chem bonds

Why do atoms form bonds?

To achieve a stable configuration with 8 electrons in their valence shell.

What is an ionic bond?

A bond formed when one atom transfers electrons to another, creating oppositely charged ions that attract.

Electronegativity difference for ionic bonds

≥ 1.7

Example of an ionic compound

NaCl.

What is a covalent bond?

A bond formed when two atoms share electrons.

Electronegativity difference for polar covalent bonds

0.3–1.7

Example of a polar covalent bond

H₂O.

Electronegativity difference for nonpolar covalent bonds

< 0.3

Example of a nonpolar covalent bond

H₂.

What is a metallic bond?

A bond where metal atoms share a 'sea' of delocalized electrons.

Example of a metallic bond

Cu, Al.

How are ionic bonds formed?

When a metal donates electrons (becoming a cation) and a nonmetal accepts them (becoming an anion).

What is a formula unit?

The simplest ratio of ions in an ionic compound that balances overall charge.

Example of a formula unit

NaCl, MgCl₂.

What does Coulomb's Law describe?

The force of attraction between oppositely charged ions depends on charge magnitude and distance.

What is a crystal lattice structure?

A 3D repeating pattern of ions in an ionic solid.

Example of a crystal lattice structure

NaCl forms a cubic lattice.

What is lattice energy?

The energy required to separate one mole of an ionic compound into gaseous ions.

What dictates lattice energy?

Lattice energy increases with higher charges and smaller ion sizes.

What do Lewis structures of ionic compounds represent?

Electron transfer from a metal to a nonmetal.

Example of a Lewis structure for ionic compounds

Na donates its electron to Cl.

What is the formation of a covalent bond?

Atoms share electrons to fill their valence shells.

What is bond length?

The distance between two bonded atoms at minimum potential energy.

Bond strength comparison

Shorter bonds are stronger: triple < double < single.

What is bond energy?

The energy required to break a bond.

What do Lewis structures of molecules represent?

Shared electrons as lines between atoms.

Define single bond

A covalent bond with one pair of shared electrons.

Define double bond

A covalent bond with two pairs of shared electrons.

Define triple bond

A covalent bond with three pairs of shared electrons.

What is a polyatomic ion?

A charged group of covalently bonded atoms.

Example of a polyatomic ion

SO₄²−.

What is VSEPR Theory?

Valence Shell Electron Pair Repulsion theory states electron pairs repel to minimize repulsion.

What is electron pair geometry?

The 3D arrangement of regions of electron density (bonding and lone pairs).

Example of electron pair geometry

CH₄ is tetrahedral.

What is molecular geometry?

The 3D shape of a molecule determined by atoms only (not lone pairs).

Example of molecular geometry

Water is bent (104.5°).

What is molecular polarity?

Uneven charge distribution in a molecule due to shape and bond polarity.

Example of a polar molecule

H₂O is polar.

Define dipole

A polar bond with partial positive and negative charges.

What is a net dipole?

The overall molecular polarity resulting from the vector sum of individual bond dipoles.

Comparison of ionic compounds

Ionic often has high melting points and conducts in liquid/solution.

What is an incomplete octet?

Some elements are stable with fewer than 8 valence electrons.

Element stable with 2 electrons

Hydrogen (H): Stable with 2 electrons (e.g., H₂, HCl).

Element stable with 4 electrons

Beryllium (Be): Stable with 4 electrons (e.g., BeCl₂).

Element stable with 6 electrons

Boron (B): Stable with 6 electrons (e.g., BF₃).