CHM101 Lab The Periodic Table and Atomic Structure Grading Rubric

Transcription

1 Name Team Name CHM101 Lab The Periodic Table and Atomic Structure Grading Rubric To participate in this lab you must have splash- proof goggles, proper shoes and attire. Criteria Points possible Points earned Lab Performance Printed lab handout and rubric was brought to lab 3 Safety and proper waste disposal procedures observed 2 Followed procedure correctly without depending too much on instructor or lab partner 3 Work space and glassware was cleaned up 1 Lab Report Part A (accurate observations of known samples 1.5 Part A (correct identification of unknowns) 1.5 Part B (properties table complete and correctly filled out) 2.5 Part B (conductivity correctly observed) 1 Part C (isotope table correct and complete) 1.5 Part D (electron configuration table correct and complete) 1.5 Part D (orbital diagram table correct and complete) 1.5 Total 20 Subject to additional penalties at the discretion of the instructor.

2 The Periodic Table and Atomic Structure Goals To observe properties of various elements and describe their atomic structure. Background Properties of Elements This lab will explore various properties and structure of elements. Different elements give off various colors when they absorb then release energy from heat or electricity. Fireworks come in multiple colors because the salts of different elements are mixed into the gunpowder. One of the ways scientists in the 1800 s proved that they isolated a new element was through the characteristic color light the new elements emitted in a flame. The light was passed through a prism revealing a line spectrum light separated into colored lines. The line spectrum is a type of elemental finger print no two elements have the same spectrum. In this lab you will look at the colors of light given off by elements sprayed into a flame. You will then compare these colors to the colors of unknown solutions to determine the unknown identities. Elements on the periodic table can be classified as metals, non- metals or metalloids. The zigzag line on the table separates the metals from the nonmetals. The metals make up over 75% of known elements and are found on the lower left side of the table. Metals are shiny, good conductors of heat and electricity, and malleable (can be pounded into sheets). Nonmetals are found on the upper right corner of the periodic table. Nonmetals are dull, poor conductors of heat and electricity, and brittle. Metalloids, or semi- metals are located on the zigzag line of the periodic table. Aluminum touches the line, but is considered a metal. Metalloids have properties that are intermediate between metals and nonmetals. They tend to be shiny, brittle, and average conductors of heat and electricity. Elements can also be categorized by their group. The word periodic refers to the fact that properties of elements in the table repeat. Elements are arranged in columns, or groups, on the periodic table where all elements in the group have similar properties. For instance, all elements in group 8A, the noble gases, are unreactive. Elements in group 1A, the alkali metals, are highly reactive and produce hydrogen when mixed with water. Other named groups include the alkaline earth metals (2A), the halogens (7A), and the transition metals (elements in the block between 2A and 3A). Atomic Structure All atoms consist of the same subatomic particles: protons, neutrons, and electrons. The nucleus of an atom contains protons, positively charged particles, and neutrons, negatively charged particles. Protons and neutrons make up most of the mass of the atom. Compared to the overall size of the atom, the nucleus is very small and thus very dense. The number of protons in the nucleus defines an element. For example, all carbon atoms have 6 protons. The atomic number, listed above each element symbol in the periodic table, represents the number of protons in the nucleus. The number of neutrons in the nucleus varies for each element. Carbon can have 6, 7, or 8 neutrons in its nucleus. Atoms of the same element with different number of neutrons are isotopes. The mass number of an isotope is equal to the

3 protons plus the neutrons. A carbon atom with 6 neutrons has a mass number of 12, its isotope symbol is written as 12 C and is called carbon- 12. A carbon atom with 8 neutrons has a mass number of 14, its isotope symbol 14 C, and is carbon- 14. Electrons are negative particles that occupy the vast empty space around the nucleus. If an atom is neutral, the number of electrons equals the number of protons. Electrons have roughly 1/2000 th the mass of protons and neutrons therefore do not contribute significantly to the mass of an atom. The arrangement of electrons in an atom determines its reactivity. Electronic Structure There are several layers of structure to how electrons are arranged in atoms. Electrons are arranged into energy levels which contain one or more sublevels, and each sublevel contains one or more orbitals which hold up to two electrons each. Energy levels are given numbers starting at n = 1. The higher the n number, the further from the nucleus the electrons are. Sublevels are given letters: s, p, d, f. The higher the energy level, the more sublevels it contains. The n=1 energy level has one sublevel, the 1s. The n=2 energy level contains two sublevels: 2s and 2p. The n=3 energy level contains three sublevels: 3s, 3p, and 3d. All s sublevels have 1 orbital and up to two electrons, p sublevels have 3 orbitals and up to 6 electrons, d sublevels have 5 orbitals and up to 10 electrons, f sublevels contain 7 orbitals and up to 14 electrons. Electrons fill the lowest energy sublevels first, which generally corresponds to filling from low n to high n energy levels, though there are some exceptions. The structure of the periodic table tells the order that sublevels fill in. Groups 1A and 2A are known as the s block elements in those groups represent electrons filling different s sublevels where the energy level is equal to the period number. The period 3 s block (Na, Mg) is the 3s sublevel. Groups 3A to 8A are the p block, with energy level corresponding to the period number. The period 2 p block (B to Ne) is the 2p sublevel. The transition metals are the d block, with energy level one behind the period number. The period 4 d block (Sc to Zn) is the 3d sublevel A (H & He) 1s 2s 3s 2A 3A 4A 5A 6A 7A 8A 2p 3p s 3d 4p 5s 4d 5p 6s 7s La-Lu 4f Ac-Lr 5f 5d 6d 6p Electrons Configurations and Orbital Diagrams An electron configuration is a description of levels and sublevels where electrons are for a particular atom. Each sublevel is written followed by a superscript number indicating the number of electrons in that sublevel. For instance, the electron configuration for hydrogen, which has one electron, is 1s 1 hydrogen has one electron in the 1s sublevel. The configurations get longer as we get to elements with more electrons. The electron configuration of phosphorous, which has 15 electrons, starts by filling the 1s subshell. The 1s only holds two electrons, so we need to find what fills next by looking for element 3. This would be Lithium which is in the 2s block, meaning the 2s fill next with another two electrons. We are up to 4 electrons, so we go to element 5, boron in the 2p. The 2p fills next with 6 electrons bringing us to 10 electrons. Element 11, sodium, is in the 3s, filling next with 2 electrons bringing the total to 12. Finally element 13 is in the 3p, which we give 3 electrons bringing the final electron count to 15, the atomic number of phosphorous. The final electron configuration is: 1s 2 2s 2 2p 6 3s 2 3p 3

4 Electron configurations get quite long for the later elements, so the abbreviated electron configuration is often used. To write and abbreviated electron configuration, write the symbol of the noble gas that comes before your element in brackets, then only write the sublevels that follow. For phosphorous, the noble gas before it is Neon which has 10 electrons. The electron configuration of neon is 1s 2 2s 2 2p 6 ; this gets replaced as [Ne], making the abbreviated electron configuration for magnesium: [Ne]3s 2 3p 3 The only important electrons for reactivity are those in the outermost energy level (the highest n) which are known as valence electrons. Valence electrons for phosphorous are the electrons in the n=3 energy level 2 in the 3s and 3 in the 3p for a total of 5 valence electrons. Note that phosphorous is in group 5A of the periodic table the A group indicated the number of valence electrons for all elements in that group. Electrons in inner energy levels are known as core electrons and are not reactive. The core electrons for phosphorous would be the 10 electrons in the n=1 and n=2 energy levels. Orbital diagrams are another way to depict where electrons are in an atom. Each orbital is represented as a box with arrows inside representing the electrons. s sublevels have one box for their one orbital. p sublevels are drawn with three connected boxes for their three orbitals. In a box, we draw one arrow up and one arrow down to indicate opposite spins of electrons. In a sublevel, each orbital gets one electron of the same spin before pairing. The orbital diagrams for hydrogen and phosphorous are below. Compare these to their electron configurations. Laboratory Activity Materials: NaCl, KCl, CaCl 2, CuCl 2, SrCl 2, BaCl 2 in 50% ethanol Bunsen burners hoses unknown solutions 1-3 element sample bottles samples of Cu, Zn, C, Si conductivity probe periodic tables Procedure A. Flame tests 1. Your instructor will set up two Bunsen burners on opposite sides of the room for groups to share. Do not put any objects on these benches for duration of the experiment, especially the spray full of flammable liquid! 2. Hold the spray bottle for the unknowns one foot from the flame and spray up to 3 times to determine the color of each element. Most flames will have a background color of orange from the ethanol combustion look for the other colors in the flame. When done, return the bottle to the instructor s bench. Do not place it on the bench with the Bunsen burner. 3. Repeat the procedure for the three unknown solutions. Determine their identity by comparing to the colors of the known colors. Safety! Tie back long hair and be careful of loose clothing around the flame. Do not walk behind the Bunsen burner flame while the flame tests are occurring Hold the spray bottle 1 foot from the flame when spraying. Each group should only need 2-3 sprays to identify the color. Do not put down spray bottles on the bench with the Bunsen burner! Return to instructor s desk when not in use. Do not put anything else flammable on the bench with the Bunsen burners including your lab report!

5 B. Properties of Elements 4. Observe the properties of various elements samples in the labeled bottles. Completely fill out the element properties table in the data sheet. If an element does not belong to a named group, write the group number (ex 4A) in the last column. 5. Touch the two wire ends of the conductivity probe to the four elements in the conductivity table. If the LED lights, the circuit was completed meaning that the element conducts electricity. C. Atomic Structure 6. Use your periodic table to complete the isotope table. Recall that the number under each element in the periodic table is the average atomic mass, not the mass number. That number represents the weighted average mass of all isotopes. The mass number on the isotope is the mass of one particular isotope. C. Electronic Structure 7. Complete the electron configuration table using noble gas abbreviation. Identify the number of valence electrons for each element. 8. Complete the orbital diagram table. Waste Disposal Return all materials to the supplies bench.

6 Periodic Table and Atomic Structure: Data Sheet Name A. Flame Tests Solution Element Observed Color NaCl KCl CaCl 2 SrCl 2 BaCl 2 Na K Ca Sr Ba Unknown Observed Color Element A B C B. Properties of Elements Element Symbol Atomic Number Aluminum Bismuth Carbon Copper Helium Iodine Magnesium Mercury Nickel Oxygen Silicon Sulfur Tin Zinc Color Shiny or Dull? Metal, nonmetal or metalloid? Group Name (or number if none) Report Page 1 of 3

7 Element Metal, nonmetal or metalloid? Conductive? Does result fit your expectations? Silicon Copper Sulfur Zinc C. Atomic Structure Element Name Protons Neutrons Electrons Mass number Isotope Symbol Li Silver Br Rubidium 87 D. Electronic Structure Element electron configuration number of valence electrons [Ne] 3s 2 3p 1 3 Rb Ag [Kr]5s 2 4d 10 5p 2 S As Report Page 2 of 3

8 Element electron configuration Orbital Diagram [He]2s 2 2p 4 Be P [Kr]5s 2 4d 4 B Report Page 3 of 3