or –ite:
 The first word is the polyatomic anion which has dropped its ending and added either
o –ic if the anion name ends in –ate
o –ous if the anion name ends in -ite
 the second word is “acid”
o Examples: H2SO4 is sulfuric acid (from the anion sulfate)
HClO3 is perchlorous acid (from the anion perchlorite)
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Chemistry 30
Miss Mayer
Name the following compounds and indicate if each is an ionic compound, an acid or a covalent
compound.
Name
Ionic, Acid or Covalent?
1. KNO3
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2. CO2
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3. H2SO4
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4. Pb(NO3)4
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5. Ca(OH)2
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6. FeCl3
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7. CaCl2
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8. HCl
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9. P2O3
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10. CCl4
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11. H2CO3
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12. H2CO2
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13. (NH4)2S
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14. MgBr2
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15. SeF2
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Chemistry 30
Miss Mayer
Writing Formulas
1. Ionic Compounds (metals and non-metals):
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Positive ion written first, negative ion second.
The sum of the charges will be zero because ions add on until a neutral molecule is formed
SHORTCUT: You can criss-cross charge values by writing the number behind and below the
opposite element. If only one atom is needed, you do not write the subscript 1. Charges of the
same value just cancel out. (+1/-1, +2/-2 etc).
Roman numerals are used with metals that make more than one charge. The number indicates
the charge, NOT how many atoms are in that compound!
Use the tables provided for charges of ions and for polyatomic ions (ions that, as a group of
atoms, hold a charge).
If there are more than one polyatomic ion needed, use brackets.
Reduce your formula to its lowest form.
Examples:
 Sodium chloride  Na1+, Cl1- = NaCl
 Calcium chloride  Ca2+, Cl1- = CaCl2
 Iron (III) oxide  Fe3+, O2- = Fe2O3
 Aluminum sulfate  Al3+, SO42- = Al2(SO4)3
 Tin (IV) sulfate  Sn4+, SO42- = Sn(SO4)2
(charges cancel)
(criss-cross numbers)
(roman numeral indicates 3+)
(polyatomic ion)
(reduce from Sn2(SO4)4)
2. Covalent/Molecular compounds (two non-metals)



Write the compound by ignoring the charges and writing exactly what the name states
NEVER reduce formulas.
NOTE: we never use mono for the first element!
Examples:
 Nitrogen dioxide  NO2
 Carbon monoxide  CO
 Diphosphorous pentaoxide  P2O5
 Disilicon tetroxide  Si2O4 (don’t reduce!)
3. Formulas for Acids
Acids are covalent compounds formed when hydrogen combines with non-metal or polyatomic ions.
Even though they are covalent, the formulas are calculated the same way as with ionic compounds; just
criss-cross the charges. However, there are three rules to remember:
I.
If the prefix “hydro” is used in the name, it is hydrogen bonding with a non-metal off the
periodic table (or a polyatomic ion that ends in –ide).
 Ex. hydrofluoric acid is HF; hydrogen 1+ and fluoride 1 Ex. Hydrocyanic acid is HCN; hydrogen 1+ and cyanide 1II.
If the name ends in –ic, a polyatomic anion with the ending –ate was used. Use your sheet!
 Ex. Sulfuric acid is H2SO4; hydrogen 1+ and sulfate 2III.
If the name ends in –ous, a polyatomic anion with the ending –ite was used. Use your sheet!
 Ex. Perchlorous acid is HClO3; hydrogen1+ and perchlorite13
Chemistry 30
Miss Mayer
Write the correct formula for the following:
I/C/A
Formula
1. carbon tetrachloride
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2. hypochlorous acid
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3. barium phosphate
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4. iron (III) nitrate
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5. potassium permanganate
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6. diphosphorus trioxide
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7. beryllium nitride
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8. silicon dioxide
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9. sodium nitride
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10. ammonium nitrite
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11. boric acid
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12. calcium thiocyanate
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13. dinitrogen triselenide
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14. arsenic trifluoride
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15. hydroselenic acid
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16. nickel (II) phosphite
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17. carbonic acid
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18. aluminum chloride
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19. manganese (IV) oxide
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20. chromous acid
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21. strontium nitride
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22. hydronitric acid
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23. lithium chromate
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24. hydrosulfuric acid
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25. antimony (V) phosphide
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26. tin (II) bromide
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27. sulfurous acid
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28. copper (I) iodide
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29. phosphoric acid
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30. oxalic acid
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