Module 2 need to know

Types of bonds

1. ionic

2. non-polar covalent bond

3. Polar covalent bond

Electronegativity across the periodic table

increases across a period, decreases down a group

Polarity of a bond

little polarity - similar electronegativity

polar bond - different electronegativity

ionic bond - very different electronegativity

electronegativity differnce values

<0.4 - Nonpolar covalent

0.4-1.6 - polar covalent

>2.0 - ionic

1.5-2.0 - Ionic if a metal involved, polar covalent if only non-metals are involved

Hydrophobic vs hydrophilic

Polar molecules mix well in polar solvents (hydrophilic) while nonpolar molecules do not mix well in polar solvents (hydrophobic) – likes dissolves likes

Stable electron configuation

metals lose ions, achieve configuration of previous noble gas

non-metals gain ions, achieve configuration of the next noble gas

steps for writing lewis structures

1.     Calculate the sum of the valence electrons from all of the atoms.

2.     Use a line to indicate each pair of bonding electrons (2 electrons in a bond).

3.     Arrange the electrons so that each atom is surrounded by enough electrons to fill the valence orbitals of that atom

Rules for writing Lewis Structures

1.     We must include all the valence electrons from all atoms. The total number of electrons available is the sum of all the valence electrons from all the atoms in the molecule.

2.     Atoms that are bonded to each other share one or more pairs of electrons.

3.     The electrons are arranged so that each atom is surrounded by enough electrons to fill the valence orbitals of that atom. This means two electrons for hydrogen and eight electrons for second-row non-metals.

Steps for Predicting molecular structure with VSEPR:

1.     Draw the Lewis structure for the molecule.

2.     Count the electron pairs and arrange them in the way that minimizes repulsion

3.     Determine the positions of the atoms from the way the electron pairs are shared.

4.     Determine the name of the molecular structure from the positions of the atoms.

How to treat double and triple bonds in VSEPR model

the same as a single bond

configuration pt1

configuration pt2

configuration pt3

density

mass/volume

Changes of state are

physical changes, no chemical bonds are broken in the process

Intra vs Inter molecular forces

Intra - holds the atoms of a molecule together, stronger than

Inter - among molecules, cause them to aggregate

To determine the quantity of heat, Q to heat a sample from 1 temperature to a higher temperature, and a phase change is involved, you need to consider 2 quantities of heat energies

• quantity of heat energy required to increase the temperature

• quantity of heat energy required to bring about the phase change

Types of imtermolecular forces that occur between molecules

• dipole-dipole attraction

• hydrogen bonding

• london dispersion forces

dipole-dipole attraction

Exists in molecules with dipole moment

Hydrogen bonding

very strong intermolecular attraction between molecules. Where hydrogen is bound to a highly electronegative atom, such as N, O or F

London dispersion forces

Weak and short lived. Occurs in all molecules, is the most signifigant intermolecular force for non-polar molecules and the noble gases

Vapour pressure

Amount of liquid first decreases then becomes constant

Condensation - process by which vapor molecules convert to a liquid

When no further change is visible the opposing processes balance each other – equilibrium

The pressure of the vapour present at equilibrium with its liquid is called the equilibrium vapour pressure or, more commonly, the vapour pressure of the liquid

Liquids with high vapour pressures (e.g. diethyl ether) are said to be volatile – they evaporate rapidly

Liquids in which the intermolecular forces are strong have relatively low vapour pressures, because such molecules need high energies to escape to the vapour phase