O Chem 1-Chap 1

What is organic chemistry?

The study of carbon-containing compounds and their structure, bonding, and reactions.

Why is carbon central to organic chemistry?

Carbon forms four stable covalent bonds and can make chains and rings.

What particles are found in the nucleus?

Protons and neutrons.

What determines an element’s identity?

Number of protons (atomic number).

What are isotopes?

Atoms of the same element with different numbers of neutrons.

What determines chemical behavior?

Valence (outer-shell) electrons.

What is an s orbital?

Spherical orbital; lower energy.

What is a p orbital?

Dumbbell-shaped orbital; higher energy.

Which orbitals are used by second-row elements?

2s and 2p orbitals.

Why do atoms form bonds?

To reach a more stable electron configuration.

What is a covalent bond?

Sharing of electrons between atoms.

What is an ionic bond?

Transfer of electrons creating charged ions.

How many bonds does hydrogen form?

1 bond.

How many bonds does carbon form?

4 bonds.

How many bonds does nitrogen form?

3 bonds and 1 lone pair.

How many bonds does oxygen form?

2 bonds and 2 lone pairs.

How many bonds do halogens form?

1 bond and 3 lone pairs.

What do Lewis structures show?

Valence electrons as bonds and lone pairs.

What is the octet rule?

Second-row elements are most stable with 8 valence electrons.

Which element is an exception to the octet rule?

Hydrogen (only needs 2 electrons).

Steps to draw a Lewis structure (order)?

Arrange atoms → count electrons → form bonds → add lone pairs → check octets → check formal charges.

Formal charge formula

Valence e⁻ − (lone pair e⁻ + ½ bonding e⁻)
Valence e^- - sticks- dots

Why is formal charge important?

Helps identify the most stable Lewis structure.

Preferred formal charge arrangement

Fewest charges; negative charge on more electronegative atom.

What are isomers?

Compounds with the same molecular formula but different structures.

What are constitutional isomers?

Isomers with different atom connectivity.

Which elements can have expanded octets?

Third-row and beyond (P, S).

Which elements can have incomplete octets?

Boron, beryllium.

What is resonance?

Multiple valid Lewis structures for the same molecule.

What changes in resonance structures?

Electron placement only (not atom positions).

What is the real structure called?

Resonance hybrid.

Does resonance mean structures flip back and forth?

No.

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion.

Geometry with 2 electron groups

Linear (180°).

Geometry with 3 electron groups

Trigonal planar (120°).

Geometry with 4 electron groups

Tetrahedral (109.5°).

What counts as an electron group?

Bonds and lone pairs.

Effect of lone pairs on bond angles

They compress angles.

How does bond length change across a period?

Decreases.

How does bond length change down a group?

Increases.