ACER 9/28 Lecture #9: Ionic Bonding

What does isoelectronic mean?

having the same total number of electrons or the same electronic structure

How do you remove electrons when making an ion?

Remove electrons from the outermost orbital first. Follow Hund’s rule.

Ionic Bonds

occur when charged species—anions and cations formed from the transfer of electrons between atoms—interact through electrostatic (aka Coulombic) forces

results in a bonded-atom pair is lower in energy than the separate atoms

Covalent bonds

occur when atoms “share” electrons

results in a bonded-atom pair is lower in energy than the separate atoms

Describe a Potential Energy Curve (Potential Energy Diagram).

Discuss “vibration” and the lowest point.

A PED shows bond length and potential energy. y-axis is potential energy, the stored energy between atoms. x-axis is internuclear distance, the space between the centers of two atoms.

The curve line is the electronic energy level. The black lines correspond to vibrational energy levels.

The lowest point, the zero-point energy (ZPE), shows the optimal bond length and the lowest possible potential energy (v₀) of the bonded pair. It also shows the bond energy, how much energy is needed to break the bond.

Why is the zero-point energy in the middle of the potential energy diagram?

To the left, the atoms are too close together and are pushed apart due to nuclei-repulsion and overlapping electron clouds. Potential energy increases towards infinity.

To the right, the atoms are too far apart and their attractive forces decrease to zero. The atoms separate.

How do vibrational energy levels explain fluorescence?

Fluorescence requires not just a single atom but a bond with vibrational energy. Those vibration energies allow a molecule to lose some energy as heat before emitting a lower-energy photon.

Which groups on the periodic table belong to the s-block, p-block, and d-block?

s-block: Groups 1-2

p-block: Groups 13-18

d-block: Groups 3-12

Compare how elements in each subshell-block of the periodic table fill their octets as well as exceptions.

s-block elements form cations by losing their s-electrons.

d-block elements (most of which are transition metals) also lose their s-electrons and then a variable number of d-electrons.

• Only Group 12 loses their s-electrons and no d-electrons, except for mercury Hg which loses d-electrons in rare cases.

p-block elements share their outer s- and p-electrons. They usually don’t lose electrons but rather share or gain electrons.

• Non metals gain—and rarely lose—electrons due to high ionization and electron affinity energies. The exception is Hydrogen, a non-metal in the s-group which easily loses an electron.

What is variable valency and where does it apply.

It is the ability to form various oxidation states.

It applies mainly to transition metals due to the small difference in energy between their outermost s-electrons and d-electrons.

How will a group 4 element form an octet?

Generally by losing 4 electrons.

Theoretically they could also gain 4 electrons but that is less common and more challenging energy-wise.

What are binary ionic compounds? How do they form?

Compounds formed with just two ions, usually between an s-block metal and a non-metal

They form ionic crystalline solids where a large number of oppositely charged ions bond quickly and release large amounts of energy.

• For example, NaCl. The ionization energy of sodium and the electron affinity of chlorine is not a favorable process on its own. However, when the stabilization energy from the crystal lattice is added, the overall process is very favorable (total change in energy is very negative).

Identify and explain the properties of ionic solids.

Ionic solids have high melting points due to the high energy needed to separate the ions.

They are brittle because a physical force can easily shift the layers of ionic crystal and cause ions with like-charges to align and repel each other.