Atomic Structure

1. Atomic Structure

2. Early discoveries of the atom Democritus: Supported the �continuous� view of matter. States that there is a point where matter cannot be further divided He called the smallest particles possible �atomos� meaning indivisible

3. Other discoveries Joseph Priestley: Prepared oxygen from a compound of mercury and oxygen Antoine Lavoisier: Performed experiments which lead to the law of conservation of mass Joseph Proust: Performed experiments leading the law of definite proportions

4. Law of definite proportions A compound always contain elements in certain definite proportions and in no other combinations

5. Dalton�s atomic theory Developed by John Dalton Theory was based on experiments from Lavoisier & Proust

6. Dalton�s atomic theory All elements are made up of tiny indivisible particles called atoms All atoms of a given element are identical and have the same properties

7. Dalton�s atomic theory (cont.) Atoms of different elements combine to form compounds Compounds contain atoms in small whole number ratios Atoms can combine in more than one ratio to form compounds

8. Dalton�s theory is based on experimental results. Democritus views was based on philosophy Dalton�s theory states that atoms were �indivisible�. Atoms are not indivisible

9. The discovery of the electron Thomson determined the mass-charge ratio of the electron Thomson formulated the �plum pudding� model of the atom

10. Robert Millikan Performed the �oil drop� experiment Based on his results, was able to determine the charge of the electron From the mass-charge ratio and the charge, one can determine the mass of the electron

11. Ernest Rutherford Discovered radioactivity (alpha, beta, and gamma radiation) Developed the �gold foil experiment�

12. Observations of gold foil experiment Most alpha particles went through the gold foil Some alpha particles were deflected as they went through foil A smaller number bounced backward

13. Conclusions The atom is mostly empty space The nucleus occupies a very small region of the atom and it is positively charged The nucleus contains nearly all the mass of the atom

14. Atomic notation Every element has a characteristic number of protons associated with it Atomic number is the number of protons Mass number is the number of protons and neutrons

15. Isotopes Isotopes are atoms with the same number of protons, but different number of neutrons

16. Atomic Mass unit 1/12 the mass of a carbon-12 isotope. Mass of carbon-12 is 12.000 amu

17. Atomic mass This the weighed average of all naturally occurring isotopes in an element

18. Electromagnetic spectrum Consists of all the known radiations Range from gamma radiation to radio waves

19. Electromagnetic radiation (cont.) Has two characteristics: a) wavelength and b) frequency

20. Wavelength & frequency Wavelength: Distance between peaks of two waves. Symbol is l (lambda) Frequency: number of waves that passes through a given point in a second. Symbol is n (nu)

21. Wavelength & frequency (cont.) Wavelength & frequency are inversely related to each other. The product of wavelength and frequency gives the velocity of light c = ln, c is the velocity of light c = 3.00 x 108 m/s

22. Visible light Wavelength range: 400-750 nm Consists of seven primary colors (ROYGBIV) Visible light constitutes only a small region of the electromagnetic spectrum

23. Other forms of radiation ultraviolet: Sometimes called black light Three categories: uv-a, uv-b and uv-c Uv-c is the strongest in frequency, uv-a is the weakest in frequency

24. Other forms of radiation (cont.) Infrared: Normally radiant heat energy Infrared rays are too long to observed by the human eye Microwaves: Causes molecules to rotate Microwaves tend to �bounce off� an object and return to the source

25. Electrons & spectra Line spectrum: pattern of colored lines emitted (given off) by each element

26. Quantum theory Formulated by Max Planck and Albert Einstein Proposed that light is emitted in discrete packets of energy, called photons

27. Quantum theory (cont.) Energy increases directly with the frequency of light based on the equation: E = hn h is Planck�s constant h= 6.63 x 10-34 J s

28. Niels Bohr Formulated the �planetary model� of the atom

29. Electrons in Atoms Niels Bohr: Suggested that electrons of atoms exist in specific energy levels When an electron absorb photons, the electron is elevated to a higher energy level (excited state) The electron then falls to a lower energy level, and energy is given off (emitted)

30. Contribution of Bohr model of the atom Bohr was able to deduce that each energy level holds a certain number of electrons: 1st energy level - Holds a max. of two electrons 2nd energy level � Holds a max. of eight electrons 3rd energy level � Holds a max. of 18 electrons

31. Bohr�s model (cont) Maximum number of electrons held = 2n2 n is the energy level number

32. Drawbacks of the Bohr model Model works best only for hydrogen and hydrogen-like atoms Not successful in predicting spectra of more complex atoms

33. Energy levels and sublevels Energy level that results from splitting a main energy level Carries the designations: s, p, d, and f

34. The maximum number of electrons depends on the type of energy sublevel

35. Electron configurations This is a shorthand statement describing the location of electrons by sublevel

36. Quantum mechanical model of the atom Erwin Schrodinger: formulated wave equations Equations correspond to the regions of high probability, called orbitals

37. Quantum mechanical model of the atom (cont.) Werner Heisenberg: Developed the uncertainty principle

38. Heisenberg uncertainty principle It is impossible to predict the position and energy of an electron simultaneously

39. Our model of the atom is not yet complete