Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Atomic Structure Werner Heisenberg http://www.science-class.net/8th_Notes/8th_Notes_MainPage.htm 1. John Dalton (1766-1844) thought that an atom is a sphere of matter that is the same throughout. 2. J.J. Thomson (1856-1940) discovered that all atoms contain electrons, which are tiny, negatively charged particles. Thomson proposed that an atom is a sphere of positive charge. The electrons are mixed uniformly in the sphere. 3. Rutherford (1871-1937) updated the model of the atom. He hypothesized that almost all the mass and all the positive charge of an atom is concentrated in an extremely tiny nucleus at the center of the atom. 4. Bohr (1885-1962) described the atom as a planetary arrangement: electrons orbiting the nucleus. http://www.epa.gov/ 5. Today's model of the atom has a concentrated nucleus containing the protons and neutrons surrounded by a cloud representing where the electrons are likely to be found. a) Protons are in the nucleus (center) of the atom; positive charge b) Neutrons are in the nucleus (center) of the atom; neutral (no charge) c) Electrons move in energy levels outside of the nucleus; negative charge 6. The number of protons in the nucleus of an atom is its atomic number a) The atomic number identifies which element you have. For example, the oxygen atom has atomic number 8, which means that an oxygen atom has 8 protons. 7. In a stable atom, the number of protons equals the number of electrons. a) Atoms that have lost or gained electrons are called ions. b) Atoms that lost electrons form positive ions, e.g. Na+, Ca2+, Al3+ c) Atoms that gained electrons form negative ions, e.g. Cl –, O2–, F – d) Note: To form ions, atoms lose and gain electrons (not protons). 8. The number of protons plus the number of neutrons is the mass number. 9. The atomic weight or atomic mass is the average of the mass numbers of all of the isotopes of an element. 10. Isotopes are atoms of the same element (that have the same number of protons) but that have different numbers of neutrons. The mass of each isotope is equal to the sum of protons and neutrons. 11. Electrons can spin in different directions; scientists cannot tell exactly where an electron is at a given moment or where it is going. They can calculate the probability that an electron will be found in a given space. This is quantum mechanics. CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 1 of 6 12. The electron position as a function of distance from the nucleus is called its energy level, or orbital. The farther the electron is away from the nucleus the higher its energy. a) Each energy level can only hold a certain number of electrons i) The first energy level (1) can hold 2 electrons ii) The second energy level (2) can hold 8 electrons iii) The third energy level (3) can hold up to 18 electrons iv) The fourth energy level (4) can hold up to 32 electrons v) The fifth energy level (5) can hold up to 50 electrons vi) The sixth energy level (6) can hold up to 72 electrons b) Usually, each energy level is completely filled before electrons fill the next level. c) The electrons in the outermost level are called valence electrons. 3 • Valence shell (outermost energy level) 2 • • • 1 • • • • • e- nucleus • • • • • This schematic diagram of an atom indicates that this atom has 6 valence electrons in its outermost energy level (energy level 3). • • 13. An atom's nucleus is held together by the strong nuclear force. If the numbers of neutrons and protons are very different, the nucleus can become unstable and undergo radioactive decay. The Periodic Table The PERIODIC TABLE is an organizational system for elements. Elements are arranged in horizontal rows going from right to left called Periods and columns going up and down called Families or Groups. • Elements in the same period have their valence electrons in the same energy level. For example, elements in period 3 have valence electrons in energy level 3. The start of each new period in the periodic table is the start of a new energy level (it is the start of a new valence shell). Atoms generally get more massive as you move from left to right across a period The atomic radii tend to decrease as you move from left to right across a period Atoms get more massive as you move down a group from top to bottom in the periodic table • Elements in the same family / group have similar properties because they have a similar electron arrangement in their outer shell. CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 2 of 6 PERIODIC TABLE 1A 1 H 1.008 1 2 Period 3 4 5 6 7 1A 3 Li 6.941 11 Na 22.99 19 K 39.10 37 Rb 85.47 55 Cs 132.9 87 Fr (223) 2A 4 Be 9.012 12 Mg 24.30 20 Ca 40.08 38 Sr 87.62 56 Ba 137.3 88 Ra (226) 3 4 5 21 22 23 Sc Ti V 44.96 47.88 50.94 39 40 41 Y Zr Nb 88.91 91.22 92.91 72 73 La-Lu Hf Ta 178.5 180.9 104 105 Ac-Lr Rf Db (261) (262) Lanthanides Actinides 6 7 24 25 Cr Mn 52.00 54.94 42 43 Mo Tc 95.94 (98) 74 75 W Re 183.8 186.2 106 107 Sg Bh (263) (264) 8 26 Fe 55.85 44 Ru 101.1 76 Os 190.2 108 Hs (265) 9 27 Co 58.93 45 Rh 102.9 77 Ir 192.2 109 Mt (268) 10 28 Ni 58.69 46 Pd 106.4 78 Pt 195.1 110 Uun (269) 11 29 Cu 63.55 47 Ag 107.9 79 Au 197.0 111 Uuu (272) 12 30 Zn 65.39 48 Cd 112.4 80 Hg 200.6 112 Uub (269) 3A 5 B 10.81 13 Al 26.98 31 Ga 69.72 49 In 114.8 81 Tl 204.4 4A 6 C 12.01 14 Si 28.09 32 Ge 72.61 50 Sn 118.7 82 Pb 207.2 114 Uuq 5A 7 N 14.01 15 P 30.97 33 As 74.92 51 Sb 121.8 83 Bi 209.0 6A 8 O 16.00 16 S 32.07 34 Se 78.96 52 Te 127.6 84 Po (209) 116 Uuh 7A 9 F 19.00 17 Cl 35.45 35 Br 79.90 53 I 126.9 85 At (210) 8A 2 He 4.003 10 Ne 20.18 18 Ar 39.95 36 Kr 83.80 54 Xe 131.3 86 Rn (222) 118 Uuo 57 58 59 60 La Ce Pr Nd 138.9 140.1 140.9 144.2 61 Pm (145) 62 63 Sm Eu 150.4 152.0 64 Gd 157.2 65 66 67 Tb Dy Ho 158.9 162.5 164.9 68 Er 167.3 69 Tm 168.9 70 Yb 173.0 71 Lu 175.0 89 90 91 92 Ac Th Pa U (227) 232.0 231.0 238.0 93 Np (237) 94 Pu (244) 96 Cm (247) 97 98 Bk Cf (247) (251) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (262) 95 Am (243) 99 Es (252) Metals are on the left hand side of the table (to the left of the metalloids) Non-metals are on the right-hand side of the table (to the right of the metalloids). Metalloids (semi-metals) are between the metals and non-metals (shaded). Group 1A Alkali metals - Elements whose atoms have 1 valence electron; they are very reactive Note: Hydrogen although nominally a member of Group 1A, very rarely exhibits behavior comparable to the alkali metals. Hydrogen is a non-metal. Group 2A Alkaline Earth Metals - Elements whose atoms have 2 valence electrons (2 electrons in the outermost energy level) Group 3A Elements whose atoms have 3 valence electrons Group 4A Elements whose atoms have 4 valence electrons Group 5A Elements whose atoms have 5 valence electrons Group 6A Elements whose atoms have 6 valence electrons Group 7A Halogens - Elements whose atoms have 7 valence electrons Group 8A Noble Gases (also called inert gases) - Elements whose atoms have full outer shells so they are very unreactive. Reference: Devlin Gualtieri http://www.science-class.net/8th_Notes/8th_Notes_MainPage.htm VIDEO: Tom Lehrer’s video on the elements. http://www.privatehand.com/flash/elements.html The video starts as soon as you double click on the connection speed: dial up or broad band. CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 3 of 6 Questions: 1. Consider the fluorine atom, F, which is atomic number 9 in the periodic table. • • • • • 9 F 19.00 9 P+ 10 N • e• Atomic number = number of protons = 9 protons (P+) Atomic Symbol Atomic mass = mass of protons + mass of neutrons Number of neutrons = Atomic mass – Number of protons Number of neutrons = 19 – 9 = 10 neutrons (N) Number of electrons = Number of protons = 9 electrons (e-) • • How many valence electrons does fluorine have? 3 2. Consider the atomic structure of an atom as follows: 2 • • • • • • • e- nucleus • • 1 • • • • • • a) What is the total number of electrons in the atom shown? b) If this diagram represents a neutral atom (no charge), the number of protons (each proton has a +1 charge) equals the number of electrons (each electron has a –1 charge). How many protons does this atom have? c) The number of protons is equal to the atomic number. Find the atomic number of this atom in the periodic table. Identify the element. 3. The sodium atom has the symbol Na. Find sodium in the periodic table. The atomic number for sodium is 11. The atomic number equals the number of protons in the atoms of a given element. The mass of protons and neutrons are very nearly equal to one another. The mass of an electron is 1846 times less than a proton. In the periodic table, the atomic mass of sodium is given to be 22.99. The mass of the electrons is negligible in the atomic mass of an atom. Atomic Mass = Mass of the protons + Mass of the neutrons a) How many protons does a sodium atom have? b) Round up the atomic mass given to a whole number. The number of neutrons equals the atomic mass minus the number of protons. How many neutrons does a sodium atom have? CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 4 of 6 c) On the diagram below, draw the number of electrons (e –), protons (p+) and neutrons (n) for the sodium atom. d) How many valence electrons does sodium have? 4. The chlorine atom has the symbol Cl. Find chlorine in the periodic table. a) How many protons does a chlorine atom have? b) How many neutrons does a chlorine atom have? c) On the diagram below, draw the number of electrons (e –), protons (p+) and neutrons (n) for the chlorine atom. d) How many valence electrons does the chlorine atom have? e) How many electrons does chlorine need to complete its valence shell? 5. When sodium and chlorine react to form the common table salt, NaCl, sodium gives up one electron to form a positive ion with a +1 charge, Na+, and chlorine accepts one electron to form a negative ion with a –1 charge, Cl–. The ions Na+ and Cl– combine in a 1:1 ratio to form ionic bonds in an ionic solid. a) How many valence electrons does the ion Cl– have? b) How many valence electrons does the ion Na+ have? c) In your diagram of the sodium atom in question 3c, circle the valence electron and draw an arrow from this electron to the outer shell of the chlorine atom diagram in question 4c. This is how the electron is transferred to form the ionic bond between Na+ and Cl–. Common table salt, NaCl, is a stable compound because both Na+ and Cl– have a filled valence shell. Note: The atomic mass given in the periodic table is the weighted average mass of the naturally occurring isotopes for a given element. Sodium has only one isotope that occurs in nature. However, chlorine has two naturally occurring isotopes: one isotope has a mass of 35.0 (75.8%), the other isotope has a mass of 37.0 (24.2%). The weighted average mass of these two isotopes is 35.45 as indicated in the periodic table. Thus, the method we are using to determine the number of neutrons by rounding the mass to the nearest whole number is an approximate method. CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 5 of 6 Chemical Bonding Atoms can react with one another to form new substances called compounds. When two or more atoms chemically bond together, the resulting compound is unique both chemically and physically from its parent atoms. But why do atoms react to form compounds? Chemical bonds are formed between atoms because electrons from different atoms interact with each other. G. N. Lewis observed that many elements (in the second and third period of the periodic table) are most stable when they contain eight electrons in their valence shell. He suggested that atoms with fewer than eight valence electrons bond together to share electrons and complete their valence shells. Remember that noble gases (or inert gases) are generally not reactive and exist as stable monatomic gases (single atom gases) at room temperature and pressure. They have the number of electrons they need to be stable as single atoms and therefore rarely form compounds. The halogens in Group 7A are in the column right next to the noble gases in group 8A and need only one electron to end up with the same number of electrons as a noble gas element. For example, the atomic number for chlorine is 17, which means it has 17 protons and 17 electrons. When the chlorine atom gains one electron to form Cl–, it has 18 electrons, the same number of electrons as the noble gas element argon, Ar. Note: Cl– has a minus one charge but the one is usually not shown. The alkali metals in group 1A have only one electron in their valence shell. They lose one electron to end up with the same number of electrons as a noble gas element. For example, the atomic number for sodium is 11, which means it has 11 protons and 11 electrons in the neutral atom. When a sodium atom loses one electron to form Na+ it has 10 electrons which is the same number of electrons as the noble gas element neon, Ne. Cl-1 Na Cl-1 Na Cl-1 Cl-1 +1 + +1 Na sodium metal Na (s) chlorine gas Cl2 (g) table salt NaCl (s) sodium (on the left) loses its one valence electron to chlorine (on the right), Sodium Chloride Crystal Na Cl-1 Na Cl-1 Na Na Cl-1 Na Cl-1 Cl-1 Na Cl-1 Na +1 +1 +1 +1 +1 +1 +1 +1 NaCl Crystal Schematic to form a positively charged sodium ion (left) and a negatively charged chlorine ion (right). Reference: Anthony Carpi http://www.visionlearning.com/library/module_viewer.php?mid=55 CaMSP Science Matters Summer Institute 2007 Petra van Koppen Page 6 of 6