AP Chemistry The Atom 2015-08-25 www.njctl.org Slide 3 / 118 - PDF document

Slide 1 / 118 Slide 2 / 118 AP Chemistry The Atom 2015-08-25 www.njctl.org Slide 3 / 118 Slide 4 / 118 Table of Contents: The Atom (Pt. A) Click on the topic to go to that section Subatomic Particles · Subatomic Particles · Atomic Modeling Return to Table of Contents Slide 5 / 118 Slide 5 (Answer) / 118 Matter Matter Atoms are classified as the basic unit of matter. Atoms Atoms are classified as the basic unit of matter. Atoms contain the following: contain the following: + + positively charged particles positively charged particles Answer protons, neutrons, electrons neutrally charged particles neutrally charged particles +1.6x10 -19 C, neutral, - 1.6x10 -19 C 1.67x10 -27 kg, 1.67x10 -27 kg, 9.1x10 -31 kg - - negatively charged particles negatively charged particles What are these particles called? What are these particles called? [This object is a pull What is the magnitude of the charges? What is the magnitude of the charges? tab] How big are these particles? How big are these particles?

Slide 6 / 118 Slide 7 / 118 Dalton's Atomic Theory 1 The basic unit of matter is.... English chemist John Dalton observed matter and drew some conclusions about atoms. According to Dalton: A an atom Matter is composed of atoms, which are indivisible. Each B an electron compound consists of a set ratio of atoms. C a neutron Atoms of same element are C C C C D a proton identical Atoms of different elements are Si C different Atoms are not changed, created, Cl Cl H H or destroyed in a reaction, they H Cl are simply rearranged Cl H Slide 7 (Answer) / 118 Slide 8 / 118 1 The basic unit of matter is.... 2 The discovery of subatomic particles disproved which of Dalton's postulates? A an atom A Matter is composed of atom which are indivisible B an electron B Atoms of the same element are identical Answer C a neutron A C Atoms of different elements are different D a proton D Atoms are not changed, created nor destroyed in a chemical reaction [This object is a pull tab] Slide 8 (Answer) / 118 Slide 9 / 118 3 Which of Dalton's postulates holds true today? 2 The discovery of subatomic particles disproved which of Dalton's postulates? A Atoms are neither created and A Matter is composed of atom which are indivisible destroyed in chemical reactions. B All atoms of a given B Atoms of the same element are identical Answer element are identical A C Atoms of different elements are different C Atoms are indivisible. D Atoms are not changed, created nor destroyed in a D Atoms of different elements are different. chemical reaction [This object is a pull tab]

Slide 9 (Answer) / 118 Slide 10 / 118 3 Which of Dalton's postulates holds true today? Dalton’s Postulates Dalton had the right idea with his postulates but he was not A Atoms are neither created and completely correct. He was limited by the equipment he had to destroyed in chemical reactions. observe reactions. B All atoms of a given Today we know that there are some forms of reactions in which mass element are identical does change, and atoms are changed from one type to another. Answer They are called Nuclear Reactions. D C Atoms are indivisible. Also remember that today we know atoms can be broken down into smaller bits. We also know all atoms of an element are not identical - D Atoms of different elements are different. elements found in nature can vary in number of neutrons. However, for the purposes of general Chemistry, Dalton's Postulates are still a pretty reasonable approximation of what is actually happening in [This object is a pull tab] chemical reactions. Slide 11 / 118 Slide 11 (Answer) / 118 . . Cathode Rays Cathode Rays In the late 1800's scientists were passing electricity through glass In the late 1800's scientists were passing electricity through glass tubes containing a very small amount of a particular gas noticed that a tubes containing a very small amount of a particular gas noticed that a beam of light was created. beam of light was created. Scientists found that they could deflect this beam by subjecting it to Scientists found that they could deflect this beam by subjecting it to an additional electrical field. an additional electrical field. + + Because the beam carried a Why would the beam deflect Why would the beam deflect negative charge! It is now known Answer toward the positive plate? toward the positive plate? that these cathode rays are + - + - electrons - - POWER POWER ON ON [This object is a pull tab] Slide 12 / 118 Slide 12 (Answer) / 118 . . Charge to Mass Ratio Charge to Mass Ratio Once these rays were understood to be particles, they were in search Once these rays were understood to be particles, they were in search of their properties - like their mass and the size of their charge. of their properties - like their mass and the size of their charge. A very weak electrical field could deflect the beam a great deal. The A very weak electrical field could deflect the beam a great deal. The mass/charge ratio was determined to be 1.76 x10 11 C/kg. mass/charge ratio was determined to be 1.76 x10 11 C/kg. + + deflection deflection It must have either a Answer + - + - really small mass (small things are easier to move than big things) or - - a really large charge (opposites attract). POWER POWER ON ON What does this tell us about the particle? What does this tell us about the particle? [This object is a pull tab]

Slide 13 / 118 Slide 14 / 118 . . Determining the Mass & Charge Using Charge to Mass Ratio A scientist named Millikan squirted oil drops into a box and then passed high energy x-rays at the box hoping to knock electrons off Once the charge was known, it was easy to use Thomson's charge to the air molecules and onto the oil drops. mass ratio to find the mass. 1.6 x10 -19 C x 1 kg = 9.09 x 10 -31 kg Oil drops 1.76 x10 11 C + X-rays This is one tiny mass! - Electrons are super super small. Click here to see an animation of the experiment By measuring the energy necessary to stop the drops from descending, he was able to determine the charge per drop. The more energy needed to prevent the drop from falling, the smaller the charge of the drop. Slide 15 / 118 Slide 15 (Answer) / 118 4 What characteristic about the cathode rays led them 4 What characteristic about the cathode rays led them to believe they were negatively charged? to believe they were negatively charged? A They were small A They were small Answer B They were easily deflected B They were easily deflected C C They were deflected towards a positive electrode C They were deflected towards a positive electrode D They moved quickly D They moved quickly [This object is a pull tab] Slide 16 / 118 Slide 16 (Answer) / 118 5 Which one of the following is not true concerning 5 Which one of the following is not true concerning cathode rays? cathode rays? A They originate from the negative electrode. A They originate from the negative electrode. B They travel in straight lines in the absence of B They travel in straight lines in the absence of Answer electric or magnetic fields. electric or magnetic fields. C C They move from the anode to the C They move from the anode to the cathode. cathode. D They are made up of electrons. D They are made up of electrons. [This object is a pull tab]

Slide 17 / 118 Slide 17 (Answer) / 118 6 The magnitude of the charge on an electron 6 The magnitude of the charge on an electron was determined in the __________. was determined in the __________. A cathode ray tube, by J. J. Thomson A cathode ray tube, by J. J. Thomson Answer B Millikan oil drop experiment B Millikan oil drop experiment B C Dalton atomic theory C Dalton atomic theory D D atomic theory of matter atomic theory of matter [This object is a pull tab] Slide 18 / 118 Slide 19 / 118 . . Discovery of the Proton Discovery of the Proton After the discovery of the electron, scientists believed that there must The anode rays were referred to as protons, which were found to be also be a positively charged particle in the atom. To look for significantly heavier than electrons. these, they used an anode ray tube. 1 proton = 1840 x mass of electron - Power Since the heaviest anode rays in oxygen were found to be 8 x heavier Positive than those in hydrogen, it was assumed that oxygen had 8 protons anode rays compared to hydrogen's 1. The number of protons an atom has is different for each element on the periodic table. + By placing holes in the cathode so particles could move through it, they found that particles were indeed moving from the anode to the cathode. Since they move towards a negative plate, they must be positive. Slide 20 / 118 Slide 20 (Answer) / 118 7 Which of the following is TRUE regarding 7 Which of the following is TRUE regarding protons? protons? A They were originally called cathode rays A They were originally called cathode rays B They move faster than cathode rays B They move faster than cathode rays Answer C They have a larger mass than electrons C They have a larger mass than electrons C D They moved from the cathode to the anode D They moved from the cathode to the anode [This object is a pull tab]