Chapter #3 "Molecules and Compounds"

What is a chemical bond?

A chemical bond is the attractive force that holds atoms together in a compound.

How do chemical bonds relate to mixtures and compounds?

In a mixture, elements can combine in any arbitrary ratio, while in a compound, atoms are held together by chemical bonds in a fixed, definite ratio.

What is an ionic bond?

An ionic bond is a chemical bond formed between metals and nonmetals, characterized by the transfer of electrons.

What are the steps in the process of forming an ionic bond?

Step 1: A neutral metal atom transfers electrons to a neutral nonmetal atom. Step 2: The metal atom becomes a positively charged cation, and the nonmetal atom becomes a negatively charged anion. Step 3: The oppositely charged ions attract each other to form a crystalline lattice.

How does the ionic bond relate to cations and anions?

The transfer of electrons creates cations (positively charged ions) and anions (negatively charged ions), and the ionic bond is the attraction between them.

What is a formula unit?

A formula unit is the smallest electrically neutral ratio of ions in an ionic compound.

What is an example of a formula unit?

The formula unit for table salt is NaCl, containing 1 Na⁺ ion and 1 Cl⁻ ion.

What is a covalent bond?

A covalent bond is a chemical bond that occurs between two or more nonmetals, where atoms share electrons.

What are the steps in the process of forming a covalent bond?

Step 1: Nonmetal atoms approach each other, and their electron clouds overlap. Step 2: Atoms share one or more pairs of valence electrons. Step 3: The shared electrons are attracted to the nuclei of both atoms.

What are molecular compounds?

Compounds formed via covalent bonds are called molecular compounds because their basic units are discrete molecules.

What is a chemical formula?

A chemical formula indicates the specific elements present in a compound and the relative number of atoms of each element.

What is an empirical formula?

An empirical formula gives the simplest, relative whole-number ratio of atoms of each element in a compound.

What are the steps to determine an empirical formula?

Step 1: Determine the relative number of moles of each element. Step 2: Express these amounts as a ratio. Step 3: Divide by the smallest value to find the simplest whole-number ratio.

What is a molecular formula?

A molecular formula gives the actual number of atoms of each element in a molecule of a compound.

What are the steps to determine a molecular formula?

Step 1: Determine the empirical formula. Step 2: Find the molar mass of the compound. Step 3: Divide the molar mass by the empirical formula mass to find the multiplying factor. Step 4: Multiply all subscripts in the empirical formula by this factor.

What is the relationship between empirical and molecular formulas?

The molecular formula is always a whole-number multiple of the empirical formula.

What is a structural formula?

A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected.

How do structural formulas relate to molecular models?

Structural formulas show 2D connectivity, while molecular models are 3D representations showing spatial arrangements.

What is a ball-and-stick model?

A ball-and-stick model represents atoms as balls and chemical bonds as sticks, reflecting the molecule's overall shape.

What is a space-filling model?

A space-filling model shows atoms filling the space between each other, providing an accurate estimate of a molecule's appearance.

What are atomic elements?

Atomic elements exist as single atoms under normal conditions.

What are examples of atomic elements?

Examples include Na, He, Ne, and Ar.

What are molecular elements?

Molecular elements exist as molecules made of two or more atoms of the same element.

What are examples of molecular elements?

Examples include H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂, P₄, and S₈.

How do atomic and molecular elements differ?

Atomic elements exist as free, single atoms, while molecular elements consist of diatomic or polyatomic molecules.

Why are certain atoms diatomic or polyatomic?

These atoms are reactive as isolated monomers and require bonding to achieve stable electron configurations.

How can you determine which elements are diatomic?

The seven diatomic elements are H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂.

What is an example of a molecular compound?

An example is CO₂ (carbon dioxide).

What are ionic compounds?

Ionic compounds are formed from metal cations and nonmetal anions held together by ionic bonds.

What is an example of an ionic compound?

An example is NaCl (sodium chloride).

How do molecular and ionic compounds differ?

Molecular compounds feature shared electrons, while ionic compounds involve transferred electrons.

What is an ionic compound?

An ionic compound is a neutral substance composed of cation and anion arrays held together by electrostatic attractions.

How do ionic compounds relate to atomic and molecular elements?

Ionic compounds form when metal atomic elements react with nonmetal elements.

How is the chemical formula of an ionic compound represented?

It is represented as a formula unit, showing the smallest whole-number ratio of ions.

What are the steps to determine the chemical formula of an ionic compound?

Step 1: Write the symbol for the metal cation followed by the nonmetal anion. Step 2: Use the criss-cross method for subscripts. Step 3: Reduce subscripts to the smallest ratio.

What are the distinct categories of ionic compounds?

Type I: Fixed charge metals. Type II: Variable charge metals.

How do Type I and Type II ionic compounds differ?

Type I compounds have a constant charge, while Type II compounds have variable charges that must be specified.

What are binary compounds?

Binary compounds contain only two different elements.

How does naming work for Type I binary ionic compounds?

Step 1: Write the name of the metal cation. Step 2: Write the name of the nonmetal anion with -ide ending.

What are Type II binary compounds?

They are binary compounds consisting of a transition metal and a nonmetal.

How does naming work for Type II binary ionic compounds?

Step 1: Determine the charge of the metal cation. Step 2: Write the name of the metal cation.

What is a monoatomic ion?

An ion consisting of a single atom that has gained or lost electrons.

What are examples of monoatomic ions?

Na⁺ (sodium ion) and Cl⁻ (chloride ion).

How do you name cations?

State the name of the element followed by the word 'ion' or include Roman numerals if it is Type II.

How do you name anions?

Use the root name of the element and change the ending to -ide.

What is a polyatomic ion?

An ion composed of two or more covalently bonded atoms that carry an overall net electrical charge.

How do you name ionic compounds with polyatomic ions?

Use the same guidelines as binary compounds, substituting the specific name of the polyatomic ion.

How would you name NaNO₂?

Sodium nitrite.

What are hydrates?

Ionic compounds that contain a specific number of water molecules weakly bound within their crystalline formula units.

What are the hydrate prefixes?

1 = mono-, 2 = di-, 3 = tri-, 4 = tetra-, 5 = penta-, 6 = hexa-, 7 = hepta-, 8 = octa-, 9 = nona-, 10 = deca-.

How would you name CuSO₄ • 5 H₂O?

Copper(II) sulfate pentahydrate.

How do molecular compounds differ from ionic compounds?

They consist of shared electrons and discrete molecules rather than ionic lattices.

How do you name a molecular compound?

1. Write the name of the first element. 2. Use Greek prefixes to indicate the number of atoms. 3. Name the second element, changing its ending to -ide.

What is CO₂?

Carbon dioxide.

What is N₂O₅?

Dinitrogen pentoxide.

What is P₄S₁₀?

Phosphorus decasulfide.

What are acids?

Molecular compounds that release hydrogen ions (H⁺) when dissolved in water.

What are binary acids?

Acids composed of hydrogen and only one other nonmetal element.

How do you name binary acids?

1. Add the prefix hydro- to the root of the nonmetal's name. 2. Add the suffix -ic. 3. Add the word acid.

What is hydrochloric acid?

HCl(aq) is hydrochloric acid.

What are oxyacids?

Acids that contain hydrogen combined with an oxygen-containing polyatomic ion.

How do you name oxyacids?

1. Identify the polyatomic oxyanion. 2. If it ends in -ate, change to -ic and add 'acid'. 3. If it ends in -ite, change to -ous and add 'acid'.

What is sulfuric acid?

H₂SO₄(aq) contains sulfate (SO₄²⁻), making it sulfuric acid.

What is acetic acid?

HC₂H₃O₂(aq) contains acetate (C₂H₃O₂⁻), making it acetic acid.

How is formula mass calculated?

By adding up the atomic masses of all individual atoms in the chemical formula.

What is the equation for formula mass?

Formula Mass = Σ (Number of atoms of element i × Atomic mass of element i).

How do you find the formula mass of H₂O?

(2 × 1.01 amu) + (1 × 16.00 amu) = 18.02 amu.

What is the molar mass of a compound?

The mass of 1 mole of its molecules or formula units.

How can you find the number of molecules in a compound?

1. Measure the mass in grams. 2. Convert to moles by dividing by molar mass. 3. Multiply by Avogadro's number.

How does molar mass compare between elements and compounds?

Element molar mass is for individual atoms, while compound molar mass is for bonded formula units.

What is mass percentage?

An element's percentage of the total overall mass of the compound.

What is the equation for mass percentage?

Mass % of Element = (Mass of Element in 1 mol of Compound ÷ Mass of 1 mol of Compound) × 100%.

How can you determine an empirical formula?

1. Convert mass percentages to grams. 2. Convert grams to moles. 3. Write a pseudoformula. 4. Divide by the smallest subscript. 5. Round or multiply to get whole numbers.

What is the empirical formula for C 60.00%; H 4.48%; O 35.52%?

C₉H₈O₄.

What is the molecular formula?

The formula indicating the actual number of each atom present in a single molecule.

How does the molecular formula relate to the empirical formula?

The molecular formula is a whole-number multiple of the empirical formula.

How can you determine the molecular formula?

1. Find the empirical formula. 2. Calculate its formula mass. 3. Divide the molar mass by the empirical formula mass. 4. Multiply subscripts by the whole-number multiplier.