Covalent Bonding & Molecular Shapes

Vocabulary flashcards covering key concepts from covalent bonding, Lewis structures, and VSEPR-based molecular shapes.

Molecules

Two or more atoms held together by covalent bonds; the basic unit of many substances.

Lewis dot diagrams (Lewis structures)

A schematic representation of valence electrons around atoms using dots; shows bonding and lone pairs.

VSEPR theory

Valence Shell Electron Pair Repulsion theory; predicts molecular shapes by minimizing repulsion between electron pairs.

Octet rule

Atoms tend to have eight electrons in their valence shell; exceptions occur (e.g., Be, B; expanded octets possible for some elements).

Expanded octet

Central atoms, especially period 3 and beyond, can have more than eight electrons around them.

Central atom

The atom at the center of a Lewis structure around which other atoms are arranged.

Lone pair

A non-bonding pair of electrons on an atom.

Bonding pair

A pair of electrons shared between two atoms in a covalent bond.

ANS method

Available, Needed, Shared method used to determine the number of bonds in molecules with more than two atoms.

Available electrons

Valence electrons that can be used for bonding.

Needed electrons

Valence electrons required to complete each atom’s valence shell.

Shared electrons

Electrons counted toward both atoms in a covalent bond.

Bond

A shared pair of electrons linking two atoms.

Non-polar covalent bond

A covalent bond in which electrons are shared evenly between two atoms.

Polar covalent bond

A covalent bond in which electrons are shared unequally, creating partial charges.

Ionic bond

Electrostatic attraction between oppositely charged ions.

Non-polar covalent substance

Substance composed mainly of non-polar covalent bonds; typically low polarity and low melting/boiling points.

Polar covalent substance

Substance with polar covalent bonds; generally soluble in polar solvents and has higher solubility than non-polar substances.

Giant covalent substance

Network solids with covalent bonds throughout the lattice (e.g., diamond); very high melting/boiling points and insoluble.

Solubility in polar solvents

Degree to which a substance dissolves in polar solvents; higher for polar substances.

Solubility in non-polar solvents

Degree to which a substance dissolves in non-polar solvents; higher for non-polar substances.

Electrical conductivity

Ability to conduct electricity; covalent solids are typically poor conductors; graphite/graphene can conduct under certain conditions.

Bonding pairs vs lone pairs

Bonding pairs form covalent bonds; lone pairs are non-bonding electron pairs on atoms.

Shapes of molecules

Geometries predicted by VSEPR based on the arrangement of electron pairs around the central atom.

Linear geometry

Molecule with two regions of electron density; atoms lie in a straight line (example: CO2).

Bent (V-shaped)

Molecule with three or more regions of electron density but two bonding regions; presence of lone pairs bends the shape.

Trigonal planar

Three regions of electron density, all bonding; planar triangular arrangement.

Tetrahedral

Four regions of electron density, all bonding; bond angles about 109.5°.

Trigonal pyramidal

Four regions of electron density with one lone pair; three bonds; shape like a pyramid (e.g., NH3).

Trigonal bipyramidal

Five regions of electron density; can involve expanded octet; axial and equatorial positions.

Octahedral

Six regions of electron density; geometry based on an octahedron; may involve expanded octet.

Carbon central atom rule

When carbon is present in a molecule, it is typically placed at the center in Lewis structures.

H2O Lewis structure

Water: oxygen is the central atom with two bonds to hydrogens and two lone pairs on O.

CH2O Lewis structure

Formaldehyde example: central carbon with bonds to two hydrogens and one oxygen (often with a double bond to O).