ORT Chemistry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mass number

The sum of protons and neutrons in a nucleus. Isotopes of an element share the same atomic number but differ in mass number because their neutron counts differ.

Hund's rule

Electrons occupy degenerate orbitals singly with parallel spins before any pairing occurs. This minimizes repulsion and explains the paramagnetism of atoms with unpaired electrons.

Effective nuclear charge

The net positive charge experienced by an outer electron after inner electrons shield the nucleus. It increases across a period, shrinking atomic radius and raising ionization energy.

VSEPR theory

Electron pairs around a central atom arrange to minimize repulsion. Lone pairs repel more strongly than bonding pairs, so CH4 is 109.5 degrees while water is about 104.5 degrees.

Bond order

Half the difference between bonding and antibonding electrons in molecular orbital theory. Higher bond order means a shorter, stronger bond, as in N2 with order three.

Hydrogen bond

An attraction between a hydrogen bonded to N, O, or F and a lone pair on a nearby electronegative atom. It raises boiling points and solubility in water.

Amphoteric oxide

An oxide that reacts with both acids and bases, such as Al2O3 and ZnO. It dissolves in strong alkali to form aluminates or zincates and in acid to form salts.

Disproportionation

A redox reaction in which one element in a single substance is simultaneously oxidized and reduced. Chlorine in cold dilute alkali gives chloride and hypochlorite.

Transition metal color

Color arises from d-d electronic transitions when partially filled d orbitals split in a ligand field. Ions with d0 or d10 configurations, such as Zn2+, are colorless.

Limiting reagent

The reactant consumed first, which determines the maximum product. Divide each reactant's moles by its coefficient; the smallest quotient identifies it.

Molar volume

The volume occupied by one mole of gas, about 22.4 liters at standard temperature and pressure. It converts gas volume to moles in stoichiometric calculations.

Le Chatelier's principle

When a system at equilibrium is disturbed by concentration, pressure, or temperature change, it shifts to oppose the disturbance. Catalysts do not shift the position of equilibrium.

Solubility product

The equilibrium constant for dissolving a sparingly soluble salt, written as the product of ion concentrations raised to stoichiometric powers. Precipitation occurs when the ion product exceeds it.

Buffer solution

A mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid, that resists pH change. Its pH follows pH = pKa + log(base/acid).

van't Hoff factor

The number of particles one formula unit produces in solution, used to correct colligative property calculations. It is about 2 for NaCl and 3 for CaCl2.

Oxidation number

A bookkeeping charge assigned to an atom assuming bonds are ionic. Free elements are zero, oxygen is usually minus two, and the sum equals the species charge.

Standard cell potential

The difference between cathode and anode standard reduction potentials. A positive value indicates a spontaneous galvanic reaction and relates to free energy by delta G = minus nFE.

Nernst equation

It corrects cell potential for nonstandard concentrations: E = E standard minus (0.0592/n) log Q at 25 degrees Celsius. It predicts how ion concentration shifts voltage.

Markovnikov's rule

In addition of HX to an alkene, the hydrogen adds to the carbon bearing more hydrogens, giving the more stable carbocation intermediate and the more substituted product.

Tollens' test

Ammoniacal silver nitrate oxidizes aldehydes to carboxylates, depositing metallic silver as a mirror. Ketones give no reaction, so it distinguishes the two carbonyl types.

Aromaticity

A cyclic, planar, fully conjugated system with 4n+2 pi electrons is aromatic and unusually stable. Benzene undergoes substitution rather than addition to preserve this stability.

SN2 mechanism

A one-step nucleophilic substitution with backside attack, giving inversion of configuration. Rate depends on both substrate and nucleophile, favoring methyl or primary halides.

Carbocation

A positively charged carbon intermediate with an incomplete octet. Stability increases from methyl to primary to secondary to tertiary, guiding SN1 and elimination product ratios.

Grignard reagent

An organomagnesium halide (RMgX) formed from alkyl halide and magnesium in dry ether. It adds to carbonyls to give alcohols and reacts with water, so anhydrous conditions are required.

Condensation polymerization

Monomers join with loss of a small molecule such as water or HCl, forming polyesters and polyamides. Unlike addition polymerization, the repeat unit lacks all original monomer atoms.

Peptide bond

An amide linkage formed between the carboxyl group of one amino acid and the amino group of another, releasing water. Repeating peptide bonds form the protein backbone.

Reducing sugar

A sugar with a free aldehyde or ketone group that reduces Tollens' or Fehling's reagent. Glucose and maltose are reducing; sucrose is not.

Flame test colors

Characteristic emission colors identify metal ions: sodium yellow, potassium lilac, calcium brick-red, barium yellow-green, copper blue-green, lithium crimson.

Sulfate ion test

Adding barium chloride to an acidified sample gives a white precipitate of barium sulfate that is insoluble in dilute acid, confirming sulfate.

Titration endpoint

The point where the indicator changes color, ideally matching the equivalence point. Add titrant dropwise near the end and read the burette at eye level.

Diluting concentrated acid

Add acid slowly to water with stirring, never water to acid. The highly exothermic hydration can cause boiling and spattering if the order is reversed.

Ammonium ion test

Warming the sample with sodium hydroxide releases ammonia gas, which turns moist red litmus paper blue and has a pungent smell.