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HOMEWORK: For next Monday Sept 9th CONSTRUCT BY HAND PERIODIC TABLE ON CARTULINAOF 21.5 x 28 cms And Write about ANY of the families of the ELEMENTS Only Symbols, Atomic number and atomic weight Bohr model In atomic physics, the Bohr model, introduced by Niels Bohr in 1913, depicts the atom as small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. After the cubic model (1902), the plumpudding model (1904), the Saturnian model (1904), and the Rutherford model (1911) came the Rutherford–Bohr model or just Bohr model for short (1913). The improvement to the Rutherford model is mostly a quantum physical interpretation of it. The Bohr model has been superseded, but the quantum theory remains sound Amu: Atomic mass unit U:1 g /60..22x10(22) mol(-1) Avogadro=Number of atoms or molecules in one mole 1. Subatomic Particles Particle Electrons Symbol (table O) e 0e -1 0β -1 Protons Neutrons Charge Mass (amu) Location Within atom structure Negative (-1) 1/Avogardos 0 amu Outside nucleus ( in various energy levels) p 1p 1 1H 1 Positive (+1) 1 amu Nucleus n Neutral (0) Nucleus 1n 0 1 amu Special notes on subatomic particles In a neutral atom # of protons=#of electrons. Atoms are electrically neutral. If the number of protons does not equal the number of electrons you have a charged atom known as an ion. # protons > # electrons forms a + ion (cation) # electrons > # protons forms a – ion (anion) The charge on the nucleus is positive. Most of the mass of an atom is in nucleus. 1. Atomic Number (z) 1913—Henry Mosley (Untroduced the concept) Is used to identify an atom Indicates the number of protons In a neutral atoms also gives the number of electrons Also called the Nuclear Charge 3. Mass Number (A) Total number of protons and neutrons in the nucleus of an atom. (nucleons) Notation: AXZ Mass # = #protons + # neutrons # neutrons = Mass # - # protons 36=p+ and e no=48 Exercise: *Mass # = #protons + # neutrons * protons= Num. Electrons *# neutrons = Mass # - # protons Sample Atom Notation Protons (atomic #) Neutrons (mass #atomic #) Electrons(s ame as atomic#) Carbon-12 C-12 12C 6 6 12-6=6 6 Chlorine-35 Cl-35 35Cl 17 17 35-17=18 17 Chlorine-37 Cl-37 37Cl 17 17 37-17=20 17 Neon-20 Ne20 20Ne 10 10 20-10=10 10 *ATOMIC MASS Oxygen Atom Structure Determine the # of protons, neutrons, and electrons for these added examples: 19F9 9 protons 19-9=10 neutrons 9 electrons 19F9-1 -1 Negatively charged 9 protons 10 neutrons 10 electrons 24Mg12 12 protons 24-12=12 neutrons 12 electrons 24Mg12+2 Positively Charged 12 protons 12 neutrons 10 electrons 1. Isotopes Thomson (1912) found 2 types of neon atoms and Soddy (1910) found 2 types of uranium atoms. 2 elements that have the same atomic number but different mass numbers Based on atomic structure: 2 elements that have the same number of protons but different number of neutrons. For example: Cl-35 and Cl-37 Isotopes are not random. Isotopes are formed based on their stability. The more chemically stable an isotope is the higher abundance it will have. Some isotopes are radioactive and are therefore described as radioisotopes For example 14Carbon is a radioactive isotope of carbon whereas 13Carbon are stable isotopes therefore is in abundance over 14Carbon. Carbon Atom Used for radiocarbon dating Carbon 14 Isotope 5. Atomic Mass (Different than Mass NUMBER?) Decimal number (Explain) Average of all the naturally occurring isotopes for a particular element If you round the atomic mass it gives you the mass number for the most common isotope. Unit is amu (atomic mass unit) 1 amu is 1/12 the mass of C-12 Gram atomic mass= amu but in grams IF HYDROGEN ATOM STRUCTURE IS Neutron?: Try the following: 1. Determine the number of protons, neutrons, and electrons for the following isotopes of hydrogen: H2;H3 Solution: Hydrogen-2 (deuterium) 2H1 Hydrogen-3 (tritium) 3H1 1p,1n,1e 1p,2n,1e 1. Naturally occurring chlorine consists of 75% Cl-35 and 25% Cl-37. Find the average atomic mass. .75(35) + .25(37)= 35.50 amu or 75(35) + 25(37) =35.50 amu 100 3. Calculate the atomic mass of an element with isotope A occurring 70.0% of the time with a mass of 13.0 amu and isotope B occurring 30.0% of the time with a mass of 15.0 amu. .70 (13.0) +.30 (15.0) =13.6 amu 1. An element X has three isotopes X-30 has a 50.0% abundance, X-28 has a 30.0% abundance and X-31 has a 20.0% abundance. .500(30) + .300(28) + .200 (31) = 29.6 amu 5. There are two isotopes of element Z, 60.0% of the atoms have a mass of 58.0 amu and 40.0% have a mass of 57.0 amu. Calculate theatomic mass of element Z. .600(58.0) + .400(57) = 57.6 amu