1. Atomic Theory  The Periodic Table is the method of organization for all elements  Carbon-12 is the reference atom for the mass of all other atoms.  When an element is written with its name then a dash with a number, that number is the MASS NUMBER.  Mass number = number of protons plus the number of neutrons  When there are two numbers to the left of the element symbol, the top is the mass number and the bottom number is the atomic number  Atomic number = number of protons.

2. Atomic Mass Unit  Like the kilogram and the gram, an ATOMIC MASS UNIT, is a measurement of mass.  It is used for very small masses – mostly atoms and sub-atomic particles  An atomic mass unit is called a amu or just a u.  1 amu = 1/12 th of the mass of a Carbon-12 atom

3. Quick Review  The NUCLEUS of the atom is heavy and small  Contains the positively-charged PROTONS (which determine what element the atom is)  Contains the neutral NEUTRONS (the number of neutrons in an element can vary - ISOTOPE )  Neutrons and protons have approximately the same mass.  Outside the nucleus, the ELECTRONS are located in electron shells (sort of….)  The electrons are actually in a complex configuration that changes….but we often talk about a shell as a simplification.  Electrons are negatively charged.  Electrons have 0.05% the mass of a proton.  A neutral atom has the same number of protons and electrons. If they aren’t the same it is an ION

4. Historical Figures  Dimitri Mendelev created the first periodic table in order of increasing atomic mass.  This table was created using similar properties called families  Henry Moseley rearranged the periodic table in order of increasing atomic number.  He called this change the “ modern periodic law ”.

5. 3 main groupings  Metals: most elements are metals.  They are usually solid at room temperature (mercury is an exception) with a high luster  They readily lose electrons  Metalloids: are found between the metals and non-metals on the periodic table  They have some characteristics like metals  They will either gain or lose electrons  Non-metals:  They are usually dull and brittle.  tend to gain electrons in chemical reactions

6. Periodic Table

7. Diatomic Elements  There are 7 elements that never travel alone  These elements are called diatomic (2 atoms)  They are all non-metals  The bond between these pairs is a COVALENT bond and is weaker than the attraction to a Alkali metal or Alkaline Earth metal.  Diatomic Elements are Hydrogen (H), Nitrogen (N), Oxygen (O), Flourine (F), Chlorine (Cl), Bromine (Br), and Iodine (I)  Write these as H 2, N 2, O 2, F 2, Cl 2, Br 2 and I 2

8. Properties of Elements  Elements in a group have similar characteristics or properties.  This is because of the organization of the ELECTRONS  The periodic table will give you information about an element….but not always in the same place.  Hints:  Atomic number will always be a whole number (no + or -, no letters, no decimals).  Average atomic mass will usually be a number with a decimal  Other information might be oxidation numbers (important!) and electron configuration.

9. ElementElement SymbolAtomic NumberAverage Atomic MassNumber of Protons Hydrogen Beryllium Titanium Selenium Krypton

10. Groups can be labeled differently

11. Group Numbers  The ONE’s PLACE of the group number will tell you the number of VALENCE electrons  Valence electrons are the outer most electrons that make bonding between atoms possible.

12. Octet Rule  The octet rule is a chemical rule of thumb that states that atoms of main-group elements tend to combine in such a way that each atom has eight electrons in its valence shell  This is the same electronic configuration as a noble gas.  The rule is especially applicable to carbon, nitrogen, oxygen, and the halogens, but also to metals such as sodium or magnesium.

13. Duet Rule  The duet rule states that hydrogen and helium may have no more than two electrons in their valence shells.  In ionic bonds, Lithium and Beryllium will also loose electrons to follow the duet rule.

14. Elements and Ions  Elements are neutral atoms where protons equal electrons  Ions are atoms that are positively or negatively “charged” due to extra electrons or lost electrons.  Oxidation number : similar to the “charge” of an atom – refers to the charge the atom would have if its outer valence shell was full  by adding for non-metals (become negative)  Non-metals receive  By removing for metals (become positive)  Metals donate

15. Element Name# of ProtonsAtomic ## of ElectronsOxidation Number Fluorine 8 49 Krypton

16. Isotopes  Isotopes are atoms of the same element with different numbers of neutrons in the nucleus.  This means they have different masses.  The average atomic mass is the weighted average of all the isotopes of that element.  Example: Silicon is very abundant in the earth's crust. There is 78.4% of Si-28, 17.9% of Si-29, and 3.7% of Si-30.

17. Average Mass  Silver is all over the place, but it has varying atomic masses. Calculate the average atomic mass of a sample containing 23% Ag-107, 29% Ag- 108, 22% Ag-109, and 6% Ag-110.  Different types of tungsten exist in the earth’s crust. Calculate the average atomic mass of Tungsten which is 5% W-182, 29% W-183, 52% W- 184, and the rest is W-185.

18. Nuclear Reactions  Unlike chemical bonding and ionization, nuclear reactions involve the nucleus of the atom as it changes energy or mass.  The nucleus accounts for 99.99% of the mass of an atom  The nucleus accounts for 1/100,000 of the volume of an atom  Radioactivity is the energy/mass released by an unstable isotope.  When an radioactive isotope releases energy/mass it changes into a different element ( transmutation )

19. Decay Particles  Alpha decay (  ) is the largest and slowest of the three decay particles. It can be stopped by thick paper.  An alpha particle is 2 protons and 2 neutrons released from the unstable atom. (helium nucleus)  Beta decay (  ) is the medium size particle and can be stopped by 6 mm of aluminum  A beta particle is an electron.  Gamma decay (  ) is the smallest – it has no mass, it is a photon – and most penetrating needing lead to be stopped.

20. Fission and Fusion  Fission is the splitting of a heavy nucleus into lighter nuclei  Fusion is the combining of nuclei to form a bigger and heavier nucleus.  The consequence of fission or fusion is the absorption or release of energy.

21. Half-life  Radioactive isotopes are unstable and will release decay particles, changing into a new element.  The time it takes for half a sample to change is called the half-life.