Lesson 3c Molecular View Diagrams (MVDs)

ChemCatalyst• A smelly compound is in the beaker, which

will be held at the center of the room. Raise your hand when you smell it.

• How did the molecules get (or not get) to your nose? Explain.

Senario (1) A basketball is placed on a scale. Some air is pumped into the basketball and the basketball is placed back on the scale again. Explain why the scale reading goes up after air is added.

A balloon that has been filled with air but not tied off. Air is slowly let out of the balloon. You see nothing coming out of the balloon, but small scraps of paper move across the table. However the air does not budge the rock sitting on the table. Explain how and why the paper is being moved, but the rock does not.

Three syringes are filled (with sand, with water, with air) then capped. When resting vertically, the plungers do not move. A brick is placed on the plunger of all three. Explain why only the plunger of the syringe with air moves noticeably.

Some homes heat and cook with natural gas. Natural gas is mostly a gas called methane, which is dangerous to breathe. A bad smell is added to natural gas by the gas company, so that if there is a leak, you will smell it in the house. If a leak occurs in the kitchen, explain why you would eventually smell the gas in the bedroom 1.

Rules for molecular view diagrams (MVDs)

1.Individual gas particles are dots, regardless of how many atoms they are composed of

2.Liquids are lots of dots together

3.Solids are an ordered lattice

1.Arrows represent relative speed & direction of gas motion

2.Make a “before” and “after” picture3.Use “zoom ins” to focus on important stuff4.Can explain important things in words or with

equations

The small particle model (help with MVDs)

1. All gases are made up of particles which have mass2. Particles are very small, too small to see3. Particles take up almost no space compared with the

empty space around them.4. Particles of gas are always moving5. Particles of gas do not attract or repel; they do

bounce off each other (energy conserved)6. Particles of a gas change their speed and direction as

a result of random collisions7. Particles of a gas have a very high average speed,

with some moving faster, and others moving slower

MVD’s phase 1

• Need to be descriptive & explanatory• Zoom in needs to be appropriately chosen• There always should be collisions shown• Gas motion should be random

Survey 4

For the scenario above:1. Explain the outcome based upon the small particle model.2. Draw a molecular view diagram before (compressed) and

after (uncompressed). Use one zoom in for each to support your explanation.

A heavy rock is compressing gas in a syringe (figure 1). The rock is removed, and the plunger in the syringe moves up and then stops (figure 2).

Assessment

• Diagrams must show:– Zoom in on the gas inside the syringe both times– More particles in the area when it is compressed,

or clear indication that the zoom-in window is a different size

– Random arrow directions and sizes– Collisions with the plunger on the syringe