25 Atoms of the same element can have different IsotopesAtoms of the same element can have differentnumbers of neutrons.
26 Weighted AverageThe relative atomic mass (also known as atomic weight and average atomic mass) is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance.
48 Li Na K Rb Cs Fr Alkali Metal Group 1A Very reactive metals. Do not occur freely in nature.Only one electron in their outer shell. (1 valence Electron)NaKRbCsFrMost reactive metal!!!!
49 Be Mg Ca Sr Ba Ra Alkaline Earth Metal Group 2A Very reactive Not found free in nature.Two electron in their outer shell.(2 Valence Electron)Magnesium and Calcium important elements in life.MgCaSrBaRa
50 B Al Ga In Tl Boron Family Group 3A Three electrons in their outer shell.(3 Valence Electrons)Aluminum is the most abundant metal in the Earth’s crust.AlGaInTl
51 C Si Ge Sn Pb Carbon Family Four electrons in their outer shell. Group 4A.Four electrons in their outer shell.(4 Valence Electrons)Consists of:One nonmetal (carbon)Two metals (tin and lead)Two metalloids (silicon and germanium).Except for water, most compounds in your body contain carbon.SiGeSnPb
52 N P As Sb Bi Nitrogen Family Group 5A. Five electrons in the outermost energy level.(5 Valence Electrons)They physical and chemical properties that are strikingly different.N and P make up fertilizer.PAsSbBi
53 O S Se Te Po Oxygen Family Group 6A. Six electrons in their outermost energy level.(6 Valence Electrons)Oxygen is the most abundant element in the earth’s crust.SSeTePo
54 FHalogensClThe halogens are five non-metallic elements found in group 7A of the periodic table.All halogens have 7 electrons in their outer shells.The halogens exist, at room temperature, in all three states of matter.BrIAt
55 He Ne Ar Kr Xe Rn Noble Gases The six noble gases are found in group 8A of the periodic table.These elements were considered to be inert gases.All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable.Colorless/Odorless GasesNeArKrXeRn
56 Electron Dot Diagram Lewis Diagram Symbol of the elementDots for Valence Electrons.(Outer most energy level Electrons)ClNeNaC