40 Questions
What type of molecule contains more than two atoms?
Polyatomic molecule
What determines the order of elements in a molecular compound?
The group number of the elements
Which of the following is an example of a binary molecular compound?
N2O3
What is the name of the process of naming molecular compounds?
Nomenclature
Why is the prefix mono- generally omitted for the first element?
For ease of pronunciation
What is the purpose of using Greek prefixes in naming binary molecular compounds?
To specify the number of atoms of each element
What is the correct order of elements in a molecular compound?
Element with smallest group number first
What is special about the naming of oxides?
The last letter of the prefix is eliminated
Why is NCl3 named nitrogen trichloride, but AlCl3 is simply aluminum chloride?
NCl3 is a molecular compound and AlCl3 is an ionic compound
What type of compound is CoCI2 · 6H2O?
Hydrated ionic compound
What is the systematic name for MgSO4 · 7H2O?
Magnesium sulfate heptahydrate
What is the meaning of the prefix 'hemi' in hydrate prefixes?
Half a water molecule
What is the name of the prefix that represents three water molecules in hydrate prefixes?
Tri
What type of compound is CaSO4 · ½H2O?
Hydrated ionic compound
What is the systematic name for CaSO4 · ½H2O?
Calcium sulfate hemihydrate
What is the general formula for a hydrated ionic compound?
MX · xH2O
What is the prefix for the number 9 in binary molecular compounds?
Nona-
What is the name of the compound CO2?
Carbon dioxide
What is the correct name of the compound P4S10?
Tetraphosphorus decasulfide
What is the correct formula for phosphorus tribromide?
PBr3
What is the name of the compound NI3?
Nitrogen triiodide
What is the prefix for the number 5 in binary molecular compounds?
Penta-
What is the name of the compound SF6?
Sulfur hexafluoride
What is the name of the compound PCI5?
Phosphorus pentachloride
What is the definition of an acid?
A substance that produces hydrogen ions when dissolved in water
What is the rule for naming simple acids?
Replace the -ide ending with -ic and add the word acid
What is the name of the acid derived from the oxoanion chlorate?
Chloric acid
How is the name of an oxoacid derived when the oxoanion’s name ends in -ite?
The ending changes to -ous and the word acid is added
What is the name of the acid derived from the oxoanion perchlorate?
Perchloric acid
What is the mass of carbon in 100 g of a compound with 53.31% carbon?
53.31 g
What is the name of the acid derived from the oxoanion chlorite?
Chlorous acid
What is the general structure of an acid?
Hydrogen ions attached to an anion
What is the number of moles of hydrogen in 11.19 g of hydrogen?
11.10 mol
What is the rule for deriving the name of an oxoacid when the oxoanion’s name ends in -ate?
The ending changes to -ic and the word acid is added
What is the smallest number of moles in the preliminary result of C4.439H11.10O2.219?
2.219
What is the empirical formula of a compound with a mass percent composition of 53.31% carbon, 11.19% hydrogen, and 35.51% oxygen?
C2H5O
What is the molar mass of oxygen?
16.00 g/mol
What is the purpose of dividing each of the numerical results by the smallest number of moles?
To reduce the subscripts to whole numbers
What is the number of moles of carbon in 53.31 g of carbon?
4.439 mol
What is the result of dividing each of the numerical results by the smallest number of moles?
C2H5O
Study Notes
Molecules and Molecular Compounds
- A molecule can be of an element (e.g., Cl2, H2) or a compound (e.g., HCl)
- Diatomic molecules contain two atoms (e.g., HCl, CO, N2)
- Polyatomic molecules contain more than two atoms (e.g., O3, H2O)
Molecular Compounds: Formulas and Names
- The formula for a molecular compound cannot be readily determined from its constituent elements
- Many different combinations of elements can form unique molecular compounds (e.g., NO, NO2, N2O, N2O3, N2O4, N2O5)
- Binary molecular compounds are composed of two nonmetals
- To name the compound, name the element that appears first in the formula, then the second element, changing the ending of its name to -ide
Naming Binary Molecular Compounds
- Use Greek prefixes to specify the number of atoms of each element present (e.g., mono- = 1, di- = 2, tri- = 3, tetra- = 4, penta- = 5, hexa- = 6)
- If there is only one atom of the first element in the formula, the prefix mono- is normally omitted
- Examples of named compounds:
- SF6: sulfur hexafluoride
- CF4: carbon tetrafluoride
- CO2: carbon dioxide
- N2O5: dinitrogen pentoxide
Problem Solving: Naming Molecular Compounds
- Example 1: NI3 (nitrogen triiodide)
- Example 2: PCI5 (phosphorus pentachloride)
- Example 3: P4S10 (tetraphosphorus decasulfide)
Hydrated Ionic Compounds
- Hydrates are ionic compounds containing a specific number of water molecules associated with each formula unit
- Examples:
- MgSO4 · 7H2O (magnesium sulfate heptahydrate)
- CoCI2 · 6H2O (cobalt(II) chloride hexahydrate)
Acids
- An acid is any substance that produces hydrogen ions (H+) when dissolved in water
- Acids are molecular compounds, but can be thought of as hydrogen ions attached to an anion
- Rules for naming simple acids:
- Remove the -gen ending from hydrogen (leaving hydro-)
- Change the -ide ending on the anion to –ic
- Combine the two words, and add the word acid
- Examples:
- HF: hydrofluoric acid
- HCl: hydrochloric acid
- HBr: hydrobromic acid
- HI: hydroiodic acid
- HCN: hydrocyanic acid
- H2S: hydrosulfuric acid
Empirical Formula
- Example: Determine the empirical formula of a compound with a mass percent composition of 53.31% carbon, 11.19% hydrogen, and 35.51% oxygen
- Calculate the number of moles of each element, then reduce the subscripts to whole numbers to obtain the empirical formula, which in this case is C2H5O
Learn about molecules and molecular compounds, including their structure and formulas. Understand the difference between diatomic and polyatomic molecules.
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