Basic Chemistry - Unit 4: Chemical Bonding (Video Notes)

A set of vocabulary-style flashcards covering key terms and concepts from the Basic Chemistry - Unit 4: Chemical Bonding lecture notes.

Electronic theory of valency (Kossel and Lewis)

Idea that valency is determined by electrons in the outer shell; Lewis structures illustrate valence electrons.

Valency

The combining power of an atom; number of bonds it tends to form; can be described as positive (electrovalency) or negative.

Chemical bond

The force that holds two or more atoms together in a compound.

Ionic bond

Electrostatic attraction between oppositely charged ions in an ionic compound.

Covalent bond

Sharing of electrons between atoms to achieve a stable outer shell.

Coordinate (dative) bond

A covalent bond formed when both electrons are donated by one atom (donor with lone pair) to another.

Polar covalent bond

Covalent bond with unequal sharing of electrons due to electronegativity difference.

Dotted line representation

A diagrammatic way to show a covalent bond (shared electron pair) between atoms.

Delocalised electrons

Electrons not bound to a single atom; move freely, enabling electrical conductivity in metals.

Metallic bond

Bonding in metals arising from a 'sea' of delocalized electrons shared by a lattice of positive ions.

Ionic solid

A solid composed of ions held together by ionic bonds; high melting point; conducts when molten or dissolved.

Covalent solid (network solid)

A solid in which atoms are connected by covalent bonds forming a network (e.g., diamond).

Simple cubic unit cell (SC)

Unit cell with one atom at each corner; 1 atom per cell; CN = 6; relatively low packing efficiency.

Body-centered cubic unit cell (BCC)

Unit cell with an atom at each corner and one in the center; 2 atoms per cell; CN = 8.

Face-centered cubic unit cell (FCC)

Unit cell with atoms at corners and at the centers of all faces; 4 atoms per cell; CN = 12; high packing efficiency.

Hexagonal close-packed (HCP) structure

A close-packed structure with ABAB stacking and CN = 12; common in metals like Zn and Mg.

Coordination number

The number of nearest-neighbour atoms surrounding a given atom in a crystal.

Bravais lattice

One of 14 possible lattice types that describe the periodic arrangement of points in a crystal.

Crystal system

Seven lattice systems (cubic, tetragonal, orthorhombic, rhombohedral, hexagonal, monoclinic, triclinic).

Lattice point

The position in a crystal lattice where an atom, ion, or molecule is represented.

Unit cell

The smallest repeating unit of a crystal that can generate the entire lattice by translation.

Crystal site

A position in a crystal lattice occupied by an atom or ion.

Lattice vs. Bravais lattice

Bravais lattice is a mathematical description of the periodic arrangement; a lattice point represents that arrangement.

Anisotropic

Properties that vary with direction within a material.

Isotropic

Properties that are the same in all directions.

Ionic solid properties

High melting point; poor conductivity in solid state; conducts when molten or dissolved; often soluble in polar solvents.

Polar molecular solid

A solid composed of polar molecules held together by dipole-dipole interactions or hydrogen bonding.

London dispersion forces

Weak intermolecular forces arising from temporary dipoles; present in all molecules, stronger in larger/more polarizable atoms.

Hydrogen bond

Strong dipole-dipole interaction involving hydrogen attached to N, O, or F; highly directional.

Graphite conductivity

Good electrical conductivity due to delocalised electrons within layered planes.

Diamond structure

Covalent network solid where each carbon is bonded to four others.

Number of atoms per SC unit cell

One atom per unit cell (via corner counting).

Number of atoms per BCC unit cell

Two atoms per unit cell (corners plus center).

Number of atoms per FCC unit cell

Four atoms per unit cell (corner and face-centered atoms).

Coordination number for SC

6 nearest neighbours.

Coordination number for BCC

8 nearest neighbours.

Coordination number for FCC/HCP

12 nearest neighbours.

Which crystal structure has 4 atoms per cell?

FCC (Face-Centered Cubic) has 4 atoms per unit cell.

Which crystal structure has CN = 12?

FCC and HCP both have coordination number 12.

Which crystal system has a = b, a = 90°, γ = 120°?

Hexagonal crystal system.

Which crystal system has a = b = c and all angles 90°?

Cubic crystal system.

Which crystal form has atoms at corners and face centers?

FCC (face-centered cubic) structure.

Which metal shows HCP packing?

Zn (and Mg, Ti)—examples of hexagonal close-packed metals.

The ability of metals to be drawn into wires is called

Ductility.

The ability of a metal to be hammered or rolled into sheets is called

Malleability.

Elasticity

Ability of a material to return to its original shape after removing stress.

Tensile strength

Resistance to being pulled apart.

Homogeneous catalysis

Catalysis where reactants and catalyst are in the same phase.

Heterogeneous catalysis

Catalysis where reactants and catalyst are in different phases.

Electrovalency of oxygen in MgO

-2 (oxygen typically carries a -2 electrovalency in MgO).

Bond formed between two electronegative atoms

Covalent bond.

False statement about metallic bonds

Electrons are highly localized (false; electrons in metallic bonds are delocalized).

Which type of crystalline solid is CO2 (solid)?

Molecular solid (solid CO2 is dry ice, held by intermolecular forces).

In coordinate bond, the donor atom is

Rich in lone pairs (donor supplies electron pair).

Coordination number refers to

Number of nearest neighbours around an atom in a crystal.

Which property of water is due to hydrogen bonding?

High boiling point compared with similar non-hydrogen-bonded molecules.

The Bravais lattice concept states there are

14 distinct Bravais lattices.

Which sequence describes cubic close packing?

ABCABC stacking sequence.

In BCC, how many atoms per unit cell?

Two atoms per cell.

Which solid is malleable and ductile?

Metallic solid.

Which type of solid is diamond?

Covalent (network) solid.

What is the packing efficiency of simple cubic packing?

About 52% (lower than BCC, FCC/HCP).