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Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular geometry. The basic idea: electron pairs repel each other and arrange themselves to minimize repulsion.

When you toggle "Angles" on a molecule, you see the actual bond angles. These angles are determined by:

• 1.The number of bonding pairs (atoms attached to central atom)
• 2.The number of lone pairs (non-bonding electrons)

Lone pairs are pairs of valence electrons that don't participate in bonding. They're shown as purple lobes when you toggle "Lone Pairs" on.

Though invisible in a simple molecular formula, lone pairs have profound effects:

• They reduce bond angles by taking up more space than bonding pairs
• They can act as nucleophiles in reactions (donating electrons)
• They determine the molecule's polarity and reactivity

A molecule is polar if it has an uneven distribution of electron density, creating a net dipole moment. Determining polarity requires two steps:

1. 1.Are the bonds polar? Compare electronegativities. A difference > ~0.4 means the bond is polar (e.g., O-H has ΔEN = 1.24).
2. 2.Does the geometry cancel the dipoles? Symmetric shapes like linear (CO₂) and tetrahedral (CH₄) cancel polar bonds. Asymmetric shapes like bent (H₂O) leave a net dipole.

Polarity determines key physical properties: polar molecules have higher boiling points, dissolve in water (like dissolves like), and interact through dipole-dipole forces and hydrogen bonding.

Intermolecular forces (IMFs) are attractions between molecules, not the covalent bonds within them. They determine boiling point, solubility, viscosity, and whether a substance is a solid, liquid, or gas at room temperature.

There are three main types, listed from weakest to strongest:

1. 1.London Dispersion Forces (LDF) are present in all molecules. Caused by temporary fluctuations in electron density. Stronger for larger, more polarizable molecules.
2. 2.Dipole-Dipole Forces occur only in polar molecules. The δ+ end of one molecule attracts the δ− end of another.
3. 3.Hydrogen Bonding is a strong type of dipole-dipole force. Requires H bonded to N, O, or F (donor) and a lone pair on N, O, or F (acceptor).

Forces are additive: a molecule that can hydrogen bond also has dipole-dipole and London dispersion forces. The strongest force present dominates the molecule's physical properties.

The periodic table isn't just a list of elements. It's organized so that properties change predictably across rows (periods) and down columns (groups). These patterns arise from how electron shells fill and how the nucleus pulls on valence electrons.

Two forces compete: effective nuclear charge (Z_eff) increases across a period as protons are added while electrons go into the same shell, pulling electrons closer. Meanwhile, adding a new shell down a group increases shielding, pushing valence electrons farther from the nucleus.

Understanding these two forces explains all four major trends: electronegativity, atomic radius, ionization energy, and electron affinity.

Every organic molecule needs a unique, systematic name so chemists worldwide can communicate precisely. The IUPAC naming system (International Union of Pure and Applied Chemistry) provides a set of rules that map any structure to one unambiguous name.

Common names like "isobutane" or "neopentane" are still used informally, but they don't scale to the millions of known organic compounds. IUPAC names are constructed from the structure itself, so you can go from name to structure (and back) once you know the rules.

For simple alkanes, naming follows four steps: find the longest carbon chain, number it correctly, name the substituents, and assemble the final name alphabetically.

A molecule is chiral if it cannot be superimposed on its mirror image, like your left and right hands. Chirality most commonly arises at a carbon bonded to four different groups, called a stereocenter.

The two mirror-image forms are called enantiomers. They share the same physical properties but interact differently with other chiral molecules, which is why chirality matters in biology and medicine.

Chemists assign each stereocenter an R or S configuration using the Cahn-Ingold-Prelog (CIP) priority rules, based on the atomic numbers of the attached groups.