“a-” = “not” “tom-” = “cut” “atom” = “indivisible” Atomic Theory “a-” = “not” “tom-” = “cut” “atom” = “indivisible”

You will need to know the contributions of… Democritus Dalton Rutherford Thomson Millikan Curie Chadwick

You will need to know the contributions of… Democritus– coined the term “atom” (uncuttable) suggested the relationship between the particle and the substance

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 -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 The law of definite proportions The law of multiple proportions

PS The mass of a proton is about the same as the mass of a neutron (an electron is about 1/1800th of that mass) This mass is called an atomic mass unit (1 amu) It is also called a dalton

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, -calculated 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 the process of 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

Protons, neutrons, electrons Name Symbol Mass Charge Location Proton Neutron Electron

Protons, neutrons, electrons Name Symbol Mass Charge Location Proton p 1 amu +1 in nucleus Neutron n 1 amu 0 in nucleus Electron e- 0 amu -1 (about) (about) around nucleus, in electron cloud (about)

Atomic number and mass number Atomic mass number # electrons

Atomic number and mass number Atomic number is the number of protons—this determines the element Atomic mass number = #protons + #neutrons # electrons = # protons, in an uncharged atom

What is an isotope?

What is an isotope? “the same” “place”

What is an isotope? Same Different

What is an isotope? Same Different Element Mass Atomic number Mass number # protons # neutrons # electrons Radioactivity Ion charge Chemical properties (mostly)

Nuclide Notation A nuclide is a nucleus or atom of a specific isotope of an element 39 K 19 This is potassium-39. It has 19 protons (atomic number = 19), making it potassium, and 20 neutrons, making a mass number of 39

How many p, n, e- in each? What is the mass number and atomic number? 3 He 80 Br- 111 Ag+ 2 35 47 59 Fe+2 40 Ca+2 238 Pu 26 20 94

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 (B) (C) (D) 51 V+2 23 14 N-3 7 123 Te-2 52 87 Sr+2 38

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

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

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 Cl-37? Cl-35 has a mass of 34.969 amu/atom The average atomic mass of chlorine is 35.453 amu/atom

How common is S-34? S-32 has a mass of 31.972 amu/atom (less common nuclides are ignored) The average atomic mass of sulfur is 32.060 amu/atom

The greatest conversion of all time! 1 amu X 6.02 x 1023 = 1 gram atom X 6.02 x 1023 mole Avogadro’s number!