Chapter 2 Isotopes Atoms with the same atomic number but different mass numbers All atoms of same element have same number of protons o Can have different number of neutrons Hydrogen o Protium or just hydrogen 1 proton o Deutrerium 1 neutron o Tritium 1 proton and 2 neutrons Isotope Abundance Percent abundance number of atoms of given isotope total number of atoms of all isotopes of that element x 100 Atomic weight Average mass of a representative sample Atomic weight abundance isotope 1 100 x mass of isotope 1 abundance isotope 2 100 x mass of isotope 2 The atomic weight of an element is always closer to the mass of the most abundant isotope Periodic Table Metalloids element that has some physical characteristics of metal but some chemical characteristics of nonmetals o B Si Ge As Sb and Te Group 1A o Alkali metals o Solid at room temperature o All reactive o Only found in nature combined in compounds NaCl H2O Group 2A o Alkaline earth metals o React with water to form alkaline solutions Group 3A o Aluminum most abundant metal gallium indium and thallium are metals o Boron is metalloid Group 4A o Carbon nonmetal o Silicon and germanium metalloids o Tin and lead metals o More variation in properties o Form compounds wit analogous formulas CO2 SiO2 GeO2 PbO2 o Allotropes particular elements can exist in several different and distinct forms each having own properties Group 5A o Nonmentals nitrogen and phosphorous o Metalloids As and Sb o Metal Bi o Form analogous compounds N2O5 P4O10 o