CHEM 12 - VSEPR Model, Polarity, KMT, IMFA

VSEPR Model (valence shell electron pair repulsion)

predicts geometry of polyatomic molecules & ions; focuses on number of electron pairs around central atom

Valence electrons

outmost energy levels; determine the chemical properties of atoms

*nth of column = n of valence electrons (eg. column 1 = 1 valence electron)

Lewis electron dot structure

structure where the symbol of element is surrounded by dots to represent valence electrons

Gilbert Lewis

American chemist who made the Lewis electron dot structure

Octet rule

8 valence electrons are needed for an atom to be stable; unstable atoms will react with other atoms until they become stable

Electronegativity

an atom's ability to attract electrons; can determine chemical bond and polarity, the nature of chemical bonds between atoms

Types of bonds

Single, double, triple, lone pairs

Geometries of VSEPR Model

Linear, bent, trigonal pyramid, trigonal planar, T-shaped, etc.

Polar molecule

uneven distribution of charge; one side of the molecule is positive, and the other side is negative

How to determine polarity (3)

- bond polarity; polar bond where electronegativity > 0

- outside atoms

- molecule shape

Symmetry/symmetrical

outside atoms are evenly distributed around central atom

Non-symmetrical

bent; outside atoms are not evenly distributed around central atom

Electronegativity difference

- gives magnitude of bond polarity shown through vector arrows

> greater than 0.4 = polar (unequal electrons)

< less than 0.4 = nonpolar (equal electrons)

Dipole

shows uncertain distribution of charge on polar molecules

Moving Matter

energy is the ability to cause changes in matter

Kinetic energy (KE)

the energy used to move

Kinetic Molecular Model (theory)

theory explaining states of matter; based on idea that matter is made of tiny particles in motion

KE and States of matter

particles only move apart with KE to overcome force of attraction; if KE increases, distances increases as well (directly proportional)

Kinetic Molecular Model

explains properties of liquids and solids in IMFA (Intermolecular forces of attraction) and KE (Kinetic energy) of particles

*IMFA depends on bond and electrons; KE depends on temperature

Intermolecular forces of attraction (IMFA)

attractive forces between neighboring particles of substances

Types of IMFA (4)

- dipole-dipole

- hydrogen bonds

- ion-dipole forces

- london dispersion (aka Van der Waals forces)

intramolecular

means within the molecule

intermolecular

means between molecule/s

Ion

an atom with a positive or negative charge

Cation

positive ion

Anion

negative ion

Non-polar

electrons are shared equally

Polar (covalently bonded)

electrons NOT shared equally

*covalently bonded

Dipole moment

measure of separation of positive and negative electrical charges in a molecule

Dipole-dipole

exists between polar molecules with permanent dipoles;

each polar molecule has unequal electron densities due to electronegativity differences;

makes partial positive and negative

Hydrogen bond

dipole-dipole interaction, but exists in molecules with H (Hydrogen) bonded to high electronegative atoms such as N, O, F (Nitrogen, Oxygen, Fluorine)

Ion-dipole forces

happens between ions (full charge) and polar molecules (partial charge);

the ion is attracted to partial charges on polar molecule leading to strong forces