Chapter 5 Atomic Structure and the Periodic Table

Just How Small is an Atom? You don’t need to write. A penny contains about 2.4 × atoms. A speck 0.1 mm in diameter (about half the size of a period at the end of the sentence) requires one million atoms. It would require a million atoms, edge to edge, to match the thickness of a page of paper.

History of the Development of Atomic Models A. Democritus (400 B.C.)  1 st suggested matter is made of atoms  atom- means “indivisible”

John Dalton You don’t need to write. John Dalton ( ), was an English schoolteacher. John Dalton ( ), was an English schoolteacher. Performed experiments to test his atomic theory. Performed experiments to test his atomic theory. Formulated hypothesis and theories to explain his observations. Formulated hypothesis and theories to explain his observations.

History of the Development of Atomic Models B. Dalton ( ) 1. All elements are composed of tiny indivisible particles called atoms  Dalton’s Atomic Theory Is this still true? YES

Dalton’s Atomic Theory 2. Atoms of same element are identical. The atoms of any one element are different from those of any other element. Is this still true?  atoms of the same element can have different masses (isotopes)

Dalton’s Atomic Theory 3. Atoms form compounds by combining in whole number ratios Is this still true?  YES: Law of Definite Proportions

Dalton’s Atomic Theory Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element can never change into another element. No, These changes CAN occur in nuclear reactions! Is this still true?

Structure of the Atom  Nucleus: –contains protons and neutrons –takes up very little space  Electron Cloud: -contains electrons -takes up most of space

Discovery of Nucleus C. Rutherford ( ) discovered the nucleus by shooting alpha particles (have positive charge) at a very thin piece of gold foil –he predicted that the particles would go right through the foil at some small angle

Discovery of Nucleus

some particles (1/8000) bounced back from the foil some particles (1/8000) bounced back from the foil this meant there must be a “powerful force” in the foil to hit particle back this meant there must be a “powerful force” in the foil to hit particle back Predicted ResultsActual Results

Subatomic Particles D. J.J. Thomson ( ) – discovered electrons in atoms; his model was of a positive sphere with e - embedded in it. Milliken ( ) found the mass of the electron E. Milliken ( ) found the mass of the electron F. Goldstein found protons in 1886 G. Chadwick ( ) found the neutron

Discovery of Electron resulted from scientists passing electric current through gases to test conductivity resulted from scientists passing electric current through gases to test conductivity used cathode-ray tubes used cathode-ray tubes noticed that when current was passed through a glow (or “ray”) was produced noticed that when current was passed through a glow (or “ray”) was produced You don’t need to write.

Discovery of Electron This led scientists to believe there were negatively charged particles inside the cathode ray

Properties of Subatomic Particles ParticleSymbol Relative electrical charge Relative mass Actual mass (g) Electrone-e- 1-1/ × Protonp+p × Neutronn0n ×

How to find: A. A. # of protons = atomic number B. B. # of neutrons = rounded mass # – atomic # C. C. # of electrons = # of protons

1. Chemical Symbols a)Printed: 1 st letter capital, 2 nd letter lower case b)Represents one atom of an element Fe ClB

2. Important principles about the atom a)All atoms are electrically neutral (p + = e - ) b)Nearly all mass is in the nucleus c)Lots of space between nucleus and e - d)Every atom of the same element has the same # of p +

3. Atomic Number is the # of p + ElementAtomic ## of Protons Carbon Phosphorus Gold

4. Mass Number is the # of p + + n 0 C 12 6 Mass Number Atomic Number Element Symbol

5. 5. Isotope of an element- same # p +, different # of n 0 (Same atomic #, different mass #) 6. Atomic mass unit (amu)- defined as 1/12 of the mass of a Carbon-12 atom

7. Atomic Mass- mass averaged of all the isotopes of an element. Parentheses Indicate Mass of Most Stable Isotope Back to Main Page

8. Isotopic Name: Carbon-12 or Carbon-14 a. b. Hydrogen-3 c. Magnesium-27 Mass Number Ne Mg p + e- n 0 10 p + e- n

Isotope Lab Avg. mass = Mass (of that type of veggie) # of pieces of that type of veggie % abundance = # of pieces of that veggie × 100 Total # of pieces of all veggies

Bell Work 9/21 The nucleus consist of ______ and _______. The ______ number of an atom gives the number of protons. The _____ number gives you how many protons and neutrons are in the nucleus. Na _________ _________ Atoms that have the same _______ ________ but different numbers of neutrons are ________ of the same element. Since isotopes have different numbers of neutrons, they have a different _______ ______. Copper-63 _________

C. Nuclear Symbols Chlorine-37 Chlorine-37 –atomic #: –mass #: –# of protons: –# of electrons: –# of neutrons:

Mg Nuclear Symbol Examples Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons Cl Atomic Number Mass Number Number of Protons Number of Neutrons Number of Electrons

Average Atomic Mass Average Atomic Mass weighted average of all naturally occuring isotopes weighted average of all naturally occuring isotopes on the Periodic Table on the Periodic Table round to 2 decimal places round to 2 decimal places Avg. Atomic Mass

Avg. Atomic Mass Average Atomic Mass Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O. EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O amu

Avg. Atomic Mass Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O. EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O amu

Avg. Atomic Mass E. Average Atomic Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine amu

Example: A sample of cesium is 75% 133 Cs, 20% 132 Cs and 5% 134 Cs. What is the average atomic mass? Answer:.75 x 133 = x 132 = x 134 = = average atomic mass