NMAT Chem | Bonding

Octet Rule

Atoms are like people trying to complete a team of 8

• Atoms are the happiest with 8 valence electrons

Expanded Octet

Elements in period 3 and others that can hold more than 8 electrons

ex: PCl₅, SF₆ SO₄²⁻

Lewis structure

Chemical symbol of an element surrounded by dots

• usually representing one of the s or p valence electrons of the atom

Formal charge

Tells whether a Lewis structure is the most reasonable arrangement of electrons

Polar bond

Electrons are shared unequally

ex: HF - Fluorine is more electronegative

• electrons would spend more time near fluorine

Nonpolar bond

Electrons are shared equally

ex: H₂

• Same atom with the same pull

Polar molecules

Asymmetrical molecules where the pulls don’t cancel

• You can usually tell from the bent shape

• ex: bent and trigonal pyramidal

Nonpolar molecules

Symmetrical pull from atoms

• The pulls will cancel

• ex: Linear, Tetrahedral, Trigonal planar, Tetrahedral

VSEPR

Shape of CO₂ BF₃ CH₄ NH₃ H₂O

Covalent bond

Each atom contributes one electron

Complex Ion

A central metal ion surrounded by molecules or ions called ligands

Ligands

Atoms that attach to metals

ex: Water, NH₃, Cl^-, CN^-

• All of them have a lone pair of electrons

Coordinate covalent

One atom gives BOTH electrons

• still a covalent bond

• ex: N giving H both bonding electrons

Chelation

Ligands grab the metal they attach to in multiple places; they wrap around it like a claw

ex: Hemoglobin is a large ring-shaped ligand; Vitamin B₁₂ contains a cobalt coordination complex

Intermolecular Forces

Forces between molecules

IMF Strength tier (weakest → strongest)

Dispersion → Dipole-dipole → Hydrogen bond

Dispersion forces

Every molecule has this because electrons are constantly moving

• Like kids running around all the time

• One side becomes slightly negative then positive for short moments; temporary imbalance attracts neighboring molecules → Temporary (instantaneous) dipole

Dipole-Dipole Forces

Only happens with polar molecules

• ex: HF; fluorine pulls harder and if there’s 2 HF molecules, H is attracted to negative F

Hydrogen bonding

Dipole-dipole but on the next tier

• only happens if H is attached to F, O, or N

Why is H₂O special in H bonds?

It’s made up of it

Because of H bonds it has:

• High boiling point

• surface tension

• capillary action

• Ice floating