Chapter 2 - Atoms, Molecules, and Ions

Question 1

What is the difference between an Ionic Compound and a Molecular Compound?

Answer 1

An Ionic compound is comprised of ions electrostatically bounded together in a lattice-like structure, where the ions and cations bond to each other in a duplicitous manner. A Molecular compound is a discrete unit where two or more (elements or molecules) are neutrally bonded together in definite proportions.

Question 2

List the rules that can predict how elements can be combined together to form compounds.

Answer 2

1. For compounds built only from non-metals, there is no easy way to predict a formula - many rations may generate valid substances

• NO
• N₂O
• NO₂

1. For compounds built from a metal + non-metal (using ions!), the net charge of the compound must be zero.
   * Al⁺³ + O^-2 → Al₂O₃

Question 3

What are the three classes of compound nomenclature?

Answer 3

1. Ionic compounds containing an alkali metal (1A), an alkaline metal (2A), or Ag, Al, Cd, and Zn
   
   • [Name of metal] + ([Name of non-metal monatomic anion with ending changed to “ide”] OR [name of polyatomic anion])
   • Al₂O₃ → Aluminum Oxide
   • LiOH → Lithium Hydroxide
2. Ionic compounds containing a transition metal, which can carry various amounts of positive charge.
   
   • [Name of metal] + [Charge of metal in Roman Numerals] + ([Name of non-metal monatomic anion with ending changed to “ide”] OR [name of polyatomic anion])
   • FeO → Iron (II) Oxide
   • Fe₂O₃ → Iron (III) Oxide
3. Compounds containing only non-metals.
   
   • [Greek prefix (“mono” omitted)] + [Name of 1st non-metal] + [Greek prefix] + [Name of 2nd non-metal]
   • Cl₂O₇ → Dichlorine Heptaoxide
   • ClO₂ → Chlorine Dioxide

Question 4

What is the difference between a compound and a molecule?

Answer 4

A compound is a substance that is comprised of atoms of two or more elements chemically united in fixed proportions.

A molecule is an aggregate of at least two atoms in a definite arrangement held together by chemical forces.

Ex. H₂ is a molecule, but not a compound
Ex. NaCl is a compound, but not a molecule
Ex. H₂O is both a compound and a molecule​

Question 5

What is the difference between a Empirical Formula and a Molecular Formula?

Answer 5

A Molecular Formula tells you the exact number of atoms that need to be present to create the smallest unit of a substance.

An Empirical Formula tells you which atoms are present in the simplest reduced whole number ratio

Ex. Hydrazine
Molecular Formula → N₂H₄
Empirical Formula → NH₂