Agenda Jan 21, 2020 Return Notes pages - a couple of things I noticed
Quick Check using your 13.3 notes Return notes - and I noticed a couple of areas I need to give you some additional insights. Kinetic Molecular Theory (for gases) The kinetic molecular theory is able to explain the behavior of most gases using the ideas that gas particles are very small, very far apart, moving quickly, colliding with each other and the walls of a container and that the higher the temperature the faster the particles are moving and the greater their average kinetic energy.
In liquids the particles are still moving, but there are significant attractions in between molecules that hold them closer together in the flowing liquid phase. (intermolecular attractions) Intermolecular forces in liquids can result in properties like
Viscosity - which is a measure of the resistance of a liquid to flow. It is determined by the type and strength of intermolecular forces in the liquid, the shape of the particles and temperature. As temperature increases the particles can flow more easily as they move more quickly, so the viscosity of the liquid decreases. Intermolecular forces in liquids can result in properties like
Viscosity - which is a measure of the resistance of a liquid to flow. It is determined by the type and strength of intermolecular forces in the liquid, the shape of the particles and temperature. As temperature decreases the particles slow down and so the resistance to flow increases, in other words the viscosity increases. Intermolecular forces in liquids can result in properties like Surface tension and capillary action - which we will observe more closely after the Quick Check questions. Phases
States (solid, liquid, or gas) of a substance are referred to as phases. Most substances can exist in these three phases depending on temperature and pressure conditions. When energy is added or removed from a system one phase can change into another. Freezing
Freezing point is the temperature at which a pure liquid turns into a crystalline solid. (More specifically temperature at which liquid and solid can coexist in equilibrium.) Quick Check (you may use your notes) 1) Explain what viscosity is and how it is affected by changes in temperature (be specific, increasing temperature does what to viscosity, whereas decreasing temperature...). 2) What effect does soap have on the surface tension of water? 3) How are a unit cell and a crystal lattice related? 4) What is the difference between a molecular solid and a covalent network solid? Provide an example of each type. 5) Explain why most solids are denser than most liquids at the same temperature. Turn in. Get a different colored pen out.
Correct the paper you are given. Can’t read what is written? Give them a zero. Please do correct spelling or grammar mistakes. 1.Viscosity is a measure of the resistance of a liquid to flow. It is determined by the type and strength of intermolecular forces in the liquid, the shape of the particles and temperature. (1) As temperature increases the particles can flow more easily as they move more quickly, so the viscosity of the liquid decreases.(1) As temperature decreases the particles slow down and so the resistance to flow increases, in other words the viscosity increases.(1) 2. Soaps and detergents decrease the surface tension of water. (1) 3. A unit cell is the building block of a crystal lattice, it takes lots of unit cells repeating to create the crystal lattice. (1) 4. A molecular solid is formed when molecules are held together by intermolecular forces that are weaker than covalent bonds. (1) Solid iodine is an example of a molecular solid. (1) Covalent network solids are formed when atoms are held together in a giant 3-dimensional lattice with covalent bonds. (1) Diamond is an example of a covalent network solid. (1) 5. Solids are usually more dense than liquids because their particles are held more closely together by intermolecular attractions.(1)
Write score out of 10 at top and your initials. Connecting Chemistry and Art American Chemical Society
Look at today’s labettes with eyes looking for a picture to replace a thousand words, unexpected beauty perhaps, patterns, colors and any photos you can take or sketches you can make - use the slide show with the food coloring diffusing through water pictures to share your visions. Forces in between molecules - Intermolecular forces - producing surface tension - illustrated by drops of water on a penny
How many drops of water can you fit on a penny? Make a prediction. Forces in between molecules - Intermolecular forces - producing surface tension - illustrated by drops of water on a penny
How many drops of water can you fit on a penny? Go ahead and try it. Draw/photograph the system just before all the water falls off the penny. (Do twice). Keep track of the drops. Forces in between molecules - Intermolecular forces - illustrated by drops of water on a penny Macroscale Molecular scale ? Water’s Surface tension
Source: https://www.exploratorium.edu/ronh/bubbles/sticky_water.html Within the water, at least a few molecules away from the surface, every molecule is engaged in a tug of war with its neighbors on every side. For every "up" pull there is a "down" pull, and for every "left" pull there is a "right" pull, and so on, so that any given molecule feels no net force at all. At the surface things are different. Water’s Surface tension cont. There is no up pull for every down pull, since of course there is no liquid above the surface; thus the surface molecules tend to be pulled back into the liquid. It takes work to pull a molecule up to the surface. If the surface is stretched - as when you blow up a bubble - it becomes larger in area, and more molecules are dragged from within the liquid to become part of this increased area. Water’s Surface tension cont. This "stretchy skin" effect is called surface tension. Surface tension plays an important role in the way liquids behave. If you fill a glass with water, you will be able to add water above the rim of the glass because of surface tension. Water molecules at the surface demonstrating surface tension: the surface tension for water is stronger than for other liquids because the attractions in between water molecules include Hydrogen bonds, which are stronger forces of attraction than dipole-dipole attractions or dispersion forces Forces in between molecules - Intermolecular forces Macroscale Molecular scale Forces in between molecules - Intermolecular forces - not all liquids behave like water: Compare water to methanol Fig. 13-15
Cohesion - molecules attracted to each other within the liquid
Adhesion - attraction between liquid molecules and the glass
The surface of the water in a graduated cylinder is concave because water molecules are more strongly attracted to the silicon dioxide in glass than to other water molecules. Water vs. Mercury Water vs. Mercury The cohesion between mercury atoms is stronger than the adhesion between mercury and glass. Milk - food coloring - then drops dish soap - what?
Pix or it didn’t happen. Intermolecular Forces - what holds groups of molecules together in solids and liquids?
Not thinking about ionic compounds which are solids because of intramolecular forces - attractions between oppositely charged ions (cations + and anions -) ionic bonds.
Ionic compounds dissolved in water - polar attractions between dissolved ions and the polar water molecules Intermolecular Forces - what holds groups of molecules together in solids and liquids?
Cl2 Br2 I2 Symmetrical non-polar molecules, same electronegativity, equal sharing of electrons through covalent bonds Intermolecular Forces - what holds groups of molecules together in solids and liquids? Dispersion forces (Fritz London first described)
Temporary dipole can then induce a dipole Intermolecular Forces - what holds groups of molecules together in solids and liquids? Dispersion forces
Exist between all particles
Only significant when there are no other stronger forces of attraction acting on particles
Have a noticeable effect as the number of electrons in particles increase - as with Chlorine (gas), bromine (liquid) and iodine (solid). Intermolecular Forces - what holds groups of molecules together in solids and liquids? Dipole-dipole forces
Exist between polar molecules (where the two atoms have significantly different electronegativities so that one atom in the molecule attracts electrons towards itself through the H covalent bond) Electronegativities Cl Cl = 3.16 Paulings Permanent dipole H H = 2.20 Paulings Difference = 0.96 Paulings Eg. HCl (g) Cl
Intermolecular Forces - what holds groups of molecules together in solids and liquids? Dipole-dipole forces
When there is a permanent dipole in molecules - there will be attractions between molecules - stronger than dispersion forces for molecules of about the same mass H Electronegativities Eg. HCl (g) Cl Cl = 3.16 Paulings
H H = 2.20 Paulings Difference = 0.96 Paulings Cl Intermolecular Forces - what holds groups of molecules together in solids and liquids? Extreme dipole-dipole = Hydrogen bonds
Occur between molecules that contain a hydrogen atom bonded to a small highly electronegative atom (N, O, F) which also has a least one lone electron pair.
Hydrogen bonding in Ammonia (NH3 gas)
Hydrogen fluoride Properties of 3 Molecular Compounds
Compound Molar Mass (g) Boiling Point (℃)
Methane (CH4) 16.0 -164
Ammonia (H2O) 17.0 -33.4
Water (H2O) 18.0 100