Unit II Atomic Structure

Obj. 1…Daltons Atomic Theory Four postulates (1808)... Four postulates (1808) Atoms of the same element are identical... each element is unique * proton, neutron and electron isotopes exist * Much of this theory is still accepted, Much of this theory is still accepted, with exceptions with 2 exceptions 3. Atoms of different elements can physically mix or chemically combine (compounds). 1. All elements are composed of tiny, indivisible particles called atoms. 4. Chemical rxns. occur when atoms are separated, joined, or rearranged.

Obj. 2…Atomic Scientists J. J. Thomson discovered electrons (e-) in J. J. Thomson discovered electrons (e-) in He passed an electric current through a glass He passed an electric current through a glass tube filled with gas. He discovered that a beam of negative charges He discovered that a beam of negative charges traveled from the cathode (-) to the anode (+).

Obj. 2 cont... E. Goldstein discovered positive particles in atoms E. Goldstein discovered positive particles in atoms in He observed rays traveling in the opposite direction of He observed rays traveling in the opposite direction of cathode rays. These particles were termed protons (p + ) by Ernest These particles were termed protons (p + ) by Ernest Rutherford in His discovery was based on the fact that His discovery was based on the fact that different atoms atomic mass and atomic # (# of protons) were not adding up. James Chaddwick discovered neutrons (n 0 ) James Chaddwick discovered neutrons (n 0 ) in 1932.

Obj. 2 cont... all e- carry exactly one unit of negative charge. all e- carry exactly one unit of negative charge. mass of an e- is 1/1840 the mass of a hydrogen atom (p + ). mass of an e- is 1/1840 the mass of a hydrogen atom (p + ). Robert Millikan furthered Thomsons work by describing Robert Millikan furthered Thomsons work by describing the electron more in depth.

Obj. 3 and 4…The Bohr-Rutherford Model 1. atoms are mostly space. (football arena) Ernest Rutherford conducted the famous gold foil Ernest Rutherford conducted the famous gold foil experiment (1911) which concluded that: 2. atoms have a solid nucleus at the centerwhich contains most of the mass. center which contains most of the mass. This overturned the accepted plum pudding model of the This overturned the accepted plum pudding model of thetime.

Obj. 3 and 4 cont... The Gold Foil Experiment... The Gold Foil Experiment... Stats... Stats... 98% of particles went straight through (expected) 98% of particles went straight through (expected) 2% of particles deflected at large angles 2% of particles deflected at large angles 0.01% of particles deflected straight back (canon balls & tissue!) 0.01% of particles deflected straight back (canon balls & tissue!) (BBs and cream cheese!)

Obj. 3 and 4 cont... The progression of the atom... The progression of the atom... Why dont the (-) e- fall into the (+) nucleus? Why dont the (-) e- fall into the (+) nucleus? Plum Pudding Rutherford Rutherford-Bohr Quantum After Rutherfords findings, Niels Bohr further explained After Rutherfords findings, Niels Bohr further explained the atom by concentrating on the e- (1913). Bohr proposed that the e- travel on concentric Bohr proposed that the e- travel on concentric orbits around the nucleus. Each orbit has a fixed energy (energy level) and e- do not Each orbit has a fixed energy (energy level) and e- do not lose energy.

Obj. 5…Subatomic Particles PROPERTIES OF SUBATOMIC PARTICLES PROPERTIES OF SUBATOMIC PARTICLES PARTICLE SYMBOL ELECTRICAL CHARGE RELATIVE MASS ACTUAL MASS (g) ElectronProton Neutron e- p+p+p+p+ n0n0n0n / x x

Obj. 6…Characteristics of Elements K 19 Potassium atomic # element symbol element name atomic mass

Obj. 6 cont... Atomic #: Atomic #: # of p + in an atom # of p + in an atom identifies element identifies element # p + = # e- in neutral atom # p + = # e- in neutral atom (change atomic # = change of element). ** (+) charge = less e- than p + ** (-) charge = more e- than p + Atomic mass: Atomic mass: mass of the nucleus mass of the nucleus p + + n 0 p + + n 0 units are a.m.u. (atomic mass unit) units are a.m.u. (atomic mass unit) (a.k.a. mass #)

Obj. 7…Atomic Symbols There are two ways to represent elements: There are two ways to represent elements: Symbol Form: Symbol Form: # X # atomic mass (# of p + ) atomic # element symbol # X atomic mass element symbol OR OR Shorthand Form: Shorthand Form: name of element followed by atomic mass. name of element followed by atomic mass. Ex... Ex... Carbon - 14 Carbon - 14 Aluminum - 27 Aluminum - 27 Nitrogen - 14 Nitrogen - 14 You can find mass #, atomic #, # of n 0, and # of e- with You can find mass #, atomic #, # of n 0, and # of e- with either notation!

Obj. 8…Atomic Calculations All mass of the atom is in the nucleus. All mass of the atom is in the nucleus. - only p + and n 0 are in the nucleus. - only p + and n 0 are in the nucleus. - if you know the mass of any atom, you can find the # of n 0. - if you know the mass of any atom, you can find the # of n 0. Ex... Ex P electrical charge on atom electrical charge on atom element = _______________ element = _______________ atomic mass = ___________ atomic mass = ___________ atomic # = ______________ atomic # = ______________ # of p + = _______________ # of n 0 = _______________ # of e - = _______________ Phosphorus 31 a.m.u.s Manganese - 55 Manganese - 55 symbol = ______________ symbol = ______________ atomic mass = __________ atomic mass = __________ atomic # = ____________ atomic # = ____________ # of p + = ______________ # of n 0 = ______________ # of e - = ______________ Mn 55 a.m.u.s if you know the # of n 0 and the # of p+, you can find the - if you know the # of n 0 and the # of p+, you can find themass.

Obj. 9…Isotopes - different # of n 0 !!! - different # of n 0 !!! Three isotopes of Carbon: Three isotopes of Carbon: Carbon - 14 Carbon - 14 Carbon - 12 Carbon - 12 Carbon - 13 Carbon - 13 (6p +, 6n 0 ) (6p +, 6n 0 ) (6p +, 7n 0 ) (6p +, 7n 0 ) (6p +, 8n 0 ) (6p +, 8n 0 ) element of life element of life extremely rare extremely rare radioactive…carbon dating radioactive…carbon dating Note: atomic # will NEVER change in isotopes… Note: atomic # will NEVER change in isotopes… only mass and # of n 0 do! Which of the following are isotopes of the same element? Which of the following are isotopes of the same element? 22 22X X X Neon - 20 Neon - 20 Neon - 22 Neon - 22 Fluorine - 20 Fluorine - 20 Isotopes: atoms of the same element with different atomic Isotopes: atoms of the same element with different atomic masses.

Obj. 10…Average Mass of Isotopes Isotopes are naturally occurring. Isotopes are naturally occurring. The mass # of an element (periodic table) is the weighted The mass # of an element (periodic table) is the weighted avg. of allisotopes that exist in nature. avg. of all isotopes that exist in nature. - abundance of isotope is just as important as mass! - abundance of isotope is just as important as mass! Ex... Ex... Natural copper (Cu) consists of 2 isotopes... Natural copper (Cu) consists of 2 isotopes... Copper - 63 (mass = g/mole) Copper - 63 (mass = g/mole) Copper - 65 (mass = g/mole) Copper - 65 (mass = g/mole) 69% 69% 31% 31% To calculate avg. mass... To calculate avg. mass... mass x abundance for each isotope Step 1 : Step 2 : add the two values from step 1 together x.69 = x.31 = g/mole

Obj. 10 cont... Ex... Ex... Three isotopes of Oxygen: Three isotopes of Oxygen: Oxygen - 18 Oxygen - 18 Oxygen - 16 Oxygen - 16 Oxygen - 17 Oxygen - 17 The avg. mass (from P.T.) is closest to 16, therefore, The avg. mass (from P.T.) is closest to 16, therefore, Oxygen-16 is the isotope that is most abundant in nature % 0.037% 0.204% The average mass of an element is closest to the isotope The average mass of an element is closest to the isotope that is mostplentiful in nature. that is most plentiful in nature.