Naming Compounds in General Chemistry; Lewis Structures

Workshop 3: Naming Compounds in General Chemistry; Lewis Structures
Part 1. Naming compounds in chemistry (nomenclature):

1. Classify the following compounds as ionic or covalent and write their names:
   a) Na3PO4
   b) PF7
   c) CuO
2. Classify the following compounds as ionic or covalent and write their chemical formulas:
   a) chromium
   (II) nitride
   b) barium nitride
   c) diphosphorous pentoxide

Part 2: Lewis structures
Lewis structures (or Lewis dot structures) are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. Looking at the Lewis structure we can determine if a molecule has polar or nonpolar bonds. However, and this important, we cannot predict whether the molecule as a whole is polar or nonpolar just by looking at the Lewis structure. This is because Lewis structures do not necessarily represent the shapes of the molecules. We will learn to predict and draw molecular shapes later in this course – in topics 10 and 11- and we will be talking about polar and nonpolar substances then.

1. Let’s start by drawing a few simple Lewis structures.
   Draw the Lewis structures for all seven diatomic elements (H2, N2, O2, F2, Cl2, Brz, 12.). Note: Even though Br and I are not in the first 3 periods it is useful to consider them here.

The Correct Answer and Explanation is :

Part 1: Naming Compounds in Chemistry (Nomenclature)

1. Classify the following compounds as ionic or covalent and write their names:

a) Na3PO4

• Type: Ionic
• Name: Sodium phosphate
  Explanation: Sodium (Na) is a metal and phosphate (PO4) is a polyatomic ion, indicating this is an ionic compound. Sodium forms a +1 ion and phosphate forms a -3 ion. The name follows the convention of naming the cation (sodium) first and the anion (phosphate) second.

b) PF7

• Type: Covalent
• Name: Phosphorus heptafluoride
  Explanation: Phosphorus (P) and fluorine (F) are both nonmetals, indicating a covalent compound. In covalent compounds, we use prefixes to denote the number of atoms present. “Hepta-” means seven, so the compound is named phosphorus heptafluoride.

c) CuO

• Type: Ionic
• Name: Copper(II) oxide
  Explanation: Copper (Cu) can form multiple oxidation states. In this case, copper is in the +2 oxidation state, as indicated by the charge balance with oxide (O), which has a charge of -2. Hence, the compound is copper(II) oxide.

2. Classify the following compounds as ionic or covalent and write their chemical formulas:

a) Chromium (II) nitride

• Type: Ionic
• Formula: Cr2N3
  Explanation: Chromium (Cr) in the +2 oxidation state (Chromium(II)) combines with nitride (N3-), forming an ionic compound. The charges balance to give the formula Cr2N3.

b) Barium nitride

• Type: Ionic
• Formula: Ba3N2
  Explanation: Barium (Ba) forms a +2 ion and nitride (N) forms a -3 ion. The formula Ba3N2 is required to balance the charges between barium and nitrogen ions.

c) Diphosphorous pentoxide

• Type: Covalent
• Formula: P4O10
  Explanation: Diphosphorous pentoxide is a covalent compound, with two phosphorus (P) atoms and five oxygen (O) atoms per phosphorus. The formula is P4O10.

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Part 2: Lewis Structures

Lewis Structures for the Seven Diatomic Elements:

1. H2 (Hydrogen)

• Lewis Structure: H-H
  Explanation: Hydrogen atoms each have 1 valence electron. They bond by sharing electrons, forming a single bond (H-H).

1. N2 (Nitrogen)

• Lewis Structure: :N≡N:
  Explanation: Nitrogen atoms each have 5 valence electrons. They form a triple bond to share electrons, with lone pairs on each nitrogen atom.

1. O2 (Oxygen)

• Lewis Structure: :O=O:
  Explanation: Oxygen atoms each have 6 valence electrons. They form a double bond, sharing electrons, with lone pairs on each oxygen atom.

1. F2 (Fluorine)

• Lewis Structure: :F-F:
  Explanation: Fluorine atoms each have 7 valence electrons. They form a single bond, sharing electrons, with lone pairs on each fluorine atom.

1. Cl2 (Chlorine)

• Lewis Structure: :Cl-Cl:
  Explanation: Chlorine atoms each have 7 valence electrons. They form a single bond, sharing electrons, with lone pairs on each chlorine atom.

1. Br2 (Bromine)

• Lewis Structure: :Br-Br:
  Explanation: Bromine atoms each have 7 valence electrons. They form a single bond, sharing electrons, with lone pairs on each bromine atom.

1. I2 (Iodine)

• Lewis Structure: :I-I:
  Explanation: Iodine atoms each have 7 valence electrons. They form a single bond, sharing electrons, with lone pairs on each iodine atom.

Explanation:
In all the diatomic elements, the atoms bond by sharing electrons to achieve a stable configuration. The number of bonds (single, double, triple) and the lone pairs of electrons are determined by the number of valence electrons each atom has and their desire to achieve a full outer shell (usually 8 electrons, except for hydrogen, which is stable with 2). The Lewis structure is a simplified way of representing the bonding and lone pairs in molecules, helping to visualize the electron distribution.