Presentation on theme: "Advanced Chemistry Chapter 2. Cathode Ray Why Do This Experiment? Thompson was wanting to know the different parts of an atom He was wondering why batteries."— Presentation transcript:
Why Do This Experiment? Thompson was wanting to know the different parts of an atom He was wondering why batteries worked the way they did
The Experiment J.J Thompson built a cathode ray with one end positive (anode) and one negative (cathode). Glass was lined with fluorescent material that glowed in presence of electricity magnets were used to deflect negative particles
What he discovered Discovered that there was a stream of particles that spun a paddle wheel The magnet deflected the negative particles which proved that one part was negative and electron.
Atomic Structure This changed the atomic structure of the atom because he knew there were electrons with negative charges.
J.J Thompson Thompson received the noble prize in 1906 for discovering the electron He also could determine the ratio of electric charge to the mass of an electron - 1.76 * 10 8 c/g
History of The Experiment Ernest Rutherford had been studying alpha particles since 1898. In fact, he discovered them. In 1910 he designed an experiment to study how alpha particles interact with thin metal foils. He began his work by studying the effect of x- rays on materials.
Design of Experiment http://micro.magnet.fsu.edu/electr omag/java/rutherford/ http://micro.magnet.fsu.edu/electr omag/java/rutherford/ http://www.mhhe.com/physsci/che mistry/essentialchemistry/flash/rut her14.swf http://www.mhhe.com/physsci/che mistry/essentialchemistry/flash/rut her14.swf Rutherford shot alpha particles to see if they behaved in accordance to J.J. Thomson’s Plum Pudding experiment. They aimed a beam of alpha particles at a piece of gold foil that was aprx.8.6 x 10^(-6) centimeters thick. To be more accurate Rutherford actually included a variety of different foils like: aluminum, iron, and lead.
Design Continued… The alpha particles should have passed directly through the gold foil. So, to confirm this activity, a zinc sulfide screen was placed behind the foil as a backdrop for the alpha particles to appear on. Directly above this screen was a microscope that allowed one of the experimenters to observe any contact made between the alpha particles and the screen. In order for the light of the alpha particles to be observed, the experiment was performed in complete darkness. Also, the experimenters sat in the dark for an hour previously to the experiment. After the experiment had been set up, Geiger and Marsden (Rutherford’s assistants) would fire the beam of alpha particles through the piece of foil and observe the location at which the particles landed on the screen. For the most part, the alpha particles passed through the gold foil. However, some of particles that deflected and went to the sides of the zinc backdrop. But the biggest discovery was made when 1 in 20,000 particles would deflect approximately 90 degrees or more from the parent beam. On occasion a particle would even shoot back at the experimenter.
Model of the Atom Rutherford discovered the atom was hard in the middle because it deflected off the zinc backdrop. He came to discover the nucleus in the middle of the atom
Dalton Atomic Theory Elements composed of extremely small particles called atoms. All atoms of the same element are identical (size, mass, chemical properties) and they are different from atoms of other elements. Compounds made of more than one element bonded together, constant ratio (extension from Proust’s law of definite proportions by mass.) Law of multiple proportions if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the element are in rations of small whole numbers. Law of conservation of mass – chemical reaction
Atomic Structure Atomic number – number of protons Mass number – number of protons plus the number of neutrons. Mass # - # protons = #neutrons Isotope has a different # of neutrons.
The Periodic Table Arranged by atomic number. Columns are called groups or families and elements within the same group have similar properties since they have the same number of valence electrons. Rows are called periods. A new row is started after each filled energy level – noble gas.
Three Kinds of Elements Metals – good conductors of heat and electricity. Non-metals – poor conductors of heat and electricity. Metalloids (semi-conductors) - have properties in between metals and non- metals.
Group Names Group 1A – Alkali metals Group 2A – Alkaline Earth metals Group 7A (or 17) – Halogens Group 8A (or 18) – Noble (or inert) gases.
Molecules A combination of at least two atoms in a definite arrangement held together by chemical forces (bonds). A diatomic molecule contains two atoms of the same element – like H 2. Polyatomic molecules contain more than two atoms.
Ions Ions – when the number of positive protons for an atom or a group of atoms is different from the number of negative electrons and it has a net positive or negative charge. Why do elements make different ions? If the element makes an ion, and the ion each elements makes, depends on the number of valence electrons the element has.
Anions and Cations Anions (a negative ion) is an ion whose net charge is negative due to an increase in the number of electrons Cations have a net positive charge due to the loss of a proton or protons.
Monatomic and Polyatomic Ions Monatomic ions contain only one atom. Polyatomic ions contain more than one atom.
Chemical Formulas Molecular formulas show the exact number of atoms of each element in the smallest unit of a substance. The subscript number indicates the number of atoms of the element. For example H 2 O. Structural formula shows how atoms are bonded to each other in a molecule. Empirical formula tell which elements are present and the simplest whole-number ratio of their atoms. For example N 2 H 2, hydrazine (a rocket fuel), has the empirical formula NH.