Unit 6

Unit 6

Unit 6

Unit 6: Particles with Internal Structure The Role of Charge

Q: What is the nature of electrical forces and electrical charges? We are going to look at the interaction between: Top tape (T) Bottom tape (B) Paper (P) Aluminum foil (F) ????? Observations need to be written, drawn, and recorded Top Bottom Paper Foil PVC (nr) PVC (rub)

Warm Up 1/26-27 A compound is found to 40.1% sulfur and 59.9% oxygen. Its molecular mass is 80.1 amu. What is the empirical formula? What is the molecular formula?

Q: What is the nature of electrical forces and electrical charges? We looked at the interaction between: Top tape (T) Bottom tape (B) Paper (P) Aluminum foil (F) What did we observe? Top Bottom Paper Foil PVC (nr) PVC (rub)

Q: What is the nature of electrical forces and electrical charges? Top Bottom Paper Foil R A PVC (nr) PVC (rub) Notice that the interactions fall into one of two categories: a) three attractions (one strong) and one repulsion b) two attractions and two no effects

Q: What is the nature of electrical forces and electrical charges? Top Bottom Paper Foil R A Plastic There is something unique about the repulsions If it is repelled from either T or B, it will be attracted to all the three other strips If it is attracted by both, it will not interact with the paper or foil. What’s up with that?

Q: What is the nature of electrical forces and electrical charges? Top ( ) Bottom Paper Foil Top ( ) Bottom ( ) Paper ( ) Foil ( ) Plastic ( ) Scientists have assigned a negative charge to PVC rubbed w/wool Based on your observations from using the rod, label the T and B tapes as either a (+) or (–). Make a duplicate table and enter the following: assign a positive (+) charge to objects which repel the top tape assign a negative (–) charge to objects which repel the bottom tape assign a neutral (0) charge to objects that do not repel either.

Q: What is the nature of electrical forces and electrical charges? How can you be sure something has a net charge? What happened to the force of the interaction as the objects approached each other? Does that fit with our particle model and Eph?

Model Summary Update What’s new? There is something smaller than the atom Evidence of internal structure for our atoms Particle with charge Assume atoms contain both positive and negative charges that normally cancel each other. HDYK that is the case? We will use the Thomson model of the atom a massive positive core a small number of mobile, negatively charged particles we call “electrons”. (He called them corpuscles) AKA: Plum pudding Model Evidence led J. J. Thomson to propose that in solids only the negative charges are free to move these charges are much smaller than an atom and contribute a negligible fraction of its mass

Plum Pudding Model A visual representation of this model is the “plum pudding” model– Positive cores are represented by bowls of pudding, which attract the negative electrons represented by plums. The attraction of the plums to some bowls is stronger than to others Some bowls are “stickier” The plums can move from one bowl to another because of differences in attraction (stickiness). Since plums also repel one another, you cannot put too many plums in the same bowl. Can this model explain the tapes? Top Bottom Before Separated In-contact

Applying the PPM The T tape becomes positively charged because electrons are transferred to the B tape. The overall number of electrons does not change, just their distribution on the tapes. Neutral atoms have the same amount of (+) and (–) charge. Which has a stronger attraction for the electrons, e-? Sticky side? Dull side? Notice that we once again used macroscopic behavior to explain microscopic behavior

What about the foil and paper? How were they similar? How were they different? How can we explain the difference? Charge must already be there. foil paper What is the effect of distance on the electrical force? What if a negative charge is brought nearby?

Some ideas

Examples https://phet.colorado.edu 1) Balloons and Static Electricity 2) John Travoltage

Warm Up 2/1 In the sticky tape lab, which side has a stronger attraction for the electrons—sticky or dull? Explain how you know (What evidence do you have?)

JJ Thomson’s BIG Idea He observed a cathode ray tube and noticed that he could change the path of the “corpuscles” with a magnet The direction of the deflection indicated a negative charge for the corpuscles What were Thomson’s corpuscles? electrons cathode anode glass tube

How do we apply this model to compounds? We can propose that electrical forces are involved in holding together the particles that make up pure substances. Perhaps the mobile negative charge is freer to move in some substances than in others. Foil vs. paper Metals and non-metals Conductors and insulators

Overview of the Modern Periodic Table Two distinct regions of note: Metals (M) Good conductor of electricity 2/3 of table are metals Includes transition elements (Groups 3-12) Non-metals (NM) Poor conductors of electricity All of groups 17 & 18; some of groups 14-16 Exhibit a wide range of properties

Warm Up 2/2-3 Which of the above diagrams shows atoms of a metal? HDYK? Which of the above diagrams shows atoms of a non-metal? HDYK?

Lab 6.2: Conductivity of substances and solutions

Assignment Analyze your Lab 6.2 Data Look for patterns Position on the periodic table Metals/Non-metals Write a conclusion in your journal Claim Evidence Reasoning

Exit Ticket 2/2-3 1) Based on your data from today’s lab, make a CLAIM. 2) What EVIDENCE (data) do you have to support your claim? 3) Support your conclusion with REASONING.