Bonding

Types

Ionic

metal + non-metal

• hard, brittle solids
• high melting points
• solution conducts electricity

Covalent

non-metal + non-metal

• lower melting and boiling points
• solution doesn't conduct electricity (except it is acid or base, it reacts with water and produces salts, which conducts electricity when dissolved)
• Larger molecules -> stronger intermolecular force -> higher melting point -> solid at room temperature

Network covalent materials

• hard, resilient solid
• very high melting point

e.g. diamond

Metallic

metal + metal

• solid, often with high melting points
• shiny, silver-colored
• conduct electricity
• malleable

Lewis Structures

1. Sum all valence electrons
2. Draw skeletal structure
   • Only use single bonds
   • Atom with least electronegativity is usually at the center
3. Use the remaining electrons to form octets, from the most electronegative to the least.
   • metals > row 3 can have more than an octet
4. If there is an atom remaining without an octet, create a double / triple bond.
   • Exceptions: Be, B or Al (or atoms in g2 and g3) don't need an octet
5. If there are an odd number of electrons, the least electronegative atom has less than eight electrons in its valence shell.

Formal Charge

formal charge = valence electrons an atom should have - it actually have

A lewis strucutre with formal charge closest to 0 is the most possible lewis strucutre.

Resonance

When multiple lewis structures are equally likely, the actual structure is the "average" of all possible lewis structures.

Average bond order: average of the order of the same bond across all possible structures. e.g. For the bottom O-N bond, average bond order = (1+2+1)/3 = $\frac{4}{3}$

Average formal charge: average of the formal charge of the same atom across all possible structures. e.g. For the bottom Oxygen atom, average formal charge = (-1 + 0 + -1)/3 = $-\frac{2}{3}$​

VSEPR theory

Electron pairs and bonds repel each other, electron pairs repel more.

Polarity

1. Calculate the polarity of bonds based on electronegativity

2. Treat polarity of bonds as vectors and sum them to get the polarity of the molecule

3. $\delta-$: slightly negatively charged

4. $\delta+$: slightly positively charged

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Last update: October 3, 2021
Created: September 19, 2021