Atomic Theory

1. Atomic Theory

2. In the Beginning • Atoms originally named by Democritus • Believed the a substance could be divided over and over again only to a point • If divided further it would not be that substance anymore • His atoms were solid, _________________________

3. Lavoisier: Law of Conservation of Mass • Precisely measured masses of reactants and products of chemical rxns • Law of conservation of __________- mass is neither created or destroyed in chemical rxn • Mass of reactants equals the mass of the products

4. Proust: Law of Definite Proportions • All samples of a particular compound have the same _______________ • Elements have the same proportion by mass in each sample

5. DALTON: LAW OF MULTIPLE PROPORTIONS • If two or more compounds containing the same two elements are examined (for example: CO and CO2) • Then the ratio of masses of the element that changes in both compounds (in our example: O) is a small whole number

6. Law of Multiple Proportions (cont.) Four different oxides of nitrogen can be formed by combining 28 g of nitrogen with: 16 g oxygen, forming Compound I 48 g oxygen, forming Compound II 64 g oxygen, forming Compound III 80 g oxygen, forming Compound IV Compounds I–IV are N2O, N2O3, N2O4, N2O5 What is the ratio 16:48:64:80 expressed as small whole numbers?

7. John Dalton • Proposed atomic theory in 1803 • Four ideas • All matter is composed of indivisible particles called atoms. • All atoms of one element are alike in mass and other properties, but the atoms of one element are different that the atoms of other elements. • Compounds are formed when atoms of elements unite in fixed proportions. • No atoms are created, destroyed, or broken apart in chemical reactions. Atoms are just rearranged • His atom is also a solid, _____________________

8. Dalton’s Theory Satisfies Laws … six fluorine atoms and four hydrogen atoms after reaction. Mass is conserved. Six fluorine atoms and four hydrogen atoms before reaction … HF always has one H atom and one F atom; always has the same proportions (1:19) by mass.

9. J.J. Thomson and Cathode Rays • Worked with cathode ray tubes (made by Sir William Crooke) in the late 1800’s • Found that all matter had negative particles (___________________) • Calculates _______________ ratio of e-

10. J.J. Thomson’s Model • Atoms have negative particles, but overall they are neutral • His atom has a positive sphere with negative particles embedded (often called the _______________________)

11. Robert Millikan’s Oil Drop Experiment Calculated the charge of an e- Made it possible to calculate the mass of the e- Charged droplet can move either up or down, depending on the charge on the plates. Radiation ionizes a droplet of oil. Magnitude of charge on the plates lets us calculate the charge on the droplet.

12. Rutherford’s Experiment • Often called the ____________ experiment • Expected almost all  particles to pass straight through the gold • Although many did, some particles were reflected back

13. Rutherford’s Conclusion • Atom must have positive particles (_______________) concentrated in the center • Center is called the ______________ • Electrons gravitate around the nucleus • A lot of _________________ between nucleus and electrons

14. James Chadwick • Discovered neutrally charged particles (_________________) • Particle was also found in the ______________

15. Niels Bohr • Refined Rutherford’s atom model • Put the electrons in fixed _______ (like planets orbiting around the sun) • Electrons could temporarily get excited and jump levels

16. Modern Atomic Model • Electron behave like _________________________ • Can’t be tied down to a orbit like a planet • Instead scientist show where an electron is likely to be a any one point in time • Forms an electron __________

17. Comparing the Particles • In the nucleus • Protons • Charge= ________ • Mass = ___________________ • Neutrons • Charge= ______ • Mass= ______________________ • Surrounding the nucleus • Electron • Charge= ________ • Mass= _______________________

18. Elements • Composed of only one type of _________ • Identity is based on ___________ number • Atomic number (___)- number of protons found in that atom (ID number for elements) • Elements are ordered in periodic table according to this number • Mass Number (___)- mass of atom in atomic unit • Really the mass of the __________________________ • Electrons are so tiny that they don’t count

19. Calculating pne (Ground State) • # of protons= __________________ • # of electrons= _________________ • # of neutrons= _______________________________

20. Isotopes • Different forms of the same atom type • Differ by number of ____________ (so therefore differ by mass as well) • Isotope names- element name – mass number Lithium-6 Lithium-7 Lithium-8

21. Ions • Atoms that lose or gain ___________ form ions • Ions have a charge • Cation- ion with a ____________ charge • Anion- ion with a _____________ charge

22. Cations • Forms when atoms _________ electrons

23. Anion • Forms when atoms __________ electrons

24. Naming Ions • Cations • “Name of the element” ion • For example, Ca+2 is calcium ion • Anions • “Name of the element with ending changed to –ide” ion • For example Cl- is chloride ion

25. Calculating pne (Ions) • # of protons= atomic number • # of electrons = • atomic number – charge for cations • Atomic number + charge for anions • # of neutrons= mass number – atomic number

26. Atomic Masses on the Periodic Table • Atomic masses on periodic table are an average of all naturally occurring ___________ based on their abundance

27. Calculating Atomic Mass Need Mass of each isotope Fractional abundance of each isotope (must change to fraction if given as %) For each isotope Multiple the mass and the fractional abundance Add all of the answers together to get the atomic mass

28. Dmitri Mendeleev Proposed period table (1869) Arranged elements according to ________________ Grouped elements by similar properties Left holes for undiscovered elements and predicted their properties

29. Germanium Prediction

30. Structure of Modern Periodic Table Elements are arranged by _____________________ Elements occur in rows (or _________)- 7 periods in all Elements occur in columns (or ___________________) with similar chemical properties- 18 in all ______________ law- elements can be organized into patterns in the table based on chemical and physical properties

31. Periodic Groups

32. Other Periodic Groupings

33. Where do they belong? • The two series actually belong in the table like this, but we put them at the bottom to save space

34. Metals, Nonmetals, and Metalloids • Metal • Good conductor of electricity • Malleable • Ductile • Shiny • Nonmetal • Poor conductor of heat and electricity • Often gas or dull, brittle solid • Metalloid • Properties in between the other two

35. Natural States of Elements Most occur as solids Br and Hg can occur as a liquid Other occur as gas

36. Natural States of Elements (cont) • Many elements can exist in different forms naturally • Carbon • Both graphite and diamond are carbon, the atoms are just arranged differently

37. Diatomic Elements • Element occurs naturally in pairs • 7 elements • Hydrogen (H2) • Nitrogen (N2) • Oxygen (O2) • Fluorine (F2) • Chlorine (Cl2) • Bromine (Br2) • Iodine (I2)