Organic and Nuclear Chemistry

Organic Chemistry: The Chemistry of Carbon

Organic chemistry is the study of compounds containing carbon. Carbon is unique because it forms four covalent bonds and can chain into long structures, rings, and branches, giving millions of compounds. The simplest organic compounds are hydrocarbons, made only of carbon and hydrogen.

A homologous series is a family of organic compounds that share a general formula and differ from the next member by one -CH2- unit. Members of a series have similar chemical properties and a gradual trend in physical properties like boiling point.

Hydrocarbon Series (Organic Hydrocarbons table, legacy Table Q)

The 2025 NYS Chemistry Reference Tables include the Hydrocarbons section (the section the legacy edition labeled Table Q), which gives the general formulas of the three hydrocarbon series:

A saturated hydrocarbon (alkane) contains only single carbon-carbon bonds and holds the maximum number of hydrogen atoms. An unsaturated hydrocarbon (alkene or alkyne) contains at least one double or triple bond and therefore fewer hydrogens. For example, ethane (C2H6) is a saturated alkane, ethene (C2H4) is an alkene, and ethyne (C2H2) is an alkyne.

Worked Formula Example

A hydrocarbon has 4 carbons and a single double bond. It is an alkene, so use CnH2n with n = 4: C4H8 (butene). If it were the alkane (butane), it would be C4H10 using CnH2n+2.

Functional Groups (Organic Functional Groups table, legacy Table R)

The Organic Functional Groups section (the section the legacy edition labeled Table R) lists functional groups — the reactive atom clusters that define an organic family and control its reactions. Key groups to recognize:

• Alcohols contain the -OH (hydroxyl) group, as in methanol CH3OH.
• Organic acids contain the -COOH (carboxyl) group, as in acetic acid.
• Halides contain a halogen (F, Cl, Br, I) bonded to carbon.
• Amines contain nitrogen; esters and ethers contain characteristic oxygen linkages.

A Regents item may show a structure and ask you to name the family by matching the functional group to the Organic Functional Groups table (legacy Table R). Note that an alcohol's -OH does NOT make it a base — it is covalently bonded and does not release OH- ions in water.

Nuclear Chemistry: Radioactive Decay

Nuclear chemistry deals with changes in the nucleus. An unstable nucleus is radioactive and emits particles or energy to become more stable. Three decay types appear on the Regents:

• Alpha (α) decay emits an alpha particle, a helium nucleus with mass number 4 and charge +2. The parent loses 4 mass and 2 protons.
• Beta (β) decay emits a beta particle (a high-speed electron) with mass 0 and charge -1; a neutron converts to a proton, so the atomic number increases by 1.
• Gamma (γ) radiation is pure high-energy electromagnetic radiation with no mass or charge; it changes neither mass number nor atomic number.

Balancing Nuclear Equations

In a nuclear equation, two quantities are conserved: the sum of mass numbers (top) and the sum of atomic numbers (bottom) must be equal on both sides. Solve for an unknown by making each side balance.

Worked Nuclear Example

Uranium-238 (mass 238, atomic number 92) undergoes alpha decay. The alpha particle is mass 4, charge 2. The product has mass 238 - 4 = 234 and atomic number 92 - 2 = 90, which is thorium-234. Mass numbers (238 = 234 + 4) and atomic numbers (92 = 90 + 2) both balance.

Half-Life Calculations

The half-life is the time required for half of a radioactive sample to decay. The Selected Radioisotopes table (the section the legacy edition labeled Table N) lists each radioisotope's half-life. After n half-lives, the fraction remaining is (1/2)^n.

Worked Half-Life Example

A 40.0-gram sample of a radioisotope has a half-life of 5 years. After 15 years, that is 15 / 5 = 3 half-lives. Remaining fraction = (1/2)^3 = 1/8. So 40.0 x 1/8 = 5.0 grams remain.

Naming and Drawing Organic Structures

The Regents may ask you to name a hydrocarbon or draw its structural formula. The first part of a name comes from the carbon count: meth- (1), eth- (2), prop- (3), but- (4), pent- (5). The ending tells the series: -ane (alkane), -ene (alkene), -yne (alkyne). So propane has 3 carbons and only single bonds, while propene has 3 carbons and one double bond.

Isomers are compounds with the same molecular formula but different structures. For example, butane and methylpropane both are C4H10, yet their atoms connect differently, giving slightly different properties. Recognizing isomers is a common 1-credit item.

Fission, Fusion, and Beneficial Uses

Two large-scale nuclear processes appear in sustainability clusters. Fission splits a large nucleus (such as uranium-235) into smaller nuclei, releasing energy used in nuclear power plants. Fusion combines small nuclei (such as hydrogen isotopes) into a larger one, the energy source of the Sun. Both release enormous energy because a small amount of mass converts to energy.

Radioisotopes also have beneficial uses tested on the exam: carbon-14 dating estimates the age of once-living material from its known half-life, and certain isotopes serve as medical tracers or cancer treatments. Connecting a half-life value from the Selected Radioisotopes table (legacy Table N) to a real application is exactly the kind of reasoning the new exam rewards.

Common Mistakes

• Using the alkane formula for an alkene or alkyne — always check the bonding first.
• Calling an alcohol a base because it has -OH; it does not ionize.
• Forgetting that beta decay RAISES atomic number by 1 (a neutron becomes a proton).
• Adding mass numbers but forgetting to balance atomic numbers in nuclear equations.
• Confusing half-life count: 15 years at a 5-year half-life is 3 half-lives, not 15.