CHM1045 Exam 2 basics

What is a limiting reactant?

The reactant that is completely consumed first, limiting the amount of product formed.

What is an excess reactant?

A reactant present in greater quantity than needed, so some remains after the reaction

Why are balanced chemical equations important in stoichiometry?

They show the mole ratios needed to calculate reactant and product amounts.

How do you identify the limiting reactant?

Compare the mole ratio of reactants available to the mole ratio required by the balanced equation.

Formula: Mole Conversion (grams → moles)

moles = mass ÷ molar mass

Formula: Mole Conversion (moles → grams)

mass = moles × molar mass

Formula: Speed of Light

c = λν, where c = 3.00 × 10⁸ m/s

Formula: Energy of a photon

E = hν, where h = 6.626 × 10⁻³⁴ J·s

Formula: Energy in terms of wavelength

E = hc ÷ λ

What is the formula for percent yield?

% yield = (actual yield ÷ theoretical yield) × 100

Why is the actual yield often less than the theoretical yield?

Because of side reactions, incomplete reactions, or loss of product during collection.

What happens when an electron moves from a higher to a lower energy level?

A photon of specific energy (and wavelength) is emitted.

What is the de Broglie hypothesis?

Particles such as electrons have wave-like properties with wavelength λ = h/mv.

How are energy and frequency related?

E = hν (Planck’s equation).

What does the principal quantum number (n) represent?

The size and energy level of an orbital.

What does the angular momentum quantum number (l) describe?

The shape of the orbital (s, p, d, f).

What does the magnetic quantum number (ml) indicate?

The orientation of an orbital in space.

What is the Bohr model of the atom?

Electrons orbit the nucleus in fixed energy levels (quantized orbits).

Formula: Bohr energy levels for hydrogen

En = –2.18 × 10⁻¹⁸ J (Z² ÷ n²)

What is Planck’s constant (h)?

6.626 × 10⁻³⁴ J·s

Allowed values of l?

0 to (n – 1).

What orbital shape corresponds to l = 0?

s orbital (spherical).

What orbital shape corresponds to l = 1?

p orbital (dumbbell-shaped).

What orbital shape corresponds to l = 2?

d orbital (clover-shaped).

What does the spin quantum number (ms) represent?

Electron spin, either +½ or –½.

What is the Pauli Exclusion Principle?

No two electrons can have the same set of four quantum numbers.

What is Hund’s Rule?

Orbitals of equal energy are filled singly before pairing.

What is the Heisenberg Uncertainty Principle?

It is impossible to know both position and momentum of an electron precisely.

What is the Aufbau Principle?

Electrons fill the lowest energy orbitals first.

Formula for effective nuclear charge (Zeff)?

Zeff = Z – shielding electrons

How does atomic radius change across a period?

Decreases due to greater effective nuclear charge.

How does atomic radius change down a group?

Increases due to additional electron shells.

What is ionization energy?

The energy required to remove an electron.

How does ionization energy trend across the periodic table?

Increases across a period, decreases down a group.

What is electron affinity?

The energy change when an atom gains an electron.

How does electron affinity trend across the table?

What is electronegativity?

An atom’s ability to attract shared electrons in a bond.

Electronegativity trend across the periodic table?

Increases across a period, decreases down a group

What is an isoelectronic series?

Ions/atoms with the same electron configuration but different nuclear charges.

In an isoelectronic series, how does ionic radius change with increasing nuclear charge?

The radius decreases.

What are cations compared to their parent atoms?

Smaller, because they lose electrons.

What are anions compared to their parent atoms?

Larger, because they gain electrons and have more repulsion.

What is an ionic compound?

A compound of cations and anions held by electrostatic attraction.

What is a polyatomic ion?

group of covalently bonded atoms with a net charge.

How do you name binary ionic compounds?

Cation + anion with -ide ending.

How do you name ionic compounds with type 2 metals?

Use Roman numerals to indicate charge.

What is the difference between -ate and -ite oxyanions?

-ate has more oxygen atoms, -ite has fewer.

What is the overall charge of an ionic compound?

Neutral.

What does "isoelectronic" mean in terms of ions?

What does "isoelectronic" mean in terms of ions?

NH₄⁺

Ammonium

OH⁻

Hydroxide

NO₃⁻

Nitrate

NO₂⁻

Nitrite

SO₄²⁻

Sulfate

SO₃²⁻

Sulfite

CO₃²⁻

Carbonate

HCO₃⁻

Bicarbonate (hydrogen carbonate)

PO₄³⁻

Phosphate

PO₃³⁻

Phosphite

ClO⁻

Hypochlorite

ClO₂⁻

Chlorite

ClO₃⁻

Chlorate

ClO₄⁻

Perchlorate

BrO₃⁻

Bromate

BrO₄⁻

Perbromate

CN⁻

Cyanide

C₂H₃O₂⁻ (CH₃COO⁻)

Acetate

MnO₄⁻

Permanganate

CrO₄²⁻

Chromate

Cr₂O₇²⁻

Dichromate

How are atoms bonded in molecular compounds?

By sharing electrons through covalent bonds.

What is a single covalent bond?

A bond formed when two atoms share one pair of electrons.

What is a molecular formula?

It shows the actual number and kinds of atoms in a molecule.

What is an empirical formula?

The simplest whole-number ratio of atoms in a compound.

How does a molecular formula relate to an empirical formula?

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

What are binary molecular compounds composed of?

Two nonmetals.

What is the rule for naming binary molecular compounds?

Name the first element normally and the second element with the suffix “-ide,” using prefixes to indicate number of atoms.

What are the numerical prefixes used in molecular naming?

Mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-.

When is the prefix “mono-” omitted?

When it’s on the first element.

What is a binary acid?

An acid composed of hydrogen and one other nonmetal element.

How are binary acids named?

“Hydro-” + base name of nonmetal + “-ic acid.”

Example: HCl → hydrochloric acid.

What is an oxyacid?

An acid containing hydrogen amd a Polyatomic ion.

How are oxyacids named if the polyatomic ion ends in “-ate”?

Replace “-ate” with “-ic acid.”

Example: HNO₃ → nitric acid.

How are oxyacids named if the polyatomic ion ends in “-ite”?

Replace “-ite” with “-ous acid.”

Example: HNO₂ → nitrous acid.

What distinguishes organic from inorganic compounds?

Organic compounds contain carbon; inorganic generally do not.

What are hydrocarbons?

Compounds containing only hydrogen and carbon.

What are functional groups?

Specific groups of atoms that determine the chemical behavior of organic molecules.

What is an alkane?

Hydrocarbon. Only single C–C and C–H bonds (a saturated hydrocarbon). Nonreactive backbone, nonpolar. CnH2n+2

What is an alkene

Hydrocarbon. A carbon–carbon double bond (C=C). The π bond gives extra reactivity (can undergo addition reactions) CnH2n

What is an alkyne

Hydrocarbon. A carbon–carbon triple bond (C≡C). Has linear geometry and high reactivity (e.g. in additions). CnH2n-2

What is an alcohol (hydroxyl) functional group?

A hydroxyl group (–OH) bonded to carbon (R–OH).

What is an ether functional group?

An oxygen between two carbons (R–O–R').

What is an aldehyde functional group?

A carbonyl bonded to at least one hydrogen (R–CHO).

What is a ketone functional group?

A carbonyl bonded to two carbons (R–CO–R').

What is a carboxylic acid functional group?

A carbonyl bonded to an –OH (–COOH). Acidic (can donate H⁺);

What is an ester functional group?

A carbonyl bonded to an –OR (R–COOR'). Derived from carboxylic acid + alcohol;

What is an amine functional group?

Contains nitrogen bonded to one or more carbons (–NH₂, –NHR, –NR₂).

Prefixes for hydrocarbons

meth-, eth-, prop-, but-, pent-, hex-,hept-,oct-, non-, dec-