Atomic Structure What is an atom? The smallest particle of an element that retains properties of that element. Gedanken 1
Atomic Theory Democritus vs. Dalton 500 BC 1808 AD Pure thought Observation + experiment Matter is like Legos. It is not continuous! Weird. 2
Dalton s Atomic Theory Elements composed of atoms Atoms of element are identical* Compounds: simple ratios of atoms (H 2 O) Chem reaction: rearrangement, not creation, of atoms 3
Atomic Size A penny has 2.4 x 10 22 Cu atoms = 24 000 000 000 000 000 000 000. Vs. Earth s population of 6 x 10 9 = 6 000 000 000. 4
Subatomic Particles Atom comprised of 3 particles: electron e - proton p+ neutron n 5
6 Electron J. J. Thomson: 1897
Proton E. Goldstein: 1886 Atoms are neutral, so there must be a + particle: proton (p+). p + is 1840x more massive than e - 7 e - p +
Neutron J. Chadwick: 1932 Neutron: neutral particle nearly same mass as proton. Why did it take so long to discover the neutron? 8
Mass Units Mass p + = 1.673 x 10-24 g Mass n = 1.675 x 10-24 g ~1.0 amu Definition: atomic mass unit 1 amu = 1/12 th mass of carbon atom that contains 6 p + & 6 n 9
Subatomic Particles Charge (g) Mass (amu) p + +1 1.673 x 10-24 1 10 n 0 1.675 x 10-24 1 e - -1 9.11 x 10-28 1 1840
11 Atomic Structure E. Rutherford: 1911
12 E. Rutherford: 1911 Expected Actual
E. Rutherford: 1911 Conclusions: Most of atom is empty space Mass concentrated in nucleus Nucleus is positively charged 13
Nucleus: Small & Massive e - e - p + n 14 e -
Nucleus: Small & Massive Analogy 15
Gedanken What keeps you from falling through a wall? 16 Electrons (on outside of atom) determine chemical properties.
Atoms of Different Elements If all atoms have the same subatomic particles, what makes a carbon atom different from an oxygen atom? 17
Atomic Number: Z Z = number of protons Z determines element Periodic Table is arranged by Z 18
19 Periodic Table
Mass Number Mass number = # p + + # n (in nucleus) Recall: nearly all mass of an atom is in the p + and n. 20
Atomic Symbols mass number (#p + + #n) atomic number (#p + ) # p + = 7 # n = 14 7 = 7 # e - = 7 (atom is neutral) 14 7 N 21
Atomic Symbols Shorthand: 14 7 N = Nitrogen-14 4 2 He = He-4 22
Atoms: First 4 Elements Symbol At. # Mass# p + e - n H 1 1 1 1 0 He 2 4 2 2 2 Li 3 7 3 3 4 Be 4 9 4 4 5 23
Atoms: You try! 24 Symbol At. # Mass # p + e - n 7 7 9 10 39 19 59 27 C 8
Isotopes Atoms with same number of p + (the same element) but different number of n. 12 14 6 C and 6 C 6 n 8 n 25
Isotopes Neon-20 Neon-21 Neon-22 10 p + 10 p + 10 p + 10 n 11 n 12 n 10 e - 10 e - 10 e - What are the same and different 26 for isotopes of an element?
Atomic Mass Why aren t masses on the Periodic Chart whole numbers? e.g. Chlorine mass listed as 35.453 amu 27
Atomic Mass Periodic Table lists weighted average mass of naturally existing isotopes. e.g. Cl-35 abundance 75.8 % Cl-37 abundance 24.2 % 28
Calculating Atomic Mass Cl-35: 29 For each isotope take the fractional abundance times mass. Then add. Cl-37: 75.8% x 35.0 amu = 26.5 amu 100% 24.2% 100% x 37.0 amu = 9.0 amu total = 35.5 amu
Atomic Mass: Try It Calculate the atomic mass of silicon give the following data: Isotope Abundance Mass(amu) Si-28 92.2% 27.98 Si-29 4.7% 28.97 Si-30 3.1% 29.97 30
Periodic Table http://www.wimp.com/thegenius/ Mendeleev: mid-1800s arranged known elements by properties and mass. now arranged by Z 31 (Moseley, 1913)
Periodic Table Rows Periods period numbers: 1, 2, 3 etc Columns Groups or Families group numbers: 1, 2, 3, etc. 32
Periodic Table Metals & Nonmetals Metals high luster high electrical conductivity ductile malleable 33
Periodic Table Nonmetals nonlustrous poor conductors of electricity brittle 34
Periodic Table Metalloids B, Si, Ge, As, Sb, & Te computer chips 35
Periodic Table Representative Elements Transition Elements Inner Transition Elements 36
Periodic Table: Groups Group 1. Alkali Metals Group 2. Alkaline Earth Metals Group 17. Halogens Group 18. Noble or Inert Gases 37
Diatomic Elements Hydrogen H 2 Fluorine F 2 Oxygen O 2 Nitrogen N 2 Chlorine Cl 2 Have No Fat Bromine Br 2 38 Iodine I 2
States of the Elements At STP: which elements are liquids? which elements are gases? which elements are solids? 39
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Warm-up Name the subatomic particles that make up the atom. Where is each particle located within the atom? 41
Warm-up What were the four points of Dalton s atomic theory? Fill in the chart: Particle Mass Discoverer Location Which particle is the most important in chemistry? 42
Warm-up: Define atomic no. & mass no. Fill in the chart. Symbol At. Mass p + e - n No. No. 8 8 16 17 48 22 43 Al 15
Warm-up Define atomic mass and mass number. Lithium has two isotopes, Li-6 with a mass of 6.02 amu that is 7.42% abundant and Li-7 with a mass of 7.02 amu that is 92.58% abundant. Calculate the atomic mass of lithium. 44