1. Objectives/Goals for Today
Discuss logistics of homework
Quiz over Chapter 1
Chapter two notes
Section 2.1
Section 2.2
Break
Section 2.3
Section 2.4
Section 2.5
Section 2.6

2. Chapter Two Atoms & The Periodic Table

3. Section 2.1 Atoms First

4. Atoms
Atoms are the smallest quantities of matter that still retain the property of that matter

5. A brief history
Democritus was the first to develop this idea of an atom in the 5th century
John Dalton was the first to formalize the idea of an atom with Dalton’s atomic theory
Known as the “father of atomic theory”
The word “atom” comes from the Greek word “atomos” meaning “uncuttable.”

6. Dalton’s Atomic Theory
All matter is made up of atoms
Atoms are indivisible
Atoms of the same element are identical
Atoms of one element are different than atoms of another element
Atoms come together to form compounds

7. Dalton’s Law of Multiple Proportions
If two elements can combine to create multiple compounds, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers
CO CO2
100 g of C g of C
133 g of O g of O

8. Section 2.2 Subatomic Particles & Atomic Structure

9. Discovery of the Electron
Late 1800s; discovered by J.J. Thomson

10. Discovery of the Electron
Thomson performed many experiments with variable electric fields and measured degree of reflection
Charge-to-mass ratio
1.76 x 108 C/g (C stands for coulomb)

11. Charge of an Electron Early 1900s; discovered by Robert Millikan
Oil Drop Experiment

12. Charge of an Electron
Millikan used Thomson’s charge-to-mass ratio to determine the mass of an electron

13. The Proton Atoms are neutral; need for a positive particle
Thomson believed in the plum pudding model

14. The Proton
Rutherford contested this with the Gold Foil Experiment

15. The Proton & The Nucleus
Rutherford proposed all of the atom’s positive charge in the core of atom called the nucleus

16. Proton vs. Electrons Protons: in the nucleus
Provide same charge as electrons, only opposite sign
Provide the mass of the atom (nearly 2000 times more massive than electrons)
Electrons: outside the nucleus
Provide the volume of atom

17. The Neutron Discovered by James Chadwick in 1932
Practically same mass as proton
No charge

18. Break
Be back in 5!

19. Section 2.3 Atomic Number, Mass Number and Isotopes

20. Element Symbols

21. Isotopes Not all atoms of a given element are identical
Most elements have 2 or more isotopes (atoms with same # of protons, different # of neutrons)

22. Isotopes Isotopes behave like each other Named after their mass number
Ex: U-235 (“Uranium two thirty five”)

23. Ions Atoms with charges (different # of electrons)
Positive ions called cations
Negative ions called anions

24. Practice
List the number of protons, neutrons, and electrons in the following elements:
Carbon-14 Iodine-128
An atom has a mass number of 114 and 66 neutrons. Write the isotope notation for this atom.

25. Section 2.4 Average Atomic Mass

26. Average Atomic Mass Mass of an atom in atomic mass units (a.m.u)
Based off of 1/12 of a carbon atom
Most elements are mix of isotopes in nature
Average Atomic Mass is reported

27. Practice
The atomic masses of two stable isotopes of copper, copper-63 and copper 65, are and amu, respectively. If copper-63 is 69.17% and copper-65 is 30.83%, what is the average atomic mass of copper?

28. Break!
Be back in 5!

29. Section 2.5 The Periodic Table

30. The Periodic Table Mostly metals (left of stair step)
Good conductors of heat/electricity
Non metals (right of stair step)
Poor conductors of heat/electricity
Metalloids/Semi-metals (on stair step)
Properties of both metal and nonmetal
B, Si, Ge, As, Sb, Te, Po, At

31. The Periodic Table Groups: vertical columns Periods: horizontal rows
Elements in the same group share similar chemical properties
18 groups
Periods: horizontal rows
Elements transition from metal to nonmetal across a period

32. The Periodic Table

33. Section 2.6 The Mole and Molar Mass

34. The Mole A unit of quantity (how much)
Mole = mol
1 mole = x 1023 “particles”
“particles” can be atoms, molecules, or formula units

35. Molar Mass
Molar Mass = the mass of ONE MOLE of a substance
g/mol

36. Molar Mass 1 mole of water = 18.02 grams
1 mole sodium chloride = g
1 mole helium gas = g

37. Molar Mass Molar mass is found by Listing elements in compound
Determining their mass found on periodic table
Multiplying by how many atoms there are
Adding these values
Ex: H2SO4

38. Conversions
How many molecules of magnesium chloride (MgCl2) are there in grams of magnesium chloride?
How many chlorine atoms are there in the same mass of magnesium chloride?

39. A helpful guide

40. Group Quiz
1)Describe the contributions of Thomson, Millikan, Rutherford, & Chadwick (include experiments where applicable) 2)Write the appropriate symbol for the following: Z=28, A=64 3)How many protons, neutrons, & electrons in 4)Rb-85(72.17%) is If the average atomic mass of Rb is , what is the atomic mass of Rb-87(27.83%). 5)Name 2 elements from each of the groups of the periodic table discussed today 6)How many grams is 5.30 x 1023 molecules of K2O? +3