1. Chapter 4 Atomic Structure

2. Defining the Atom  All elements are composed of particles called atoms  All atoms of the same element are identical  Atoms of different elements combine to form compounds  Atoms of one element can never be changed into another element

3. History of the Atom   Democritus (Greek 460-370 BC) 1 st to use the word atom Believed that atoms were indivisible & indestructible No scientific support  Aristotle (Greek 384-322 BC) Rejected the theory of atoms Believed in 4 core elements fire, air, water, earth

4.  Antoine Lavoisier (French 1743-1794) Law of Conservation of Matter –Law of Conservation of Matter – Matter is not created or destroyed during a chemical reaction

5.  Joseph Proust (French 1754-1826) Law of Definite Proportions -Law of Definite Proportions - A compound is always composed of the same elements, in the same proportion by mass

6.  John Dalton (English 1766-1844) Studied the ratio in which elements combineStudied the ratio in which elements combine Quantitative data – massQuantitative data – mass -Law of Multiple Proportions - When 2 elements form more than one compound, they do so in a ratio of whole numbers When 2 elements form more than one compound, they do so in a ratio of whole numbers

7. Dalton’s Atomic Theory 1.All elements are composed of indivisible ‘solid sphere’ atoms. 2.All atoms of a given element are identical. 3.Atoms of different elements differ in their masses. 4.Different atoms combine in simple whole number ratios to form compounds.

8. Structure of the Atom

9. Subatomic Particles  Today… Dalton’s Atomic Theory has one important change  Atoms are divisible…  3 types of subatomic particles ProtonsProtons NeutronsNeutrons ElectronsElectrons

10. Electrons  J.J. Thomson (English 1897) – Identified the 1 st subatomic particleIdentified the 1 st subatomic particle Cathode-ray tubeCathode-ray tube

12. Thomson’s Electron Model  Named electrons  Symbol: e -  Charge: (-1)  Mass: ~ 0 amu  Plum Pudding/ Chocolate Chip Cookie

13. What about the protons & neutrons?  Protons Symbol: p +Symbol: p + Charge: (+1)Charge: (+1) Mass: 1 amuMass: 1 amu  Neutons Symbol: n 0 Charge: (0) neutral Mass: 1 amu

14. The Nucleus  Ernest Rutherford (English 1911) - Discovered the ‘structure’ of the atomDiscovered the ‘structure’ of the atom Gold foil experimentGold foil experiment Rutherford’s Gold Foil Experiment

15. Rutherford’s Nuclear Model  Atom is mostly empty space  Atoms have a dense center – nucleus  Most of the mass is in the nucleus  Nucleus has a positive charge  Protons & neutrons are located in the nucleus  Electrons are outside of the nucleus & occupy most of the atom’s volume

16. Distinguishing Among Atoms

17. What makes atoms different from one another?  # of protons  Atomic number = # of protons  Usually written as a subscript Mg 12 or 12 Mg What element has 11 protons? How many protons does potassium have? Sodium 19

18. How do you determine the # of neutrons?  Atomic mass = # protons + # neutrons  Usually written as a superscript 12 C or C 12 or C -12  # of neutrons is the difference between the atomic mass & the atomic number # of neutrons = atomic mass - atomic #

19. What is the atomic mass of helium? What element has an atomic mass of 27? How many protons does this element contain? How many neutrons does this element contain? 4.0026… round to 4 Aluminum 13 27 – 13 = 14

20. What about electrons?  # electrons = # of protons  Why? Atoms are electrically neutralAtoms are electrically neutral How many electrons does sulfur contain? Which element contains 10 electrons? 16 Neon

21. Sample Problems  How many protons, neutrons and electrons are in each atom? Beryllium (Be) - Fluorine (F) - Hydrogen (H) - 4, 5, 4 9, 10, 9 1, 0, 1

22.  How many neutrons are in each atom? 8 O 16 47 Ag 108 82 Pb 207 16 – 8 = 8 108 – 47 = 61 207 – 82 = 125

23.  Express the composition of each atom in shorthand form. Nitrogen -14 Sodium - 23 Phosphorus -31 p + = 7, n 0 = 7, e - = 7 p + = 11, n 0 = 12, e - = 11 p + = 15, n 0 = 16, e - = 15

24. Isotopes  Atoms that contain the same number of protons but have different numbers of neutrons  Different atomic masses  Does not change the atom’s identity  Are naturally occurring  Symbols: 11 Na 23 or 11 Na 24 6 C 12 or 6 C 13 or 6 C 14

25.  Determine the number of protons, neutrons and electrons in the following: 1 H 1 1 H 2 1 H 3 p + = 1, n 0 = 0, e - = 1 p + = 1, n 0 = 1, e - = 1 p + = 1, n 0 = 2, e - = 1

26. Determining the Atomic Mass  Atomic mass # is an average of atom’s naturally occurring isotopes Copper has 2 isotopes Cu-63 and Cu-65 Which isotope is most abundant? There are 3 isotopes of Silicon with mass numbers of 28, 29, and 30. Which is more abundant? 63 Si -28

27. Calculating the Atomic Mass  Multiply the mass of each isotope by its natural abundance (expressed as a decimal), then add the products  Practice…

28. Ions  An atom with an electrical charge  Occurs 2 ways: Oxidation – loss of an e -Oxidation – loss of an e - results in a (+) charge results in a (+) charge Reduction – gain of an e -Reduction – gain of an e - results in a (-) charge results in a (-) charge Mnemonic: ‘Leo says Ger’ Loss of electrons = oxidation Gain of electrons = reduction

29. Examples of Ions H+H+H+H+  Cl -  As 3-  Mg 2+  Oxidation State – Number found on the periodic tableNumber found on the periodic table Shows the number of e - gained or lostShows the number of e - gained or lost Many elements have more than one numberMany elements have more than one number Lost 1e - Gained 1e - Gained 3e - Lost 2e -