Pharmaceutical Organic Chemistry I - Lecture 1: Introduction to Organic Chemistry

Flashcards covering introductory organic chemistry concepts from Lecture 1: atomic structure, quantum levels, orbitals, Aufbau/Pauli/Hund rules, octet rule, ionic/covalent/dative bonding, electronegativity, Lewis structures, and lecture review questions.

How is organic chemistry defined in the lecture?

Organic chemistry is the chemistry of compounds that contain the element carbon.

What are the three subatomic particles that make up an atom, and what are their respective electrical charges?

An atom consists of protons (bearing one positive charge, $+1$), electrons (bearing one negative charge, $-1$), and neutrons (which are electrically neutral and bear no charge, $0$).

How do the masses of protons, neutrons, and electrons compare within an atom?

Proton mass and neutron mass are almost identical, whereas electrons have negligible mass.

What is the difference between atomic number ($Z$) and atomic mass ($A$)?

Atomic number ($Z$) is the number of protons (equal to the number of electrons in a neutral atom) and defines the atom's identity. Atomic mass ($A$) is approximated by the mass number, which is the sum of protons plus neutrons in the nucleus.

What formula determines the maximum number of electrons that a principal energy level ($n$) can accommodate?

$2n^2$, meaning the 1st shell ($n=1$) holds up to $2$ electrons, the 2nd shell ($n=2$) holds up to $8$ electrons, and the 3rd shell ($n=3$) holds up to $18$ electrons.

What is an atomic orbital?

An orbital is a region of space within an energy level where electrons are most likely to be found, each characterized by a distinct shape and energy.

Which specific atomic orbitals are depicted along the coordinate axes in this diagram?

The three dumbbell-shaped $2p$ degenerate orbitals: $2p_x$, $2p_y$, and $2p_z$.

What does the Aufbau Principle state, and what does the German word 'Aufbau' mean?

The Aufbau Principle states that electrons fill orbitals starting from the lowest energy level and move step by step upward. The German word 'Aufbau' means 'building up'.

What are degenerate orbitals?

Degenerate orbitals are orbitals that possess the same energy, such as the $2p_x$, $2p_y$, and $2p_z$ orbitals.

What does the Pauli Exclusion Principle dictate regarding electron occupancy in an orbital?

Each orbital can hold a maximum of two electrons, and they must have opposite spins (one clockwise and one anticlockwise).

What is Hund's Rule?

When orbitals of equal energy (degenerate orbitals) are available, electrons fill them one at a time with parallel spins before pairing up, which minimizes electron-electron repulsion.

What is the distinction between valence electrons and core electrons?

Valence electrons are the electrons located in the outermost shell (valence shell) and determine the atom's chemical behavior, while core electrons are in the inner shells and do not participate in chemical bonding.

What is the Octet Rule proposed by G. N. Lewis?

An atom achieves maximum stability if its outer energy level is filled or contains eight electrons; thus, an atom will give up, accept, or share electrons to attain an outer shell with eight electrons.

How does an ionic bond form?

An ionic bond forms through the transfer of one or more electrons from one atom (typically a metal that loses electrons to become a cation) to another (typically a nonmetal that gains electrons to become an anion), creating an electrostatic attraction between the oppositely charged ions.

How does a covalent bond form?

A covalent bond forms when two atoms achieve a filled outer shell by sharing their unpaired valence electrons.

What is electronegativity, and how does it trend across the periodic table?

Electronegativity is the ability of an atom to pull electrons toward itself. It increases across a row from left to right and up a column from bottom to top.

Which element is the most electronegative on the periodic table?

Fluorine ($\text{F}$).

What is the difference between a nonpolar covalent bond and a polar covalent bond?

A nonpolar covalent bond occurs when bonding electrons are shared equally between atoms with identical electronegativity (such as $\text{F}-\text{F}$, $\text{C}-\text{C}$, or $\text{C}-\text{H}$), whereas a polar covalent bond occurs when electrons are shared unequally between atoms of different electronegativities, producing partial positive ($\delta^+$) and partial negative ($\delta^-$) charges.

What fundamental rule governs the reactivity of organic compounds?

Electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules.

What is a coordinate bond (dative covalent bond)?

A coordinate bond is a covalent bond in which both shared electrons come entirely from the same donor atom possessing a lone pair, which donates them into an empty orbital of an electron-deficient acceptor atom.

What type of chemical bond is formed in the reaction illustrated below?

A coordinate covalent (dative) bond, where the nitrogen atom of $\text{NH}_3$ donates its lone pair of electrons to the electron-deficient boron atom of $\text{BF}_3$.

What distinguishes a 'Full Lewis' structure from a 'Half-Lewis' structure?

In a Full Lewis structure, both bonding electron pairs and lone pairs are represented exclusively as pairs of dots, whereas in a Half-Lewis structure, covalent bonds are depicted as solid dashes (lines) and nonbonding lone pairs remain as pairs of dots.

If the atomic number $Z$ of sulfur ($\text{S}$) is $16$, how many valence electrons does it have?

$6$ valence electrons (electron configuration: $1s^2\,2s^2\,2p^6\,3s^2\,3p^4$; outermost shell $n=3$ contains $2 + 4 = 6$ electrons).

If the atomic number $Z$ of magnesium ($\text{Mg}$) is $12$, how many valence electrons does it have?

$2$ valence electrons (electron configuration: $1s^2\,2s^2\,2p^6\,3s^2$; outermost shell $n=3$ contains $2$ electrons).

How are $\text{NaCl}$, $\text{CH}_4$, and $\text{HCl}$ correctly ranked in order from most polar to least polar?

$\text{NaCl} > \text{HCl} > \text{CH}_4$ (ionic bond is most polar, polar covalent $\text{HCl}$ is intermediate, nonpolar covalent $\text{CH}_4$ is least polar).

Among $\text{CH}_2=\text{CH}_2$, $\text{Cl}_2$, $\text{H}_3\text{C}-\text{CH}_3$, and $\text{NH}_3$, which molecule does NOT contain a nonpolar covalent bond?

$\text{NH}_3$ (ammonia contains polar covalent $\text{N}-\text{H}$ bonds due to the difference in electronegativity between nitrogen and hydrogen).