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.

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

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

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 ”.

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

Periodic Table

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

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.

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

Groups can be labeled differently

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.

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.

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.

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

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

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.

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.

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 )

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.

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.

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.