Unit 3 2 structure of the atom
- 1. Counting Protons, Neutrons, and Electrons in Atoms
- 2. Purpose • Matter is made up of atoms, so it is very important to understand what an atom is and the difference between different atoms. In this lesson, we briefly discuss the composition of an atom and learn how to identify atoms, learn the differences between atoms of the same element and the differences between atoms of different elements. Additionally, we learn how to use the periodic table to determine some of this information.
- 3. An atom is made up of 3 particles • Proton – Positively charged particle – In the nucleus – Symbol: p+ • Neutron – Uncharged particle – In the nucleus – Symbol: n0 • Electron – Negatively charged particles – Outside the nucleus – Much lighter than protons and neutrons – approximately 1/2000th the mass of protons and neutrons – Symbol: e-
- 4. Structure of an atom – protons and neutrons in the nucleus, electrons outside the nucleus + + + + - - - - + - proton neutron electronBeryllium atom Note: This is not to scale – electrons are considerably smaller than protons and neutrons and the nucleus is quite a bit smaller than the overall size of the atom.
- 5. The type of atom is determined by the number of protons. • Any atom with 4 protons is a beryllium atom. • Any atom with 6 protons is a carbon atom • The periodic table shows the names and symbols assigned to all known atoms and is organized based on the number of protons each atom contains. • The number of protons is also called the atomic number (Z)
- 6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 57 58 59 60 61 62 63 64 65 66 67 68 69 70 lanthanides (rare earth metals) 89 90 91 92 93 94 95 96 97 98 99 100 101 102 actinides Lu Hf Ta Y Zr 52.00 Mn manganese 54.94 Cr chromium V vanadium 157.3 gadoliniumneodymium 138.9 144.2 145 150.4 152.0 266262 261 227 262 americiumactinium lanthanum Ac cerium praseodymium berkelium CmTh Pa Pu Am 259247 247 251 252 257 258 fermium mendelevium 237 239 243 curium Np No 232.0 231.0 238.0 MdCf EsU neptunium plutoniumthorium protactinium uranium nobelium Bk californiumeinsteinium Fm Er erbiumdysprosium La Ce Pr Nd Pm Sm Gd 272 285 roentgentiumununbium promethium Yb ytterbium 173.0158.9 162.5 DyTb terbium 164.9 167.3 Tm thulium 168.9 Ho holmium Uub lawrenciumrutherfordiumdubnium seaborgium bohrium hassium samarium europium Eu meitneriumdarmstadtium 264 277 268 281 Lr Rf Db Sg Bh Hs Mt Ds Rg iridium platinum gold mercury 175.0 178.5 180.9 183.8 186.2 190.2 lutetium hafnium tantalum tungsten rhenium osmium 192.2 195.1 197.0 200.6 technetium ruthenium rhodium palladium 98 101.1 102.9 106.4 yttrium zirconium Os Ir Pt Au Hg 88.91 91.22 92.91 95.94 107.9 112.4 W ununtriumununquadium Mo Ag CdTc Ru Rh Pd molybdenum Tl Pb 106 107 108 109 110 111 112 113 114 silver cadmium Re 284 289 288 292 294 astatine radon 210 222 ununpentiumununhexium Uup Uuh ununoctium 204.4 207.2 209.0 209 UuoUut Uuq Po thallium lead bismuth polonium At Rn Sb Te I Xe 126.9 131.3 antimony tellurium iodine xenon 69.72 72.64 74.92 78.96 germanium 79.90 83.80 114.8 118.7 121.8 127.6 arsenic selenium indium tin In Sn 30.97 As Kr 39.95 bromine 32.07 35.45 Ar aluminum silicon phosphorus sulfur chlorine argon Si 28.09 BrSe krypton Ga Ge P S Cl 50.94 Nb niobium Ti titanium 47.87 Cu copper 63.55 Zn zinc 65.41 iron 55.85 Co cobalt 58.93 Ni nickel 58.69 gallium N nitrogen 14.01 Ne neon 20.18 O oxygen 16.00 F fluorine 19.00 boron 10.81 C carbon 12.01 132.9 137.3 sodium Fe 5 V B 22.99 24.31 Al 26.98 Ca 40.08 Sc scandium 44.96 rubidium strontium 85.47 87.62 9.012 K 103 104 105 4.003 Li H hydrogen 1.008 13 III A 14 IV A Mg 6 VI B 7 VII B 8 VIII B 12 II B 9 VIII B 10 VIII B 11 I B 15 V A 16 VI A Be B 4 5 potassium calcium 39.10 18 VIII A 17 VII A He helium Period 1 2 3 1 I A lithium Na 6.941 Rb Sr 2 II A 3 III B 4 IV Bmagnesium beryllium 6 7 226 140.1 140.9 Fr Cs Ba cesium barium Ra francium radium 223 Bi 115 116 118 4 9.012 Be beryllium Atomic Number gives the number of protons Symbol Name
- 7. Pause and Practice • Use the periodic table to complete the table below: Element Symbol Element Name Atomic Number Number of protons H Hydrogen 1 1 Mg 12 Iron 26 10 K
- 8. Pause and Practice - Answers • Use the periodic table to complete the table below: Element Symbol Element Name Atomic Number Number of protons H Hydrogen 1 1 Mg Magnesium 12 12 Fe Iron 26 26 Ne Neon 10 10 K Potassium 19 19
- 9. A note about periodic table symbols. • Symbols can be one or two letters – One letter symbols are always capitalized • Hydrogen = H • Oxygen = O – Two letter symbols always have the first letter capitalized and the second letter lowercase • Helium = He • Calcium = Ca
- 10. Symbols you should know – memorize them! • The first 20 element symbols – Hydrogen = H – Helium = He – Lithium = Li – Beryllium = Be – Boron = B – Carbon = C – Nitrogen = N – Oxygen = O – Fluorine = F – Neon = Ne – Sodium = Na – Magnesium = Mg – Aluminum = Al – Silicon = Si – Phosphorus = P – Sulfur = S – Chlorine = Cl – Argon = Ar – Potassium = K – Calcium = Ca • Some other common elements to know – Copper = Cu – Iron = Fe – Lead = Pb – Silver = Ag – Zinc = Zn – Tin = Sn – Mercury = Hg – Bromine = Br – Iodine = I
- 11. The following are the symbols that are missed most often. Pay particular attention to these. • Sodium, silicon, and sulfur – Sodium = Na – Silicon = Si – Sulfur = S • Phosphorus and Potassium – Phosphorus = P – Potassium = K • Metals with symbols derived from other languages. – Copper = Cu – Iron = Fe – Lead = Pb – Silver = Ag – Tin = Sn – Mercury = Hg
- 12. Suggestion • Make a set of flash cards with the name of the element on one side and their symbol on the other for the elements that you have been asked to learn.
- 13. The periodic table tells us how many protons are in every atom. What about electrons and neutrons? • Electrons – For a neutral atom, the number of electrons is the same as the number of protons so it can be determined by looking at the atomic number on the periodic table. • Neutrons – One cannot look at the periodic table and determine the number of neutrons in an atom. – To know neutrons, you must be given the mass number
- 14. Mass number and number of neutrons • Mass number (Z) – The mass number is the total number of protons plus neutrons. Z = #p+ + #n0 – Mass numbers must be given to you, or you must be told the number of neutrons in the atom. • The reason for this is that while a neutral atom of carbon will always have 6 protons and 6 electrons, it can have 6, 7, or 8 neutrons.
- 15. Isotopes are atoms of an element that differ in the number of neutrons they contain. • All carbon atoms have 6 protons – Most carbon atoms have 6 neutrons and are named carbon-12 – Some carbon atoms have 7 neutrons and are named carbon-13 – A few carbon atoms have 8 neutrons and are named carbon-14 • The number after the name is the mass number, which represents the sum of the protons and neutrons
- 16. Pause and Practice • An atom has 19 protons and 21 neutrons. What is its mass number? What is its name? • An atom has a mass number of 37 and contains 17 protons. What is the name of the atom, and how many neutrons does it contain?
- 17. Pause and Practice Answers • An atom has 19 protons and 21 neutrons. What is its mass number? What is its name? – Mass number: 40 – Name: potassium-40 • An atom has a mass number of 37 and contains 17 protons. What is the name of the atom, and how many neutrons does it contain? – Name: chlorine-37 – Number of neutrons: 20
- 18. Misconception Alert • You cannot get mass numbers off the periodic table. • The mass shown on the periodic table will be discussed in a later unit. In short, it is the average mass of all the isotopes of that element – it does not represent any particular atom. • For example, if we asked how many protons and neutrons are in a chlorine atom, you would look at the periodic table and see that it has an atomic number of 17. It therefore has 17 protons. You cannot answer how many neutrons without being told more information.
- 19. We can show atomic number and mass number with the symbols • Carbon-12 has 6 protons, 6 neutrons, and a mass number of 12. We can represent it with the following symbol: 6 12 𝐶 • When writing symbols this way, the mass number(A) goes on the upper left and the atomic number(Z) goes on the lower left of the symbol(X). 𝑍 𝐴 𝑋
- 20. Pause and Practice - Fill in the table Complete Symbol Name Number of protons Number of neutrons Number of electrons Atomic Number Mass Number 6 12 𝐶 Carbon-12 6 6 6 6 12 Hydrogen-1 16 20 16 7 15 20 46 𝐶𝑎
- 21. Pause and Practice Answers Complete Symbol Name Number of protons Number of neutrons Number of electrons Atomic Number Mass Number 6 12 𝐶 Carbon-12 6 6 6 6 12 1 1 𝐻 Hydrogen-1 1 0 1 1 1 16 36 𝑆 Sulfur-36 16 20 16 16 36 7 15 𝑁 Nitrogen-15 7 8 7 7 15 20 46 𝐶𝑎 Calcium-46 20 26 20 20 46