1440Ch02Trans - Chapter 2 Atoms, Molecules, and Ions...

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Unformatted text preview: Chapter 2 Atoms, Molecules, and Ions Chapter 7 Periodic Properties of the Elements Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton. Daltons Atomic Theory Elements made of tiny particles called atoms. All atoms of a given element are alike, but atoms of one element differ from atoms of other elements Compounds are formed when atoms of different elements combine in fixed proportions. Chemical reaction involves a rearrangement of atoms. No atoms are created or destroyed or broken apart in a reaction. Atoms are indivisible . Structure of the Atom Cloud of electrons (e ) Diameter of atom = 10 10 m Diameter of nucleus = 10 15 m Nucleus: protons (p + ) neutrons (n) Electrons, protons, and neutrons are subatomic particles. Particle Relative Charge Mass (amu) Proton +1 1.007 Neutron 1.009 Electron 1 0.0005 Symbols of Elements Elements are symbolized by one or two letters. Atomic Number All atoms of the same element have the same number of protons: The atomic number (Z) Atomic Mass The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom. Atomic Weight (Mass) Actually average atomic weight (mass) Units...atomic mass units (amu) 1 amu = one-twelfth the mass of carbon-12 atom 1 amu = 1.66 x 10 27 kg = 1.66 x 10 24 g Mass and abundance of each isotope determined by mass spectrometry (MS) Ave. Atomic Mass = (Mass isotope)(Fractional abundance)+etc. Isotopes: Atoms of the same element with different masses. Isotopes have different numbers of neutrons. 11 6 C 12 6 C 13 6 C 14 6 C Average Mass Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. Average mass is calculated from the isotopes of an element weighted by their relative abundances. Atomic Mass Average atomic mass for silicon given the masses and abundances of its isotopes: Isotope Mass(amu) Fractional Abundance 28 Si 27.98 0.9221 (92.21%) 29 Si 28.98 0.0470 (4.70%) 30 Si 29.97 0.0309 (3.09%) Avg. Atomic Mass = (27.98 amu)(0.9221) +(28.98 amu)(0.0470) +(29.97 amu)(0.0309) = 28.09 amu 14 14 14 Periodicity When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities. Periodic Table First created by Dmitri Mendeleev Columns = Groups or Families Rows = Periods A systematic catalog of elements. Elements are arranged in order of atomic number. Elements in the same group have similar chemical properties. Groups These five groups are known by their names. Groups in the Periodic Table Maingroup elements (Representative) A groups Alkali Metals (Group I A) Alkaline Earth Metals (II A) Halogens (VII A) Noble gases (VIII A) Transition metals B groups Inner transition metals Lanthanides Actinides Newest element: ununquadium (Uuq) News of the Week...
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1440Ch02Trans - Chapter 2 Atoms, Molecules, and Ions...

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