Trends in Atomic Structure and Bonding Concepts

Atomic radius trend down a group

Increases (atoms get bigger)

Atomic radius trend across a period

Decreases (atoms get smaller)

Ionization energy trend down a group

Decreases (easier to remove electrons)

Ionization energy trend across a period

Increases (harder to remove electrons)

Effective nuclear charge (Z_eff) across a period

Increases (more protons pulling electrons)

Effective nuclear charge down a group

Decreases (shielding increases)

Which has the largest atomic radius?

Rb

Which has the highest ionization energy?

Argon (Ar)

Bond between metal and nonmetal

Ionic bond

Bond between two nonmetals

Covalent bond

Electrons are transferred in what bond?

Ionic bond

Electrons are shared in what bond?

Covalent bond

What is lattice energy?

Energy to separate one mole of an ionic solid into gas-phase ions

Factors that increase lattice energy

Smaller ions and higher charges

Which has greater lattice energy: MgCl₂ or KCl?

MgCl₂

Example of ionic compound

NaCl

Example of covalent compound

CO₂

Definition of atomic radius

Distance from nucleus to outermost electron

Definition of ionization energy

Energy needed to remove an electron

Definition of lattice energy

Energy required to break apart an ionic solid

What rule is used to draw stable Lewis structures?

Octet Rule (most atoms want 8 valence electrons)

Can atoms be moved when converting resonance structures?

No, only electrons can be moved

Which molecule violates the octet rule?

SeF₄

What are delocalized electrons?

Electrons shared across more than two atoms (resonance)

Which molecules show delocalized bonding?

NO₂⁻ and H₂CO

What is hybridization of carbon in CH₄?

sp³

What is hybridization of carbon in CH₂=CH₂ (ethylene)?

sp²

Hybridization for linear geometry

sp

Hybridization for trigonal planar geometry

sp²

Hybridization for tetrahedral geometry

sp³

Hybridization for trigonal bipyramidal geometry

sp³d

Hybridization for octahedral geometry

sp³d²

Where do lone pairs go in trigonal bipyramidal geometry?

Equatorial positions (less repulsion)

Bond formed by head-on orbital overlap

Sigma (σ) bond

Bond formed by side-on overlap of p orbitals

Pi (π) bond

What is molecular orbital theory used for?

To explain bonding using atomic orbitals combining into molecular orbitals

Bond order formula

(Bonding electrons - Antibonding electrons) ÷ 2

Bond order of CN⁻

3

Is CN⁻ paramagnetic?

No (all electrons are paired)

How many σ and π bonds in CH₃COCH₃ (acetone)?

9 σ bonds, 1 π bond

Bond energy definition

Energy needed to break a chemical bond

ΔH (reaction enthalpy) formula using bonds

ΔH = Bonds broken - Bonds formed

What is the ΔH for CH₄ + 2O₂ → CO₂ + 2H₂O?

-802 kJ/mol

Most polar covalent bond (of H, C, N, O)?

O-H

Dipole moment formula

μ = 4.77 × bond length (Å) for 100% ionic

How to find percent ionic character

(Measured μ / Calculated μ) × 100

Percent ionic character of LiBr

70.2%

What causes polarity in a molecule?

Uneven distribution of electrons and asymmetrical shape

Is a molecule with symmetric polar bonds polar?

No (polarity cancels out)

What are London dispersion forces?

Temporary attractions due to random electron movement

What are dipole-dipole forces?

Attractions between polar molecules

What is hydrogen bonding?

Strong attraction between H and N, O, or F

Order of IMF strength (highest to lowest)

Hydrogen bonding > Dipole-dipole > Dispersion

Which IMF causes high boiling point in CH₃OH?

Hydrogen bonding

Which compound is not a gas at room temp?

LiCl (ionic solid)

Why does ICl boil at a higher temp than Br₂?

Dipole-dipole interactions (ICl is polar)

What increases boiling point?

Stronger intermolecular forces

Are H₂O molecules polar?

Yes

Is CO₂ polar?

No (symmetrical shape cancels bond dipoles)

Which molecules can hydrogen bond?

Molecules with H-N, H-O, or H-F