Bonding and substitution

What is the difference between ionic and covalent bonding?

Ionic bonding involves electron transfer; covalent bonding involves electron sharing.

What controls whether a bond is ionic or covalent?

The electronegativity difference between the atoms.

What is electronegativity?

The tendency of an atom to attract electrons in a bond.

Why does electronegativity increase across a period?

Increasing nuclear charge pulls electrons more strongly.

What is coordination number?

The number of nearest neighboring ions around a central ion.

What determines coordination number?

The cation-to-anion radius ratio.

What is Pauling’s first rule?

Coordination number is controlled by the radius ratio.

What is Pauling’s third rule?

Polyhedra avoid sharing edges and faces to reduce repulsion.

What is a solid solution?

Continuous chemical substitution between ions in a mineral structure.

What two factors control substitution in minerals?

Ionic radius and ionic charge.

What is coupled substitution?

Two ions substitute together to maintain charge balance.

Why do albite and anorthite form a solid solution?

Na⁺ ↔ Ca²⁺ substitution is balanced by Al–Si substitution.

Why do anorthite and orthoclase NOT form a solid solution?

K⁺ is too large compared to Ca²⁺, causing structural strain.