2. If opposite charges attract, why are the negative electrons not attracted to the positive nucleus?

3. Electrons are always moving. Electrons have inertia in motion = momentum.

4. If electrons are always moving and they weigh very, very little, why don’t they get thrown away out of the atom?

5. Because of the electromagnetic force!

6. Forces inside the atom This force of attraction binds the electrons to the atom. The electromagnetic force becomes stronger as the distance between charges becomes smaller.

8. If opposite charges attract, how do the protons get attracted with the neutrons?

9. Because of the strong nuclear force!

10. Forces inside the atom Protons and neutrons in the nuclei of atoms are held together by the strong force.

12. If the atomic mass/weight is just the sum of the protons and neutrons, why are there decimal values for the atomic weight written on the periodic table?

13. Atomic Weight is an Average! It is the weighted average of the individual atomic weights, or mass numbers, of the isotopes.

14. Example Chlorine = 35.48 (atomic weight) Isotopes of Chlorine Chlorine-35 = 76% abundance Chlorine-37 = 24% abundance Σ(mass number x %abundance)

15. Example The mass of Isotope 1 is 6.015 amu and its abundance is 7.5% The mass of Isotope 2 is 7.016 amu with a 92.5% abundance. What is the average atomic mass? What is the element?

16. The Periodic Table

19. Johann Dobereiner (1829) Triads!

20. The elements in a triad had similar chemical properties and orderly physical properties. Calcium, Strontium, Barium Chlorine, Bromine, Iodine

21. John Newlands (1863) Octaves!

22. After arranging the elements in order of increasing atomic mass, certain properties repeated every 8th element.

23. Lothar Meyer (1867) Increasing atomic mass!

24. Dmitri Mendeleev (1869) “Father of the Periodic Table”

25. Both scientists left vacant spaces where unknown elements should fit.

26. Periodic Table, I am your Father. Dmitri Mendeleev (1869)

27. The weight must be wrong. Reclassify! Dmitri Mendeleev (1869)

28. Increasing atomic NUMBER! Henry Moseley (1913)

29. Through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements. He rearranged the elements in order of increasing atomic number.

30. Actinide and Lanthanide Series! Glenn Seaborg (1944)

31. He reconfigured the periodic table by placing the actinide series below the lanthanide series

32. Periodic Table Geography

33. George M. McKelvy, Ph.D.33 The Modern Periodic Table Columns of elements are called groups.

34. George M. McKelvy, Ph.D.34 The Modern Periodic Table Rows of elements are called periods.

35. The Alkali Metals 1 valence electron Highly reactive with water Form ionic compounds Do not occur in nature as pure elements (always in compounds)

36. Alkali-Earth Metals Have 2 valence electrons Reactive, but less reactive than alkali metals Are ductile, malleable and have a silvery luster

37. Transition metals… and inner transition metals Are less reactive than groups 1 and 2. Tend not to react in water. Are malleable and ductile, but still harder than group 1 & 2. Tend to be solids at room temperature. Have variable chemical properties Are good conductors of electricity and heat. Inner transition metals tend to be radioactive

38. Nonmetals Poor conductors of heat and electricity Often are found as gases or liquids, sometimes solids.

39. Halogens Are nonmetals highly reactive with metals- most reactive is flourine, lease reactive is astatine Mostly exist as gases or liquids (except At -solid) Have 7 valence electrons

40. Noble gases At room temperature, exist as gases. Are completely unreactive Have full s and p orbitals Are odorless, colorless, nonflammable

41. Metalloids Tend to be solids Have properties similar to both metals and nonmetals Tend to be semiconductors (which means they are useful for technological uses)

42. Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

43. Metals, metalloids (semi-metals) and non- metals

44. Properties of Metals Good conductors of heat and electricity: lots of mobile electrons to move energy and charge around Have luster (shiny) Are ductile (stretchable) and malleable (bendable) Solids at room temp. except for Hg

45. Properties of Metalloids Have properties of both metals and non-metals Some of them are semiconductors (like silicon) which behave sometimes as conductors and sometimes as insulators Solids at room temperature

46. Properties of Non-Metals Poor conductors of heat and electricity Can be solids, liquids or gases (contrary to popular belief not all non-metals are gases!) Are not ductile, malleable

47. Periodic Trends - Reactivity – how likely or vigorously an atom is to react with other substances – Usually determined by how easily electrons can be removed and how badly they want to take other atom’s electrons since it is the transfer/interaction of electrons that is the basis of chemical reactions

48. Periodic Trends - Reactivity Metals – Period: DECREASES from left to right – Group: INCREASES down a group WHY? The farther left and down the periodic table, the easier it is for elections to be given or taken away, resulting in a higher reactivity

50. Periodic Trends - Reactivity Non-metals – Period: INCREASES from left to right – Group: DECREASES down a group WHY? The farther right and up the periodic table, the higher the electronegativity, resulting in a more vigorous exchange of electrons