SNC2D1 Chemistry Notes: Molecules & Binary Molecular Compounds

Chemistry Notes for SNC2D1 – Molecules & Binary Molecular Compounds

Basic Definitions

• Molecule: A group of two or more non-metal atoms joined together with a covalent bond. This can include either a diatomic element or a molecular compound.

Diatomic Molecule

• Diatomic Molecule: A molecule that consists of two atoms of the same or different elements joined with a covalent bond.

Diatomic Elements

• Diatomic Elements: These are diatomic molecules consisting of the same element. They are not classified as compounds.

• List of Diatomic Elements:

  • Element Name: hydrogen
    Chemical Symbol: H
    Formula of Molecule: H₂
    State at Room Temperature: gas

  • Element Name: oxygen
    Chemical Symbol: O
    Formula of Molecule: O₂
    State at Room Temperature: gas

  • Element Name: fluorine
    Chemical Symbol: F
    Formula of Molecule: F₂
    State at Room Temperature: gas

  • Element Name: bromine
    Chemical Symbol: Br
    Formula of Molecule: Br₂
    State at Room Temperature: liquid

  • Element Name: iodine
    Chemical Symbol: I
    Formula of Molecule: I₂
    State at Room Temperature: solid

  • Element Name: nitrogen
    Chemical Symbol: N
    Formula of Molecule: N₂
    State at Room Temperature: gas

  • Element Name: chlorine
    Chemical Symbol: Cl
    Formula of Molecule: Cl₂
    State at Room Temperature: gas

Molecular Compounds

• Definition: A molecular compound is a substance that consists of non-metal anions. The bond forming these compounds is called a covalent bond. The bonded atoms create a molecule through shared electrons.

• Electron Sharing: Electrons are shared between the two non-metal atoms involved. This allows the valence shells of the bonding atoms to interact, facilitating each atom to achieve a full valence shell of 8 electrons, adhering to the Octet Rule.

Naming and Writing Formulas for Molecular Compounds

• Order of Elements: When naming a compound or deriving the formula, the element that is furthest to the left on the periodic table is always listed first.

• Suffix for Second Element: The second element in the compound’s name always ends with '-ide'. For instance, iodine becomes 'iodide'.

• Greek Prefixes Usage: Greek prefixes indicate the number of atoms present for each element. Some elements possess more than one combining capacity. It’s important to note that if there is only one atom of the first element in a molecular compound, the prefix “mono” is omitted.

Greek Prefixes

• 1: mono-

• 2: di-

• 3: tri-

• 4: tetr(a)-

• 5: pent(a)-

• 6: hex(a)-

• 7: hept(a)-

• 8: oct(a)-

• 9: non(a)-

• 10: Dec(a)-

Examples of Naming Compounds

Example #1: Name the compounds from the chemical formulas

• Chemical Formula: NO
  Chemical Name: nitrogen monoxide

• Chemical Formula: CO₂
  Chemical Name: carbon dioxide

• Chemical Formula: P₂O₅
  Chemical Name: diphosphorus pentoxide

• Chemical Formula: Cl₃
  Chemical Name: trichlorine

• Chemical Formula: IF₄
  Chemical Name: iodine tetrafluoride

Example #2: Writing the Chemical Formula and Naming Given Non-Metals

1. Carbon and Fluorine

   • Chemical Formula: CF₄

   • Chemical Name: carbon tetrafluoride

2. Nitrogen and Chlorine

   • Chemical Formula: NCl₃

   • Chemical Name: nitrogen trichloride

3. Silicon and Nitrogen

   • Chemical Formula: Si₃N₄

   • Chemical Name: silicon nitride

Example #3: Writing the Chemical Formula from Compound Names

• Step 1: Examine the name of the molecular compound; e.g., dinitrogen tetroxide.

• Step 2: Use the periodic table to find the symbols for the elements.

  • nitrogen = N

  • oxide = oxygen = O

• Step 3: Analyze the prefixes to determine the number of atoms for each element.

  • di = 2

  • tetra = 4

• Step 4: Write in the chemical formula using subscripts accordingly. The resulting formula is:

  • Formula: N₂O₄.

• Important Note: Do not reduce the subscripts when converting compound names into chemical formulas.