S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 1 UNIT 4 NOTES: ATOMIC THEORY & STRUCTURE STUDENT OBJECTIVES: Your fascinating teachers would like you amazing learners to be able to 1. Provide a brief outline of the historical development of the periodic table including contributions from: Mendeleev, Moseley, and Seaborg. 2. Identify metals, non-metals, and metalloids on the periodic table. 3. Locate the following groups on the periodic table: Alkali metals, Alkaline Earth Metals, Transition Metals, Halogens, Noble Gases. 4. Compare and contrast physical properties of the following groups: Alkali metals, Alkaline Earth Metals, Transition Metals, Halogens, Noble Gases. 5. Describe the contributions to atomic theory by Dalton, JJ Thompson, Rutherford, Bohr, Schrodinger, and Heisenberg. 6. Outline the cathode ray experiment. 7. Explain the results of the gold foil experiment. 8. Identify the three primary subatomic particles in terms of size, location, and charge. 9. Compare and contrast atomic number, mass number, atomic mass 10. Compare and contrast the impact on an atom of changing the number of electrons, neutrons, and proton. 11. Perform calculations involving numbers of protons and electrons and the ionic charge of a species. 12. Define the terms cation and anion. 13. Identify the isotopes of an element. 14. Perform calculations involving atomic mass and % abundance of isotopes.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 2 I. THE PERIODIC TABLE: A. History: The periodic table has gone through A LOT of changes throughout history!!! The scientific process was definitely at work! I m Johann Döbereiner around 1817, I began to recognize the relationship between properties of triads of elements and their atomic mass. Some of the triads I distinguished include Li, Na, K and Ca, Sr, Ba. These were the first glimpse of GROUPS or FAMILIES of elements! My name is John Newlands around 1865, I published my findings that when the elements were arranged by increasing atomic mass, every 8 th element seemed to have similar properties! Oh, and have you seen my epic beard?!? I m Dimitri Mendeleev, and I am far more famous than my two predecessors (and I have a better beard)! Around 1870, I published a version of the periodic table that was arranged according to atomic mass. I wisely included blanks for unknown elements that I predicted would later be discovered. My table provided a foundational framework for your current version! My name is Henry Moseley. Mendeleev was on the right track, but his table needed a little tweaking. After doing some research with x-ray spectroscopy around 1913, I found that if we arranged the elements according to atomic number instead of atomic mass, the groups made much more sense. This is how current periodic tables are arranged! I also have a pretty sweet moustache. I m Glenn Seaborg while Moseley suggested the idea of the Lanthanides & Actinides, I began to bombard particles together in order to create those elements. In the 1940 s, I helped to synthesize many of the elements that are found in those bottom two rows of the periodic table. I suggested that pulling them out of the main body of the table would better reflect properties within groups and make the table a little neater! I even have an element named after me element 106 is Seaborgium.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 3 B. Organization Using page 131 in your book, or using the internet, label the periodic table found below according to the following guidelines. (NOTE: Your key will not look exactly like the book!!!) a. Color all metals blue b. Color all non-metals yellow c. Color all semi-metals (metalloids) green d. Draw a dark line showing the break between metals and non-metals (the line by the semi-metals) e. Label the location of the Alkali Metals f. Label the location of the Alkaline Earth Metals g. Label the location of the Transition Metals h. Label the location of the Halogens i. Label the location of the Noble Gases j. Label the location of the Lanthanides k. Label the location of the Actinides l. Show with a labeled arrow the direction that groups travel on the periodic table m. Show with a labeled arrow the direction that periods travel on the periodic table
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 4 C. Properties of selected groups: At the conclusion of the Periodicity Challenge, fill out the following chart about the groups on the periodic table. Group 1 Group 2 Group 17 Group 18 Name Metal or nonmetal? State at 25 o C and 1 atm Malleable and ductile (Y or N) Conducts electricity (Y or N) Key physical properties (color, texture, relative melting/boiling points, density, and luster) Key chemical properties NOTICE: Elements that are in the same group have similar! This is because if they re in the same group, they have the same number of. SOMETHING TO THINK ABOUT: Elements in Groups 3-12 are known as the Transition Metals. Based on the fact that they are metals, make some predictions about the properties of these elements. II. HISTORY OF ATOMIC THEORY - the smallest particle of matter which will exhibit the properties of that element. When broken down smaller than an atom, the parts (protons, electrons, and neutrons) of different elements look exactly the same. You cannot tell a proton in a gold atom from a proton in oxygen gas. Atoms are very small typically about 1 x 10-8 cm in diameter. To give you an idea of how small this is: 1.0 gram of lead contains 2.9 x 10 21 atoms of lead. By comparison, the earth s entire population is only 6 x 10 9 people.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 5 Models: People use models to describe understanding of truth. The models we have of the periodic table have changed over time at improved technology was used to study the atom. There were MANY scientists involved in this process, but we will focus on a few of the main ones. A. JOHN DALTON was an Englishman in the 19 th century who was the first to develop and publish a theory about how atoms looked and behaved. He conceived of the atom as a solid sphere, much like a billiard ball. Hence, his theory was called the. The following are statements of John Dalton s ATOMIC THEORY: (1) Proposed: all elements are composed of very small particles called atoms - which are indivisible. He thought you could not split an atom into smaller pieces! : Today we know that atoms can be divided into protons, electrons, neutrons and almost 200 other subatomic particles. (2) Proposed: All atoms of the same elements are identical. : We know that this is not true due to the presence of isotopes. Isotopes are atoms with the same number of protons (same element) but different numbers of neutrons (different masses). For example, carbon-12 has 6 protons and 6 neutrons, but carbon-14 has 6 protons and 8 neutrons. (3) Proposed: Atoms of different elements are different. (4) Proposed: Atoms of different elements can combine with each other only in simple whole number ratios to form compounds. (5) Proposed: Chemical reactions occur when atoms are separated, joined or arranged. However, atoms of one element ARE NOT changed into atoms of another element by a chemical reaction. (Only by nuclear reactions, which are different!) B. J. J. THOMSON discovered both electrons and protons by means of his CATHODE RAY TUBE EXPERIMENT! (1) Proposed: Through the Cathode Ray Tube Experiment, he proposed that electrons are negatively charged particles, abbreviated e ; very lightweight their mass is considered negligible when describing the mass of an atom because they only weigh about 1/1839 the mass of a proton or neutron. CATHODE RAY TUBE EXPERIMENT + Magnetic field - Magnetic field Electron Stream without applied electric field Electron Stream after applying field, + on top, on bottom Notice how the electron stream bends toward the + plate and away from the plate. Thomson knew that electrons must be negative because they are attracted to the positive field! (Remember, positive attracts negative.) Also: Since the e stream could be produced from any metal, Thomson suggested that all atoms had electrons and they were negatively charged.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 6 (2) Proposed: Thomson conceived of the atom as a plum pudding model the protons and electrons were mixed together like a fruit salad (or plum pudding). The pieces of plum were the electrons swimming in a pudding that was positively charged. C. ERNEST RUTHERFORD worked for Thomson in his lab for a while. He performed the GOLD FOIL EXPERIMENT. (1) Proposed: the atom as mostly space and that all of the positive charge was located in a very small central nucleus. GOLD FOIL EXPERIMENT RESULTS: 1. Most particles went through (which is what was expected) 2. Some were slightly deflected (hmm.) 3. Some were deflected back and missed the fluorescent screen (HMMMMMMM.) Why did some of the particles get deflected? Reason: the positive alpha particles were hitting the positive, small, dense nucleus and getting deflected (since positive repels positive). Conclusions: Dense positive nucleus (meaning plum pudding was incorrect). Negative electrons were moving around the nucleus. THE ATOM IS MOSTLY EMPTY SPACE. SO.. Basically, Thompson discovered, while Rutherford discovered that the nucleus was positive, meaning the atom has in it. Which of Dalton s points did Thompson & Rutherford prove was wrong??!?! D. NIELS BOHR Danish scientist who originally worked for Thomson and Rutherford. Chemistry is never BOHR-ing! (1) Proposed: Electrons were in energy levels. The further an electron was from the nucleus, the higher its energy. This proposal provided a great starting point for our current understanding of the atom YEAH BOHR!! (2) Proposed: the planetary model of the atom in which the electrons orbit the nucleus much as the planets orbit the sun.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 7 E. ERWIN SCHRODINGER an Austrian physicist, along with Werner Heisenberg and Louis de Broglie, postulated the quantum (wave) mechanical model of the atom - which is the most current model we have! In this concept, the electrons do not actually orbit the nucleus, but are found only in areas based on the amount of energy they have, and move according to wave functions. The key of the model is that we don t really know exactly how an electron moves just the probability of finding it in a particular region of space around the nucleus. We will talk WAY more about Schrodinger s model next unit! Looks like a few electrons went through my hair!!! And don t even get me started about cats MEOW? III. THE COMPONENTS OF AN ATOM A. - positively-charged particle which is found in the nucleus; it is considerable more massive than the electron (1837 times heavier). Shown as p +. B. - very light negatively-charged particle which is found somewhere outside the nucleus. Its mass is considered negligible when determining the mass of an atom. It weighs only 1/1837 that of a proton, but its negative charge is as powerful as the positive charge of a proton. Shown as e. C. - a particle found in the nucleus which is approximately the same mass as a proton but does not have an electrical charge associated with it it is neutral. Shown as n o. D. ARE ALWAYS NEUTRAL PARTICLES that is, they contain the same number of protons as electrons (and it doesn t matter how many neutrons they have) E. the number of protons found in the nucleus of an atom. On the Periodic Chart it is the large whole number in the upper corner. Notice that the only thing which makes on element different from another one is the number of protons it contains. An atom with 6 protons is carbon; an atom with 5 protons is boron and an atom with 7 protons is nitrogen. ATOMIC NUMBER DEFINES ONE ELEMENT FROM ANOTHER! NOTE THE DIFFERENCE BETWEEN ATOMIC MASS AND MASS NUMBER! F. the number of protons and neutrons found in the nucleus of an atom, this DOES NOT show on the Periodic Table. The atomic mass (which does show on the Periodic Table) is an average of all the different isotopes of that element (on the next page). # of n 0 + # of p + = mass # We often use mass number to describe what isotope (same element, different # n 0 ) we are talking about. For example, Carbon-14 means that we are talking about the carbon that has a mass number of 14. Example 4-1. How many neutrons are in Uranium-235?
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 8 IV. CHANGING ATOMIC STRUCTURE: A. Changes in the number of formation of Isotopes differ in the number of neutrons and hence the Isotopes typically behave chemically the same. Isotopes are often designated with their mass number hyphenated after the element name: Example: Carbon-12 Carbon-13 Carbon-14 Each has 6 protons and 6, 7, and 8 neutrons respectively. The atomic mass given on the Periodic Table for each element is really an average of the masses of all the isotopes of that element, weighted by their percentage of abundance. Avg. Atomic Mass = (fraction isotope #1) (mass of #1) + (fraction isotope #2) (mass of #2) + (fraction of isotope 3) (mass of #3) +. which continues on for however many isotopes you have!!! AtomicMass Fractional Abundance MassNumber isotopes The fraction abundance is simply the percent 100 NOTE: We express this in decimal form! If exact masses are given, use the exact masses. If not, use the mass numbers. HELPFUL HINT: The sum of the percents should be, so the sum of the fractions should be. Example 4-2. Naturally occurring chlorine is 75.53% chlorine-35 and 24.47% chlorine-37. What is the average atomic mass which should be placed on the Periodic Table for the element? Example 4-3. The element neon consists of three isotopes with masses of 19.99, 20.99 and 21.99 amus. These three isotopes are present in nature to the extent of 90.92%, 0.25% and 8.83% respectively. Calculate the atomic mass of neon. Example 4-4. The element silver consists in nature of two isotopes, Ag-107 and Ag-109. The accepted atomic mass of silver is 107.87 amu. What are the percentage of abundance of Ag-107 and Ag-109?
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 9 B. Changes in the number of formation of IONS particles which do not have the same number of protons and electrons so therefore they do have an electrical charge associated with them. IF: # p + > # e IF: # p + < # e THEN: there is an excess charge. CALLED: THEN: there is an excess charge. CALLED: # protons # electrons = ionic charge NOTE: When adding and subtracting electrons you are dealing with adding a negative charge (making more negative) and subtracting a negative charge (making more positive). Gain of electrons Loss of electrons 3 2 1 0 +1 +2 +3 Example 4-5. An element has 20 protons and 18 electrons. Identify the element and determine the ionic charge. Example 4-6. The sulfide ion has a charge of 2. How many protons and electrons does this ion have? C. Changes in the number of formation of Changes in the number of protons occurs during Various particles are emitted or captured to form Typically accompanied by energy in the form of V. NUCLEAR SYMBOL The NUCLEAR SYMBOL is a way of writing atoms or ions which gives you lots of information. Mass number Atomic number 16 2- O 8 2 Ionic charge Number in a compound We won t be dealing with the number of the atoms in a compound until a later unit, so leave the lower right hand side blank for now.
S T U D E N T N O T E S P r e - A P C h e m i s t r y U N I T 4 Page 10 Example 4-7. Complete the following table. Protons Electrons Neutrons Mass # Atomic # Charge NUCLEAR SYMBOL 5 5 6 6 8 14 18 32 2 10 14 +3 28 24 +2 18 31 3 VI. HOW IMPORTANT IS CHARGE??? Na : Na +1 :