Chem unit 6

Molecular Geometry: 

Molecular Geometry: the 3-D arrangement of atoms that constitute a molecule 

1. Square planar 

2. Linear

3. Linear 

These with the same terminal atoms will be nonpolar even though they have lone pairs on central atom 

When drawing models 

1. Add up total number of valence electrons 

2. If Carbon is present it is the central atom. Otherwise it is the farthest away from Fluorine, or the least electronegative atom. H can never be in the middle 

Exceptions to octet Rule: 

1. H and He are satisfied with only 2 electrons 

2. B, Be and Al can form bonds that have less than 8 electrons = Deficient octets 

3. 3rd row and below (heavier elements) can exceed the octet rule using empty d orbitals = expanded octet 

Resonance: occurs when a double or triple bond can be placed in different spots but between the same resonance.

• Must always draw all the possible resonance structures

• Must be indicated with an arrow 

PolyAtomic Ions: 

• If there is a plus ion remove electrons because it will be more positive 

• If there is a negative ion add electrons because it will be more negative

• Always indicate with brackets around the lewis dot structure and the ion number 

Hybridization: The combining of two or more orbitals of nearly equal energy within the same atom into orbitals of equal energy 

• the blending of atomic orbitals (s, p, d, f). Explain how the orbitals rearrange to form covalent bonds 

Steric Area/number: The number of lone pairs and bonds around the central atom’s electron region 

Water

Cohesion: attraction of molecules in a liquid to each other due to intermolecular forces 

Surface tension: tendency of liquids to minimize their surface area due to intermolecular forces 

Viscosity: resistance to flow 

Capillary Action: liquid spontaneously rising in a narrow tube due to cohesion and adhesion 

Adhesion: attraction of molecules in a liquid to their container due to intermolecular forces 

Intermolecular forces 

Intermolecular forces: attractive forces between separate molecules 3 types 

• Occurs in substances with covalent bonds

Van der Waals: category which includes all intermolecular forces 

London dispersion forces: attraction between temporary regions of high and low electron density in noble gases and nonpolar molecules

• Weakest force 

• Weak boiling point

• High vapor pressure 

• Only thing that makes non-polar substances stick together to condense from gases to liquids 

Dipole- Dipole Forces: separation of force attraction between the opposite partial charges in polar molecules 

• Medium force 

• Medium boiling point

• Medium vapor pressure 

Hydrogen Bonding: a special type of dipole- dipole force between hydrogen and strongly electronegative elements in polar molecules 

• N, O, H, F

• Not chemical bond

• Strongest force 

• High boiling point

• Weak vapor pressure 

Ion dipole interaction

• Ions can attract to polar molecules

• Ions can induce a dipole in nonpolar molecules 

Intermolecular forces = weakest 

1. London forces

2. Dipole-dipole

3. Hydrogen

Metallic bonding forces = medium 

Intramolecular forces (forces within a molecule) = strongest 

Vapor Pressure 

Vapor pressure: the pressure exerted by the gas molecules of a substance on the walls of a closed container when it is in liquid-gas dynamic equilibrium 

Factors affecting evaporation: 

1. Temperature 

2. Surface area (but NOT volume) 

3. Intermolecular forces 

The weaker the intermolecular force the higher the vapor pressure at a given temperature 

Phase changes 

Potential energy: the molecules “stored energy” the amount of space in a container 

Kinetic energy: the molecules energy of motion 

Thermal energy: heat energy required/released into or out of a system. Temperature is a measure of kinetic energy 

Phase diagrams

Phase diagram: represents the changing pressure 

• 1 Atm = universal pressure 

Critical point: represents the max temperature and pressure where the substance can be a liquid 

• Superficial fluid: exist above the critical point 

1. Highly compressed fluid with combine properties of gases and liquids

2. Ow Viscosity (fluids ability to flow) 

3. Do not have a definite phase of liquid or gas 

Critical temperature: the temperature above which a gas can not be compressed into a liquid no matter what pressure is exerted 

Critical pressure: the pressure at which raising the temperature will no longer cause the liquid to become gas 

Solids

2 types of solids 

1. Amorphous solid: considerable disorder in their structure 

2. Crystalline solids: highly regular arrangement of their particles 

Unit cell: smallest repeating pattern of a lattice extend in all directions for the structure 

Lattice: 3D system of points indicating position of ions, atoms or molecules that make up the substance 

3 types of crystalline solids 

1. Atomic solids: substances that have atoms at the lactic point

Ex: all metals 

2. Ionic solids: have ions of the points of the lattice 

Ex: NaCl 

3. Molecular Solids: have discrete covalently bonded molecules at lattice point 

Ex: ice