2. Basic Atomic Structure Democritus Dalton Subatomic Particles Symbol Notation Isotopes Average Atomic Mass

3. Democritus (460-370BC)  Before Democritus… Classification system: earth, wind, fire, water  Named parts of matter “atomos.”  (translation: not able to be cut)  How did he come up with this?  Later scientists realized that the atom consists of charged particles.

4. John Dalton’s Atomic Theory of Matter  All elements are composed of tiny indivisible particles called atoms  Atoms of the same element are identical, atoms of different elements are different and have different properties.  Atoms of different elements can mix in whole number ratios to form compounds  Chemical reactions cause atoms to separate, but not change into different atoms  Which hold true?

5.  Law of Constant Composition (Proust): In a given compound the relative numbers and kinds of atoms are constant. (postulate #3)  Law of Conservation: matter can neither be created nor destroyed (postulate #4)  NEW** Law of Multiple Proportions: If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole #’s. Water Vs. Hydrogen Peroxide 8.0g of O combines with 1.0g of H to form water 16g of O combines with 1.0g of H to form hydrogen peroxide What can you conclude about the ratios of hydrogen and oxygen in these two compounds?

6. Subatomic Particles

7. Three Kinds of Sub-Atomic Particles Protons: +1.602x10 -19 C charge Neutrons: NO charge Electrons: -1.602x10 -19 C charge Atoms have an equal # of protons and electrons so they have no NET electrical charge. For convenience, the charges are expressed as multiples rather than in coulombs. Protons have a +1 charge while electrons have a -1 charge.

8. Comparing Subatomic Particles The proton gives identity to an atom, the electron gives personality.

11. Ernest Rutherford: http://www.learnerstv.com/animation/ani mation.php?ani=121&cat=Chemistry Conclusion: the nucleus is small and highy positive. Most of the atom is empty space.

12. Mass Number & Atomic Number Mass Number = Number of protons + neutrons Atomic Number = Number of protons

13. Complete the Table SymbolAtomic Number Mass Number Number of p + Number of n 0 Number of e - 9 10 Na 15 47 25 55 25 S 2- 32 Ga 3+ 39

14. Isotopes Have the Same…  Number of protons  Atomic Number  Number of electrons

15. Isotopes Have Different…  Number of neutrons  Mass Number  Mass n0n0

17. Isotopes of Hydrogen Hydrogen-1 Hydrogen-2 Hydrogen-3 ProtiumDeuteriumTritium

18. The mass of an atom is EXTREMELY small! The heaviest known atom is 4x10 -22 g. For convenience, (thank you)... we express the size of atoms in a derived unit, the a.m.u. (Atomic Mass Unit) Diameters of atoms fall between 1x10 -10 m and 5x10 - 10 m, or 100-500pm, or 1-5Angstroms 1A=10 -10 m (both pm and A are commonly used) How many atoms are in one penny? 24,000,000,000,000,000,000,000 or 2.4 x 10 22 How many people live on this planet? 6,000,000,000 or 6 x 10 9

20. Atomic Mass Unit (amu)  carbon-12 isotope used as standard  1 atom of carbon-12 = 12 amu  carbon-12 has 12 particles with mass  mass of proton = 1 amu  mass of neutron = 1 amu 12 C 6

21. Average Atomic Mass  Weighted average of all isotopes  Seen as mass number on periodic table  Units in amu

22. To Calculate Average Atomic Mass You Need… Number of Isotopes Mass of Isotopes Percent Relative Abundance

23. Calculating Average Atomic Mass Mass x Rel. Abundance Average Atomic Mass Isotope A Isotope B

24.  AVERAGE ATOMIC MASS  CALCULATING AVERAGE ATOMIC MASS Atomic Mass or Atomic Weight: a calculated percentage of existing isotopes according to abundance: mass isotope x % abundance (DECIMAL FORM) mass isotope x % abundance + mass isotope x % abundance

25.  Find the Number of Neutrons: a) Oxygen-17 d)Bromine- 80 b) 32 S e) 207 Pb c) 108 Ag f) 25 Mg 47 12  Write the symbols for each element with the correct atomic number and mass number in proper notation a) O-16, O-17, O-18 b) Cr-50, Cr-52, Cr-53

26.  Element X has two natural isotopes... X-10 and X-11 X-10 weighs 10.012amu and is 19.91% abundant X-11 weighs 11.009amu and is 80.09% abundant What is the atomic mass?  Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of 34.969amu, and 24.22% 37Cl, which has an atomic mass of 36.966amu. Calculate the average atomic mass of chlorine.

27.  Three isotopes of silicon occur in nature: 28Si (92.23%), which has a mass of 27.97693amu; 29Si(4.68%), which has a mass of 28.97649amu; and 30Si(3.09%), which has a mass of 29.97377amu. Calculate the atomic weight of silicon.  Boron has two isotopes, B-10 and B-11... Which is more abundant?  Silicon has 3 isotopes, Si-28,29,30 Which is more abundant?