Early Models of the Atom

1. Early Models of the Atom History of the Atom Standard Atomic Notation Some Intro Songs for your entertainment: The Atom Song: http://www.youtube.com/watch?v=vUzTQWn-wfE&NR=1 (3 min) A Rap: http://www.youtube.com/watch?v=5E2cIovfpO0&NR=1 (2 min)

2. HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC • - ancient Greek philosopher • suggested that matter was made up of tiny particles called: • his theory was not accepted for 2000 years ATOMOS (greek for indivisible)

3. HISTORY OF THE ATOM John Dalton 1808 - working with gases, reconsidered Democritus’ theory that particles are indivisible - suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them: ATOMS

4. History of the Atom Dalton’s Atomic Model: • All matter is made up of atoms, which are particles too small to see • Each element has its own kind of atom, with its own particular mass • Compounds are created when atoms of different elements link to form molecules • Atoms cannot be created, destroyed, or subdivided in chemical changes

5. Problem with Dalton’s Theory: – unable to explain the Electrical nature of matter: Like charges repel Unlike charges attract

6. History of the Atom 1879William Crookes • worked with cathode ray tubes • beam of particles was attracted to a positive plate • these particles were called: ELECTRONS - have a negative charge

7. History of the Atom 1886Eugen Goldstein • most samples of matter are NOT charged • the atom must contain positively charged particles • used cathode ray tubes to prove this and they were called: • PROTONS

8. HISTORY OF THE ATOM Joseph John Thompson 1898 - atom had a positive core and electrons were embedded in this

9. HISTORY OF THE ATOM 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING MODEL Or RAISIN BUN MODEL

10. HISTORY OF THE ATOM Ernest Rutherford 1910 • designed an experiment using RADIUM (this element spits out positive ALPHA particles) • - he placed a piece of gold foil in front of the beam, surrounded by a screen to detect the path of the particles • - they found that although most of them passed through, about 1 in 10,000 hit

11. HISTORY OF THE ATOM gold foil helium nuclei helium nuclei They found that while most of the particles passed through the foil, a small number were deflected and, to their surprise, some particles bounced straight back.

12. Rutherford’s Gold Foil Experiment Rutherford & Bohr (4 min) http://videos.howstuffworks.com/hsw/25133-icons-of-science-bohr-and-the-structure-of-the-atom-video.htm

13. HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in the central nucleus. This held the electrons in place by electrical attraction However, this was not the end of the story.

14. History of the Atom 1932Chadwick • Nucleus contains another particle which has NO charge (neutral) called a: NEUTRON - This particle and the proton have approximately the same mass, but the electron is very small. It takes 1837 electrons to have the same mass as ONE proton or neutron.

15. HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

16. Bohr’s Atom electrons in orbits nucleus

17. The Structure of Atoms (2 min) • http://videos.howstuffworks.com/hsw/18057-elements-of-chemistry-the-structure-of-atoms-video.htm

18. HELIUM ATOM Shell proton N + - + N - neutron electron What do these particles consist of?

19. ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

20. STANDARD ATOMIC NOTATION 4 He Mass number the number of protons and neutrons in an atom Atomic number 2 the number of protons in an atom Atomic number = number of electrons = number of protons mass number – atomic number = number of neutrons

21. ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • first shell a maximum of 2 electrons • second shell a maximum of 8 electrons • third shell a maximum of 8 electrons

22. ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams

23. ELECTRONIC CONFIGURATION With electronic configuration, elements are represented numerically by the number of electrons in their shells and number of shells. For example; Nitrogen configuration = 2 , 5 14 2 in 1st shell 5 in 2nd shell N 2+5 = 7 7

24. ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; 23 16 40 Na O Ca a) b) c) 11 20 8 2,8,8,2 2,8,1 2,6 28 11 35 Cl Si B d) e) f) 17 14 5 2,8,7 2,8,4 2,3

25. DOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X 14 Nitrogen N X X N X X X X

26. DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; X 16 35 X O Cl a) b) X X 8 17 X X X X X Cl X X X X X X X O X X X X X X X X X X NOTE ABOVE: Atomic number = # of protons = # electrons (in neutral atom) If time, check out the first 20 elements: http://www.sciencesource2.ca/resources/flt_atom_builder.swf

27. SUMMARY • The Atomic Number of an atom = number of • protons in the nucleus. • The Atomic Mass of an atom = number of • Protons + Neutrons in the nucleus. • The number of Protons = Number of Electrons. • Electrons orbit the nucleus in shells. • Each shell can only carry a set number of electrons.

28. This powerpoint was kindly donated to www.worldofteaching.com http://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching. S.Morris 2006 – outline of this powerpoint