3.1 Formulae
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1. Define the molecular formula of a compound.
The number and type of different atoms present in one molecule of the compound.
2. Define the empirical formula of a compound.
The simplest whole-number ratio of the different atoms or ions present in a compound.
3. How is the charge of an ion determined for Group 1, 2, and 3 elements?
The charge is based on valency: Group 1 loses 1 electron (+), Group 2 loses 2 electrons (2+), and Group 3 loses 3 electrons (3+).
4. How is the charge of an ion determined for Group 5, 6, and 7 elements?
Group 5 gains 3 electrons (3–), Group 6 gains 2 electrons (2–), and Group 7 gains 1 electron (–).
5. What is the formula and charge for the ammonium ion?
NH4+.
6. What is the formula and charge for the hydroxide ion?
OH–.
7. What is the formula and charge for the nitrate ion?
NO3–.
8. What is the formula and charge for the sulfate ion?
SO42–.
9. What is the formula and charge for the carbonate ion?
CO32–.
10. What are the charges for the transition metals iron(II) and iron(III)?
Fe2+ and Fe3+ respectively.
11. What is the charge for a zinc ion and a silver ion?
Zinc is Zn2+ and Silver is Ag+.
12. What is the formula for aluminium oxide?
Determine the charges (Al3+, O2–), cross the charges to become subscripts, resulting in Al2O3.
13. What is the formula for iron(II) nitrate, when should brackets be used?
Use brackets for a polyatomic ion if the ratio is more than one (e.g., Fe(NO3)2).
14. State the formula for lithium fluoride.
LiF.
15. State the formula for magnesium sulfide.
MgS.
16. State the formula for calcium nitride.
Ca3N2.
17. State the formula for barium sulfate.
BaSO4.
18. State the formula for silver chloride.
AgCl.
19. In naming covalent compounds, what prefixes are used for one, two, three, and four atoms?
mono- (one), di- (two), tri- (three), and tetra- (four).
20. State the formula for carbon monoxide and carbon dioxide.
CO and CO2.
21. State the formula for sulfur trioxide.
SO3.
22. Define valency.
The number of electrons lost, gained, or shared to achieve a full outer shell.
23. What is the valency of elements in Group 4?
4.
24. Construct a word equation and symbol equation for the reaction of carbon and oxygen.
carbon + oxygen → carbon dioxide; C + O2 → CO2.
25. What do the state symbols (s), (l), (g), and (aq) represent?
(s) solid, (l) liquid, (g) gas, and (aq) aqueous solution.
26. State the principle of conservation of mass in a chemical reaction.
The mass of any one element at the beginning of a reaction equals the mass of that element at the end of the reaction.
27. In what form are metals and non-metals typically written in a chemical equation?
Metals are written in atom form (e.g., Fe, Na), while non-metals are often in molecule form (e.g., O2, Cl2, H2).
28. Balance the equation for the formation of water: H2 + O2 → H2O.
2H2 + O2 → 2H2O.
29. Balance the equation for the formation of ammonia: N2 + H2 → NH3.
N2 + 3H2 → 2NH3.
30. Balance the equation for the reaction between sodium hydroxide and sulfuric acid.
2NaOH + H2SO4 → Na2SO4 + 2H2O.