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Atomic Theory “Atom” means uncuttable. It isn’t. --but it is the smallest particle of an element Early models of the atom • Classical model • “Plum pudding” model • Solar system model You need to know these people • • • • • • • Democritus Dalton Rutherford Millikan Thomson Chadwick? Curie You will need to know the contributions of… • Democritus—first used the term “atom” • Considered four “elements”: earth, air, fire and water (it could translate as “characteristics”) • The physical shape of the “atom” gave substances their physical properties. • “Atoms” are not changed in mixtures You will need to know the contributions of… • Dalton—modern atomic theory • -all matter is made of atoms • -atoms of one element are identical, atoms of different elements are different • -atoms form compounds in simple whole number ratios • -chemical reactions are rearrangements of atoms, the atoms are not changed • -compounds with different ratios of atoms are different compounds You will need to know the contributions of… • Dalton—modern atomic theory The law of • -all matter is made of atoms definite • -atoms of one element are identical, atoms of proportions different elements are different • -atoms form compounds in simple whole number ratios The law of • -chemical reactions are rearrangements of multiple atoms, the atoms are not changed proportions • -compounds with different ratios of atoms are different compounds The mass of a proton=1 dalton • It’s about the same mass as a neutron (an electron is about 1/1800th of that mass) • ~1.7 x 10-24g It’s also called an atomic mass unit (1amu) You will need to know the contributions of… • Rutherford-Gold foil experiment -showed atom is mainly empty space -mass and (+) charge in the center You will need to know the contributions of… • Thomson— cathode “rays” • = stream of electrons • He calculated the charge/mass ratio of electron You will need to know the contributions of… • Millikan—oil drop experiment •determined the charge (& therefore the mass) of an electron You will need to know the contributions of… • Curie— • -described radioactive decay of atoms You will need to know the contributions of… • Chadwick— • -discovered neutrons Cloud chamber— the straight track shows that it has no charge 19 39.0983 K Potassium Atomic Number = number of protons Name 19 39.0983 K Potassium Average atomic mass, in amu/atom Symbol Atomic number and mass number Atomic number Atomic mass number # electrons Atomic number and mass number Atomic number is the number of protons— determines the element Atomic mass number = #protons + #neutrons # electrons = # protons, in an atom Atomic number and mass number Atomic number is the number of protons— determines the element Atomic mass number = #protons + #neutrons # electrons = # protons, in an atom An atom gains, loses, or shares electrons to form chemical bonds Protons, neutrons, electrons Name Proton Neutron Electron Symbol Mass Charge Location Protons, neutrons, electrons Name Symbol Mass Charge Location (about) Proton p 1 amu +1 in nucleus 0 in nucleus (about) Neutron n 1 amu (about) Electron e- 0 amu -1 around nucleus, in electron cloud Name Symbol Atomic Atomic # p #n Number Mass (most Number likely) Sulfur K 20 17 # e- Name Symbol Atomic Atomic # p # n # eNumber Mass (most Number likely) Sulfur S 16 32 16 16 16 Potassium Calcium K 19 39 19 20 19 Ca 20 40 20 20 20 Chlorine Cl 17 35 17 18 17 What is an isotope? What is an isotope? “the same” “place” Isotope (or nuclide) Notation 39 19 K This is potassium-39 atomic number = 19 19 protons, making it potassium, 20 neutrons, mass number of 39 Isotope (or nuclide) Notation 39 19 K 42 19 K This is potassium-42 atomic number = 19 19 protons, making it potassium, 23 neutrons, mass number of 42 What is an isotope? Same Different What is an isotope? Same Element Atomic number # protons # electrons Ion charge Chemical properties (mostly) Different Mass Mass number # neutrons Radioactivity What is the atomic number and mass number? Proton Neutron Electron (A) 23 28 21 (B) 7 7 10 (C) 52 71 54 (D) 38 49 36 What is the atomic number and These aren’t mass number?atoms! Proton Neutron Electron (A) 23 28 21 (B) 7 7 10 (C) 52 71 54 (D) 38 49 36 Write the nuclide designation Proton Neutron Electron (A) 23 28 21 (B) 7 7 10 (C) 52 71 54 (D) 38 49 36 Write the nuclide designation (A) (B) 51 23 14 7 (C) (D) +2 V -3 N 123 52 87 -2 Te +2 Sr 38 \What is the mass number and atomic number? 3 2 He 59 26 +2 Fe 80 Br 35 - 111 47 + Ag 40 238 20 94 +2 Ca Pu How many p, n, e- in each? 3 2 He 59 26 +2 Fe 80 Br 35 - 111 47 + Ag 40 238 20 94 +2 Ca Pu Average atomic mass • --A weighted average of the naturally occurring isotopes Average atomic mass • --A weighted average of the naturally occurring isotopes Ex: 99.63% N-14 (mass=14.003 amu/atom) .37% N-15 (mass=15.000 amu/atom) Average atomic mass • --A weighted average of the naturally occurring isotopes Ex: 99.63% N-14 (mass=14.003 amu/atom) .37% N-15 (mass=15.000 amu/atom) Avg= (.9963x14.003) +(.0037x15.000)= Average atomic mass • --A weighted average of the naturally occurring isotopes Ex: 99.63% N-14 (mass=14.003 amu/atom) .37% N-15 (mass=15.000 amu/atom) Avg= (.9963x14.003) +(.0037x15.000)= =13.951 + .056 = 14.007 amu / atom Average atomic mass • What is the average atomic mass of carbon: • 98.89% C-12 (12.000 amu/atom) • 1.11% C-13 (13.003 amu/atom) Average atomic mass • What is the average atomic mass of carbon: • 98.89% C-12 (12.000 amu/atom) • 1.11% C-13 (13.003 amu/atom) 12.011 amu/atom How common is S-32? • S-32 has a mass of 31.972 amu/atom • S-34 has a mass of 33.967 amu/atom • (less common nuclides are ignored) • The average atomic mass of sulfur is 32.060 amu/atom A) 5% B) 35% C) 65% D) 95% How common is Cl-37? • Cl-35 has a mass of 34.969 amu/atom • Cl-37 has a mass of 36.966 amu/atom • The average atomic mass of chlorine is 35.453 amu/atom A) 25% B) 50% C) 75% D)100% The Periodic Table of Elements The Periodic Table of Elements • Dmitry Mendeleev (Дми́трий Ива́нович Менделе́ев) • Noticed physical and chemical properties repeated every seven elements (by atomic mass) • Predicted the discovery of gallium and germanium The Periodic Table of Elements • Dmitry Mendeleev (Дми́трий Ива́нович Менделе́ев) • Noticed physical and chemical properties repeated every seven elements (by atomic mass) • Predicted the discovery of gallium and germanium Periodic properties seen by Mendeleev: He predicted the properties of unknown elements, later discovered Know these features: Period Series Group Family Alkali metals Alkaline earth metals Transition elements Representative elements Halogens Noble gasses Lanthanide series Actinide series The Periodic Table of Elements A period A series A group or family The alkali metals The alkaline earth metals Transition elements Representative elements The Halogens (salt-makers) The Noble Gasses The Periodic Table of Elements Boron Family Carbon Family Nitrogen Family Oxygen Family The Periodic Table of Elements Lanthanide series Actinide series The Periodic Table of Elements