Atomic Structure: Images of the Invisible

1. Atomic Structure: Images of the Invisible

2. Overview • Parts of the Atom. • The Property Charge • Electrolysis: Positive and Negative • Ions • Discovery of the electron • Discovery of the nucleus • Radioactivity • Elements: Mass and Atomic Number • Isotopes • Electron Arrangement: The Bohr Model

3. Subatomic Particles In an atom: #p+ = #e- Net charge = 0

4. Subatomic Particles of the Atom • An atom consists • of a nucleusthat contains protonsand neutrons. • of electronsin a large, empty space around the nucleus.

5. E Electrolysis Electrolyte: A compound that conducts electricity when molten or dissolved in water. Electrodes: Carbon rods of metallic strips that carry electrical current. • Anode: A positiveelectrode. • Cathode: A negativeelectrode.

6. Ions Ion: An atom or group of atoms with a charge. Anion: A negative ion. more e- than p+ Cation: A positive ion. more p+than e-

7. Cathode Ray Tubes Mid-1800s: Crookes’ tube J.J. Thomson found that Cathode Rays could be deflected by an electric field (because they had a charge) . This was the discovery of the ELECTRON By comparing the deflection of a beam of cathode rays by electric and magnetic fields he was able to measure the particle's mass.

8. Electron Charge 1909, Robert Millikan: Using the oil-drop experiment, Millikan discovered the charge of an electron. 1

9. Rutherford Gold Foil Experiment Using an apparatus similar to that shown below, Ernest Rutherford discovered the atomic nucleus. Positively charged particles were aimed at atoms of gold. Mostly went straight through the atoms were deflected only occasionally. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close

10. X-Rays 1895, Wilhem Roentgen: Using a cathode ray tube, Roentgen discovered X-rays.

11. Radioactivity 1895, Antoine Becquerel: Discovered radioactivity. Marie Curie and husband Pierre characterized radioactivity.

12. Three Types of Radioactivity

13. Three Types of Radioactivity 1

14. Subatomic Particles 1

15. Elements • Elementsare • pure substances that cannot be separated into simpler substances by ordinary laboratory processes. • the building blocks of matter. • Each element is made up of one kind of atom • defined by the number of protons in the nucleus of the atom • gold (79 p+) carbon (6 p+) aluminum (13 p+)

16. Electron Configurations and the Periodic Table

17. Elements Identify each statement as describing a 1) proton, 2) neutron, or 3) electron. A. found outside the nucleus B. has a positive charge C. is neutral D. found in the nucleus

18. Atomic Structure: Z and A Atomic number: The number of protons in a nucleus. Mass number: The sum of protonsand neutrons in a nucleus. Z X A X = Element symbol Z = Atomic number (#p+) A = Mass number ( #p+ + #n)

19. Isotopes Isotopeshave the same atomic number, but have different mass numbers (same number of protons, but different number of neutrons). Nucleus has 1 proton and no neutrons Mass # =1 Nucleus has 1 proton and 1 neutrons Mass # =2 Nucleus has 1 proton and 2 neutrons Mass # =3

20. Worked Example 3.1 92 How many neutrons are there in the nucleus? U 235 235 U Solution 92 Simply subtract the atomic number Z(number of protons) from the mass number A(number of protons plus neutrons). There are 143 neutronsin the nucleus. 40 Exercise 3.1B K 19 A potassium isotope has 21 neutronsin its nucleus. What is the mass number ? A = Mass number = #p+ + #n 19 + 21

21. Atomic Structure Isotopes are elements that differ only in their: a. Atomic number b. Nuclear charge c. Number of electrons in the neutral atom d. Atomic mass e. Chemical properties d. Atomic mass

22. Electron Arrangement:The Bohr Model Flame tests: Different elements give different colors to a flame. Li Na K Ca Sr Alkali metals

23. Continuous spectra: When light emitted from a solid substance is passed through a prism, it produces a continuous spectrum of colors. Electron Arrangement:The Bohr Model

24. Line spectra: When light from a gaseous substance is passed through a prism, it produces a line spectrum. Electron Arrangement:The Bohr Model

25. Electron Arrangement:The Bohr Model Quantum: A tiny unit of energyproducedor absorbedwhen an electronmakes a transition from one energy level to another.

26. Electron Arrangement:The Bohr Model When electrons are in the lowest energy state, they are said to be in the ground state. When a flame or other source of energy is absorbed by the electrons, they are promoted to a higher energy state (excited state) . When an electron in an excited state returns to a lower energy state (), it emits a photon of energy, which may be observed as light.

27. Electron Arrangement Energy states or levels are sometimes called shells.

28. Summary • Atomare composed of electrons (e-), protons (p+), and neutrons (n): • p+and n are in the nucleus; e- ‘orbit’ the nucleus • Opposite charges attract; same charge repels • The J.J. Thomson’s use of Cathode Rays and Millikan’s oil-drop experiment describe the e- • Rutherford’s gold foil experiment led to the nucleus • Radioactivity: a (+), B (-), g • Elements: Mass and Atomic Number • Isotopes: sameAtomic Number. Different # n • Electron Arrangement: The Bohr Model • Energy states or levels for e- are sometimes called shells