Chapter 4: Chemical Bonding and Molecular Geometry

Ionic bonding

attraction between the opposite charges of a cation and an anion, complete transfer of electrons

Lattice energy

the energy required to completely separate a mole of a solid ionic compound into its gaseous ions

Coulomb’s Law

force between to particles based on their charge and size

F= k(Q1Q2/r²)

Covalent bond

bond in which two electrons are shared by two atoms

Bond enthalpy

change in enthalpy required to break a bond

Covalent compounds

relatively weak intermolecular forces, liquid, gases, low melting solids

Ionic compounds

stronger forces, solids with high melting points

Non-polar covalent bonds

electrons shared equally

Polar covalent bonds

electrons not shared equally, one atom pulls more

Electronegativity (EN)

the ability of an atom to attract electrons to itself (determines whether something is polar or non-polar)

Bond polarity

small EN difference = non-polar covalent

mid EN difference = polar covalent 

Naming binary molecules

2 non-metal elements in the formula, 2nd element gets “ide” ending, greek prefixes indicate number of atoms

Naming acids

1. anions ending in “ide” get hydro prefix, “ic” ending and add “acid” to name

2. anions ending in “ate” get “ic”, ending in “ite” get “ous” ending

Naming hydrates

greek prefixes to indicated number of water molecules

Octet rule

atoms, other than hydrogen, tend to form bonds until surrounded by 8 electrons (have a full octet)

Formal charge

a way of keeping count of electrons, the charges may or may not be real; the electrical charge difference between valence electrons and the number of electrons assigned to each atom

Resonance

a better representation of the model of an atom, must be valid lewis structures (occur when you have more than one option of a location to take electrons from)

Equivalent resonance structures

same formal charge, same number of bond types; low energy (MAJOR) structures contribute more than high energy

molecular geometry

ignores the lone pairs when naming the structure

VSEPR

valence shell electron pair repulsion

Electron domain

region most likely to find electrons in

Electron geometry

arrangement of electron domains around a central atom 

non-bonding pairs + repulsion

have greater repulsive forces causes the angles to compress

multiple bonds + repulsion

exert a great repulsive force on adjacent domains causing the angle to compress

Diatomic non-polar molecules

same element (H_2, O₂)

Diatomic polar molecules

different elements (HCL, CO, NO)

Polyatomic molecules and polarity

molecular geometry determines if there is a dipole and therefore whether it is polar or non-polar (no net dipole = non-polar, dipole moment = polar)

Isomer

same formula, different arrangement of atoms

London dispersion forces

proportional to the number of electrons in the atom

How to tell if a molecule is polar or non-polar based on the geometry?

polar= overall dipole

non-polar= dipoles cancel out