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Periodic Table An atom refresher • Matter is anything that takes up space and has mass. • All matter is made of atoms • Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses. • Who contributed to the atomic theory from ancient Greece to modern day? Scientist that contributed to the Atomic Theory include: • Democritus – “Atomos” • JJ Thomson – cathode ray tube, found electrons, Plum Pudding model • Ernest Rutherford – gold foil expt., found nucleus as a positive center • Neils Bohr – Bohr model with orbitals for electrons around the nucleus, like a planetary system • Schrodinger – said e- act as particles • Chadwick – found neutrons • Heisenburg – pulled together all & said there is an electron cloud model, quantum Atom • An atom has three parts: • Proton = positive • Neutron = no charge • Electron = negative • The proton & neutron are found in the center of the atom, a place called the nucleus. • The electrons orbit the nucleus. What are elements? • Elements are the alphabet to the language of molecules. • To make compounds, you must have elements. • Elements are made of atoms. While the atoms may have different weights and organization, they are all built in the same way. More about Elements.. • Elements are the building blocks of all matter. • The periodic table is a list of all of the elements that can build matter. It’s a little like the alphabet of chemistry. • The periodic table tells us several things… Families or groups Alkali Metals Alakaline Earth Metals Transition Metals Halogens Noble or Inert Gases Lanthinide Series Actinide Series What 2 main categories are on the periodic table? On your periodic table: • Number the TALL Columns 1-8 because these are called “representative elements” that the tall column number is the same for how many valence electrons exist on the outer most orbital Periodic Table Atomic Number: Number of protons and it is also the same number of electrons in the element. Symbol: An abbreviation for the element. Elements Name Atomic Mass/Weight: Number of protons + neutrons that exist in the nucleus. 8 O Oxygen 16 Using your periodic table • Find the following using your periodic table: Symbol Na Al Cr Bi Ra Name Mass # Atomic # protons electrons What is an isotope? • Isotopes are two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei • Examples: C-12 U-235 C-13 U-236 C-14 U-238 1. How many p+, e-, n0 exist in each isotope? 2. What is the element when it is 41 19 X? Shorthand Notation: Mass number Symbol Atomic number 35Cl 17 1. Write the shorthand notation for Al Cr Bi Ra 2. What do you use to tell the identity of an element? 3. What changes to result in a charge on an element? 4. What is an element with a charge called? ION is a charged element 1.Ions are a result of electrons being ________. 2. A positive charged element has ______ electrons & is called a ______. 3. A negative charged element has _____ electrons & is called a _____. 4. Draw the Bohr models of Na + Cl NaCl and show how electrons are transferred. Which part of the reaction is a cation?______ Which is an anion?_____ 5. Which element gives up electrons when lithium combines with fluorine to make lithium fluoride: Li + F LiF Li+1 + F-1 LiF Atom Models • There are two models of the atoms we will be using in class. • Bohr Model (orbitals around nucleus & show valence electrons only in outer orbital) • Lewis Dot Structure (only uses valence electrons around the symbol & we will do these at a later time) Bohr Model • The Bohr Model shows all of the particles in the atom. • In the center is the nucleus. • In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e. e Electrons have special rules…. • You can’t just shove all of the electrons into the first orbit of an element. • Electrons live in something called shells or energy levels also referred to as orbitals. • Only so many can be in any certain shell. • The electrons in the outer most shell of any element are called valance electrons. Nucleus 1st shell 2nd shell 3rd shell 4th shell – if valence orbital then it can only hold a maximum of 8 electrons NOTE: Only when there is another orbital on the outside can the 3rd shell hold up to 18 e-, otherwise if this is the outermost orbital then it can only hold 8 electrons to obey the octet rule! So let’s try it…. • Draw the Bohr model for lithium: 3 Li Lithium 7 QUIZ on Friday, I can: (if absent be ready to take on Tuesday during Eagle Time) • Interpret the arrangement of the Periodic Table, including groups names and periods, for orbitals & number of valence e-, & to know that properties are similar for elements in a group • Describe the structure of atoms, including the masses, electrical charges, and locations of protons, neutrons, and electrons • Identify that protons determine an elements identity and valence electrons determine its chemical properties, including reactivity • Describe the historical development of atomic theory & periodic table – who did what. On the Quiz, I can: • Determine the number of protons, neutrons, electrons, and charge of a neutral, ion, or isotopic element by using isotope notation. Who did what? (copy & Match them up) • I used the Gold Foil Experiment to discovered + • Dimitri Mendeleev charged nucleus & my model • Democritus & the “planetary system” Aristotle • I was the first to call the atom • Niels Bohr as atomos • I worked with organizing the • John Dalton periodic table using atomic numbers. • I discovered the electron using a cathode tube & my atom model is called the “plum pudding” model • Henry Moseley • Ernest Rutherford • J.J. Thomson Continue with Who did what? • I organized the 1st periodic table using atomic masses. • Dimitri Mendeleev • Democritus & Aristotle • My atomic model helped • describe the orbits of electrons, has been called • the planetary model & is • still used today. • • I believed that atoms could not be broken down • Niels Bohr John Dalton Henry Moseley Ernest Rutherford J.J. Thomson REVIEW the Periodic table: 1.How many electrons and protons are contained in an atom of each of the following elements? • a. arsenic d. molibdenum • b. gold e. polonium • c. fluorine f. barium 2. Identify the atom containing the following number of electrons (not ions). • a. 34 d. 61 • b. 5 e. 94 • c. 31 3. Identify the atom containing the following number of protons. • a. 74 d. 70 • b. 20 e. 93 • c. 49 4. Add the number of orbitals and valence electrons that exist on the elements in question 3. 5. Atoms of which element contain 18 protons and 18 electrons? 6. Describe the subatomic particles comprising an isotope of zirconium-94. 7. An atom of a certain element has a mass number of 112 and is known to contain 64 neutrons. Identify the atom and determine the number of electrons and protons the atom contains. 8. A neutral atom has 78 electrons and a mass number of 198. Identify the atom and determine the number of protons and neutrons in its nucleus. How to solve for ATOMIC MASS: • Atomic mass Scientists have established a standard for the measurement of atomic mass by assigning the carbon-12 atom a mass of 12 atomic mass units (amu). Thus, 1 amu is equal to 1/12 the mass of a carbon-12 atom. • The number at the bottom of each square in the periodic table is the atomic mass of that element in amu. A scan of the periodic table will immediately tell you that the atomic masses of many elements are not whole numbers. The reason for this is that many elements occur in nature as a mixture of isotopes—isotopes with different masses. ATOMIC MASS • The atomic mass of an element given in the table is a weighted average of the atomic masses of the naturally occurring isotopes of the element. This weighted average takes into account the mass and abundance of each of the isotopes. Example Problem: Calculating Atomic Mass Copper exists as a mixture of two isotopes. • Cu-63 makes up 69.17% of copper atoms with an atomic mass of Cu-63 is 62.930 amu • Cu-65 constitutes the remaining 30.83% of copper atoms with an atomic mass of 64.928 amu STEPS to SOLVE by: 1)Put the % value into a decimal value 2)Mass contribution = mass of isotope X abundance of isotope put in a decimal value 3)The average atomic mass or amu of the element is the sum of the mass contributions of each isotope Review “average atomic mass” Ex. Sample of cesium is 75% of 133 amu, 20% of 132 amu, and 5% of 134, what is the average atomic mass? Answer: .75 X 133 = 99.75 .20 X 132 = 26.4 .05 X 134 = _6.7__ Total + 132.85 amu or average atomic mass 127 126 128 1. 80% I, 17% I, 3% I 2. 50% 197Au, 50% 198Au 3. 15% 55Fe, 85% 56Fe 4. 99% 1H, 0.8% 2H, 0.2% 3H Review “average atomic mass” 5. The following table shows the five isotopes of germanium found in nature, the abundance of each isotope, and the atomic mass of each isotope. Calculate the average atomic mass of germanium. • Isotope Abundance (%) Atomic Mass (amu) • Germanium-70 21.23 % 69.924 • Germanium-72 27.66 % 71.922 • Germanium-73 7.73 % 72.923 • Germanium-74 35.94 % 73.921 • Germanium-76 7.44 % 75.921 6. Gallium occurs in nature as a mixture of two isotopes. They are Ga-69 with a 60.108% abundance and a mass of 68.926 amu and Ga-71 with a 39.892% abundance and an atomic mass of 70.925. Calculate the atomic mass of gallium. 7. The atomic mass of bromine given in the periodic table is 79.904 amu, which is very close to 80 amu. Use a reference book to find the percent of Br-80 in naturally occurring bromine. Explain the value of the atomic mass of bromine from the data you find. 8. The element chlorine occurs in nature as a mixture of two isotopes. Chlorine-35 has an atomic mass of 34.969 amu and makes up 75.77% of chlorine atoms. Chlorine-37 atoms make up the remaining 24.23% of all chlorine. Use the average atomic mass of chlorine from the periodic table to calculate the atomic mass of Cl-37 atoms.