Unit 2 Flashcards
Why do bonds form?
The molecule has a lower energy - becoming more stable then separated atoms.
Ionic - ions formed
Covalent - electrons shared
Ionic Bonding
Electrostatic forces of attraction between oppositely charged ions
Ionic solids form because oppositely charged ions are attracted to each other in all directions. - non-directional bond
Difference in Electronegativity
Electronegativity
The ability of an atom in a molecule to attract electrons toward itself, Increasing effective nuclear charge, you can more easily attract electrons to the nucleus
Most electronegative element
- Down a column, atoms get less electronegative. Atoms are getting bigger, adding more orbitals. The attraction will be little.
Lewis Structure Bonding
Total valence electrons, draw covalent bond (2 electrons) between atoms and central atom.. Give out remaining electronegative atoms as lone pairs, if not full form multiple bonds.
Valence Shell Electron Pair Repulsion Model
Shapes of molecules arise from electron groups arranging them as far apart from others to minimize repulsion
Linear
Not counting these lone pairs because we are looking at the CENTRAL ATOM
2 electron groups around central atoms
Trigonal planar
More than one shape.
Around carbon - trigonal planar
Around nitrogen - trigonal planar
The double bond pushes the angles (not exactly 120 degrees)
TRIGONAL PLANAR - 3 electron groups around central atom
Tetrahedral
Trigonal pyramidal or tetrahedral
- Either way, it has four electron groups, that lone pair is occupying one of the sights
Trigonal bipyramid
expanded octet
SF4
seesaw
Octahedral
Lone pairs still effect the shape
6 electron groups
Dipole Moment
DIPOLE MOMENTS : a measure of the separation of charge in a molecule arising from the unequal sharing of electrons in polar bonds
Symmetry - symmetrical = cancel
Intramolecular Forces
FORCES WITHIN MOLECULE
Intermolecular forces
FORCES OUTSIDE OF MOLECULES
Ion-dipole attraction
Interaction between fully charged ion and partial charges of a polar molecule, energy of attraction increases with the charge of the ion and decreases with the square of the distance between the ion and dipole
Attraction energy = increases with the charge on the ion and decreases with the square of the distance between the ion and dipole.
Need to have an ionic compound and a covalently bound compound with a dipole moment = this interaction is only in mixtures.
Dipole Dipole interactions
In order to have dipole-dipole interactions = has to be polar molecules. Attraction between opposite charges.
there are repulsions that help orient the like charges.
Hydrogen Bonding
Hydrogen bond - intermolecular force - between molecules,
Special case of dipole-dipole
Ice floating on liquid water - less dense. Ice forms crystals that are less dense then water, partially because of the strong hydrogen bond.
Electronegativity difference is great in hydrogen bonding - strongest intermolecular force
London Dispersion Forces
Molecules that have no dipole moment - ex. Neon has no dipole moment —- but, electrons can randomly move about and concentrate in one region more than another. Making a partially negative and positive charge - INSTANTANEOUS DIPOLE
Then they can concentrate in a different region. Random movement of electrons, causing dipole moment
Polarizable
Can be distorted
Pressure
Force exerted over an area, Measuring pressure - manometer (closed tube). Tube stuck into mercury filled disk - have atmospheric pressure pushing on the dish - it will rise until the force of gravity makes the pressure balanced - then gives us the height. Forces proportional to the gravity
Ideal gas
- Gases made of tiny particles moving completely randomly
- Total volume of particles very small compared to size of container
- Particles do not interact with each other
- Particle Collisions are elastic
- Kinetic energy increases with temperature
Pressure resulting
Results from gas particles colliding with container walls
Charles Law
At same P and fixed n, Volume is proportional to the temperature
V=k2T
Increasing temp - molecules move faster. Gas exerts more pressure on the lid. The lid moves out until gas is balanced with the external pressure. Keeping pressure constant - allowing volume to move
Effusion
Escape of a gas through a hole into a vaccum
Diffusion
movement of one gas through another
Crystalline solids
Well ordered matter within the solid - arrangement of atoms in the solid repeats itself.
Very well ordered at the molecular level
Molecular Solids
Held together by intermolecular forces - low melt points
Covalent network solids
Extended structures of atoms held together by covalent bonds - very high melting points
Allotropes
- different structural forms of an element
One super molecule - lots of covalent bonds
Have to chop up covalent bonds to melt…
Metallic Solids
Metallic bonding between atoms - metal atoms as cations in sea of delocalized electrons, high electrical conductivity, malleable
Ionic Solids
Held together by electrostatic attraction between cations and anions - rock salt structure
Liquids
Most liquid are molecular - IMF keep particles close, but they are not strong enough, particles move past each other.
Have some special properties for liquids
Surface tension - amount of energy required to expand a liquid surface.
IMF stabilizing in liquids
water molecule in the middle has more stabilizing interactions. Lower the energy when the surface area is smaller.
The stronger the forces between particles in a liquid, the greater the surface tension.
Capillary action
rising of a liquid in a narrow space against the pull of gravity
Cohesive forces
Forces between molecules
Adhesive forces
Forces between molecules and container walls
states
Solid to liquid - melting
Liquid to gas - vaporization
Gas to liquid - condensation
Liquid to sold - freezing
Gas to solid – deposition
Solid to gas - sublimation
Breaking attractive forces
endothermic
ADDING HEAT - INCREASE IN KE - OVERCOME ATTRACTIVE FORCES
Forming attractive forces
releases energy, exothermic
Water changing state
Start at -40 degrees. Adding heat, increasing kinetic energy.
At 0 degrees we reach a plateau - mix of solid and liquid, energy goes to overcoming IMF
NOT BREAKING BONDS - water molecule isn’t changing (heat of fusion)
Stays at plateau until completely liquid.
Adding heat, liquid water KE increases, molecules moving faster.
Plateau at 100, heat of vaporization, then it goes into a gas (all water evaporated)
Thermodynamics
want to know when a phase change is a spontaneous process
To know if something is spontaneous, we need to know about the free energy = negative for spontaneous
Gas - liquid equilibrium
Air in vacuum, below boiling point some molecules will vaporize.
Vaporization initially, but when the molecules are In the gas phase, condensation can occur.
Condense and vaporize at the same state - equilibrium.
Leveled off pressure
At 25 degrees - below boiling point, some is evaporating
Vapour pressure depends on temperature - increase in temp, liquid has more KE, more molecules can escape.
Gas sample has a distribution of KE
Summing at a given temperature
That KE distribution depends on temperature
Liquid - molecules are moving, they need enough KE to move to different state (escaping the liquid)
Solutions
One or more substances (solutes) mixed at the molecular level (dissolved) in a medium (solvent (usually liquid)). Many reactions take place in solution
Forming a solution
For substances to form a solution, the solute-solvent interactions has to overcome both solute-solute interactions and solvent-solvent interactions
Substances with similar intermolecular forces form solutions - like dissolves like
Freezing point depression
solutes lower freezing point of the solvent
boiling point elevation
solutes raise boiling point of the solvent
Vapour pressure lowering
solutes decrease vapour pressure of the solvent
Non volatile solutes decrease vapour pressure of solvent (won’t contribute to vaporization) - raoults law - mole fraction of solvent times vapour pressure of pure solvent equals the vapour pressure of solvent
Volatile Solutes - both components of mixture contribute to vapour pressure, have to find Pressure of each then add them
Osmotic pressure
pressure that must be applied to a solution to prevent osmosis from a sample of pure solvent
Colligative properties
solution properties depend on concentration of solute, not its identity - need total concentration of everything in solution
II=MRT
