CHM 113: MODULE 3

Practice Q&A flashcards covering Module 3 topic areas including chemical bonds, ionic and molecular compound properties, chemical nomenclature, formula mass, Avogadro's number, and empirical/molecular formula calculations.

How do mixtures and compounds differ regarding composition and method of separation?

Mixtures consist of two or more substances physically combined with variable composition and can be separated by physical processes. Compounds consist of elements chemically bonded in fixed proportions and can only be separated by chemical reactions.

How are cations and anions formed during the ionization process?

Ionization occurs when an atom or group of atoms loses or gains electrons. Main-group metals tend to lose electrons to form positively charged cations ($+$), while main-group nonmetals tend to gain electrons to form negatively charged anions ($-$).

What are the two general types of chemical bonds and what forces create them?

Ionic bonds result from electrostatic attractions between oppositely charged ions, whereas covalent bonds result from the sharing of electron pairs between atoms.

What structural arrangement do ionic compounds adopt in the solid phase?

In the solid phase, ionic compounds form an extended three-dimensional lattice consisting of an alternating regular array of cations and anions.

Why do ionic compounds typically possess high melting and boiling points?

High melting and boiling points in ionic compounds result from the strong electrostatic attraction between their constituent cations and anions.

Under what conditions do ionic compounds conduct electricity?

Ionic compounds act as electrical insulators in the solid state, but they become electrical conductors when molten or dissolved in water.

How does the potential energy of shared electrons in a covalent bond compare to electrons in isolated atoms?

Shared electrons in a covalent bond have lower potential energy than electrons in isolated atoms.

What happens to chemical bonds when a molecular (covalent) substance melts or boils?

Covalent bonds within individual molecules are NOT broken during melting or boiling; only the weak non-bonding attractive forces between individual molecules are overcome.

What molecular representation model is shown on the far right of this diagram, and what does it represent?

The space-filling model, which represents a best estimate of how a molecule might appear if scaled to visible size.

What is the key difference between an empirical formula and a molecular formula?

An empirical formula gives the lowest whole-number ratio of atoms of each element in a compound, whereas a molecular formula gives the exact number of atoms of each element in a discrete molecule.

Which seven elements exist naturally as neutral diatomic molecules?

Hydrogen ($H_2$), Nitrogen ($N_2$), Oxygen ($O_2$), Fluorine ($F_2$), Chlorine ($Cl_2$), Bromine ($Br_2$), and Iodine ($I_2$).

According to the classification scheme for pure substances, how are elements and compounds each subclassified?

Elements are subclassified as Atomic (e.g., $Ne$) or Molecular (e.g., $O_2$), while compounds are subclassified as Molecular (e.g., $H_2O$) or Ionic (e.g., $NaCl$).

What is a polyatomic ion?

A polyatomic ion is a group of covalently bonded atoms that has gained or lost electrons, resulting in an overall net charge.

How is the variable charge of a transition metal cation indicated when naming an ionic compound?

The charge of the transition metal cation is indicated by a Roman numeral in parentheses immediately following the metal name (e.g., iron(II) for $Fe^{2+}$).

What are the steps of the Swap and Drop method for writing ionic compound formulas?

1. Write each ion symbol along with its charge. 2. Make the charge magnitude of one ion the subscript of the other ion. 3. Reduce the subscripts to the smallest whole-number ratio.

What Greek prefixes represent numbers 1 through 10 when naming binary molecular compounds?

1: mono-, 2: di-, 3: tri-, 4: tetra-, 5: penta-, 6: hexa-, 7: hepta-, 8: octa-, 9: nona-, 10: deca-. (Note: mono- is omitted on the first element).

How is a simple binary acid named if its corresponding anion ends in "-ide"?

Add the prefix "hydro-", change the anion ending "-ide" to "-ic", and add the word "acid" (e.g., chloride $Cl^-$ becomes hydrochloric acid $HCl$).

How do the oxyanion endings "-ate" and "-ite" change when naming oxyacids?

Anions ending in "-ate" change to "-ic acid", while anions ending in "-ite" change to "-ous acid".

What are the seven common strong inorganic acids?

Hydrochloric acid ($HCl$), Hydrobromic acid ($HBr$), Hydroiodic acid ($HI$), Sulfuric acid ($H_2SO_4$), Nitric acid ($HNO_3$), Perchloric acid ($HClO_4$), and Chloric acid ($HClO_3$).

How do formula mass and molar mass differ in their units and definitions?

Formula mass is the sum of atomic masses for all atoms in a chemical formula expressed in atomic mass units ($amu$), whereas molar mass is the mass in grams of one mole ($6.022 \times 10^{23}$ particles) expressed in $g\,mol^{-1}$.

What is Avogadro's number and what conversion does it perform?

Avogadro's number is $6.022 \times 10^{23}$, which converts between the number of moles and the number of individual particles (atoms, molecules, or formula units).

What is the formula for calculating the mass percent composition of an element in a compound?

$$\%\,\text{Element} = \frac{\text{number of atoms} \times \text{atomic mass}}{\text{molar mass of compound}} \times 100$$

What three steps are used to calculate the empirical formula of a compound from mass percent composition?

1. Assume a $100\,g$ sample to convert mass percentages directly to grams. 2. Convert grams of each element to moles using molar mass. 3. Divide each mole quantity by the smallest number of moles to calculate the simplest whole-number mole ratio.

How is a molecular formula calculated from an empirical formula and molecular weight?

Divide the molecular weight by the empirical formula weight to determine the whole-number multiple, then multiply each subscript in the empirical formula by that whole-number multiple.