1. Ch. 4 - Atomic Structure 1

2. Democritus’s Atomic Philosophy
Greek philosopher, first to propose idea of atoms
a tomos – “un cuttable”
Failed theory:
Lacked experimental support
Couldn’t explain chemical behavior
Democritus (400 BC) 2

3. Defining the Atom
Atom
The smallest particle of an element that retains the chemical identity of that element (pg. 101) 3

4. Law of Conservation of Matter (Antoine Lavoisier)
Law of Constant Composition (Joseph Proust)
Elements combine in whole-number ratios to form compounds.
e.g., water (H2O) is always 2 hydrogen to 1 oxygen
Btw, by early 1800’s, there was no connection between elements and atoms; all atoms were assumed to be identical. 4

5. Dalton’s Atomic Theory
Jons Jakob Berzelius ( ) Swedish chemist who invented modern chemical symbols.
Berzelius discovered the elements silicon, selenium, cerium, and thorium.
John Dalton
1803 5

6. Dalton’s Atomic Theory
1. All matter (elements) is composed of tiny indivisible particles called atoms.
2. Atoms of the same element are identical – but different from those of another element.
3. Atoms of different elements can physically mix, or combine in whole-number ratios to form compounds
4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. 6

7. Dalton’s Atomic Theory
Atoms of Element A
Atoms of Element B
PHYSICALLY mixed
CHEMICALLY combined
Fig. 4.2, pg. 102 7

8. Avg. atomic radius = 5×10-11 m – 2×10-10 m
Sizing Up the Atom
Scanning Tunneling Microscope (STM)
“Nanotechnology”
Instrument used to “see” atoms
Avg. atomic radius = 5×10-11 m – 2×10-10 m 8

9. Kanji characters for atom, “original child.”
4.1 Homework
#1, 2, 4 – 7
4.2 Homework
#8, 9

10. Ch. 4 Atomic Structure
4.2 The Nuclear Atom
pgs 10

11. Subatomic Particles Atoms are divisible. 3 subatomic particles
Proton, p+
Electron, e-
Neutron, no 11

12. Subatomic Particles J.J. Thomson
“Found” the electron, a negatively charged particle with very small mass.
Cathode-ray tube, 1897 12

13. Deflected Cathode-ray
Movie!! 13

14. Thomson’s “Plum-Pudding” Model14

15. The Atomic Nucleus Ernest Rutherford
“Discovered” atomic nucleus, tiny central core of an atom
Gold-foil experiment, 1911 15

16. Rutherford’s Gold-foil exp.
Movie!! 16

17. 17

18. The Nuclear Atom 18

19. The nucleus of the atom is much smaller than the atom yet contains most of its mass.19

20. Ch. 4 Atomic Structure
4.3 Distinguishing Among Atoms
pgs 20

21. Periodic Table Intro 21

22. Family
Periodic Table Intro
Period 22

23. Periodic Table Intro Alkali Metals Family
Family (or group) – vertical column; elements within a family share similar chemical properties.
Period – horizontal row;
Alkali Metals Family 23

24. Atomic Number the number of protons in the nucleus of an atom.
Each element has a unique number of protons.
For neutral atom, the number of protons equals the number of electrons. 24

25. Mass Number the total number of protons plus neutrons.
For neutral atom, the number of protons equals the number of electrons.
e- mass not included; negligible. 25

26. Chemical Symbols (pg. 161)
LARGER #
smaller # 26

27. Ion – lose electron(s) a charged atom or group of atoms.
formed when atoms gain or lose electrons.
Cation – positive ion; p+ > e-
– lose electron(s)
Anion – negative ion; p+ < e-
– gain electron(s)
CA ION 27

28. Isotopes
atoms that have the same atomic number but different mass numbers;
same number of protons, but different number of neutrons. 28

29. Atomic Mass
a weighted average mass of all naturally occurring isotopes;
determined from mass and relative abundance for each isotope.
Average Atomic Mass =
(massisotope 1 × rel. abundanceisotope 1) +
(massisotope 2 × rel. abundanceisotope 2) + … 29