Coulomb’s Law Chemical Bonding

A. Coulomb’s Law Formula E ∝ Q1Q2 r E= energy of attraction/repulsion between charged particles Q1= charge of first particle Q2=charge of second particle r=distance between particles

A. Coulomb’s Law Formula What it means: The greater the charge… …the greater the attraction of opposite charges …the greater the repulsion of like charges The closer the particles are to each other, the greater the attraction/repulsion Charge beats size just like rock beats scissors! ;-)

B. Ionization Energy I.E.-energy required to remove an electron Stronger attraction between nucleus and electron=harder to remove Q1=charge of an electron Q2=effective nuclear charge Nucleus is shielded by inner electrons Effective nuclear charge increases across a period r=distance Approximate using the period (row)

B. Ionization Energy Why does Na have higher i.e. than K? For K r=4 and for Na r=3, Q1 and Q2 are the same (same column), so… …i.e. is lower for K More shielding/larger size Lower energy means less attraction Easier to remove an electron More metallic (ability to remove e-) This also explains why K is bigger than Na

B. Ionization Energy Na has lower i.e. than Al… Same Q1, same r (energy level) Q2 is 3 for Al and 1 for Na E is higher for Al Greater attraction Holds on to e- more Al is also smaller as greater nuclear charge pulls energy levels in closer

C. Lattice Energy and Bonding E=Lattice Energy: energy required to separate oppositely charged ions Higher lattice energy=stronger bond Q1=charge of first ion Q2=charge of second ion r=bond length: distance between nuclei Can approximate using period of element that is isoelectronic with that ion

C. Lattice Energy and Bonding Isoelec…WHAT?? Isoelectronic—have equal number of electrons Example: Na has 11 electrons in 3 energy levels. When it loses a valence electron it now has 10 electrons in 2 energy levels…just like Neon! Fluorine has 9 electrons in 2 energy levels, it gains one electron and is also isoelectronic with Ne! Also affects size: cations are smaller, anions larger Ion with most protons is smallest

C. Lattice Energy and Bonding

C. Lattice Energy and Bonding Which has a stronger bond: NaCl or KCl? NaCl Na has stronger lattice energy so it has a stronger bond Na+ has electrons in 2 energy levels, which is less than K+ (isoelectronic with Ar, e- in 3 energy levels)

C. Lattice Energy and Bonding Which has a stronger bond: NaCl or AlCl3? AlCl3 Al and Na have same number of energy levels (isoelectronic with Ne) Cl is 1- for both compounds Al has 3+ charge while Na has 1+ charge Greater charge = more attraction

D. Solubility When an ionic compound in water, the ions dissociate Ions are pulled away from each other A compound with a high lattice energy (stronger bond) will be less soluble than a compound with low lattice energy (weaker bond)

D. Solubility Which is more soluble in 80C water: KCl or NaCl? KCl—has lower lattice energy than NaCl Which is more soluble in 80C water: NaCl or AlCl3? NaCl—has lower lattice energy than AlCl3