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Chapter 6

Chapter 6. The Periodic Table. The Periodic Table. Development of the Periodic Table: About 70 elements were discovered before the 1880s Dmitri Mendeleev first listed elements in a systematic, organized way. He arranged atoms by their properties and in order of atomic mass.

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Chapter 6

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  1. Chapter 6 The Periodic Table

  2. The Periodic Table • Development of the Periodic Table: • About 70 elements were discovered before the 1880s • Dmitri Mendeleev first listed elements in a systematic, organized way. • He arranged atoms by their properties and in order of atomic mass. • Mendeleev constructed the first periodic table. • He left blank places for unknown elements. • Henry Moseley determined atomic # and arranged elements by this instead of atomic mass.

  3. The Modern Periodic Table • Each element is represented by its symbol and atomic number placed in a square • The horizontal arrangement of elements are called periods. • Periodic Law—when the elements are arranged in order of increasing atomic number, there is a repeated pattern of physical and chemical properties.

  4. The Modern Periodic Table • Group—a vertical arrangement of atoms. • The elements in any group have similar chemical and physical properties. • Each group is identified by a number and letter A or B.

  5. The Modern Periodic Table • Group A elements are known as representative elements. • Representative elements are broken into 3 classes. • Metals—high electrical conductivity and luster • Alkali metals—Group 1A • Alkaline Earth Metals—Group 2A elements • Most non-representative elements are also metals

  6. The Modern Periodic Table • Nonmetals—occupy upper right corner of the periodic table. • Nonlustrous and poor conductors of electricity. • Some are gases, some are solids • 2 nonmetal groups have special names • Halogens—group 7A (ex. chlorine & bromine) • Noble gases—group 8A (or group 0) • Inert gases—they do not undergo chemical reactions

  7. The Modern Periodic Table • Metalloids—elements with properties that are intermediate between metals and nonmetals. • A heavy line divides metals from nonmetals. • Most elements that border this line are metalloids.

  8. Periodic Trends • Periodicity—the quality of occurring at regular intervals • The periodic table arranges the elements based on the periodic nature of their chemical & physical properties. • Trends we’ve studied so far include: • Electron configurations • Atomic #

  9. Atomic Size • Atomic Size: size of elements is difficult to define because of atomic orbital shapes. • Atomic Radius— ½ the distance between the nuclei of 2 bonded atoms.

  10. Atomic Radius • Measured in picometers (pm) • 1pm = 1 x 10-12 m • Down a group, atomic radius increases. • Nucleus increases & e- occupy outer orbitals • Across a period (left to right), atomic radius decreases • Electrons enter the same energy level • The protons & electrons are pulled to each other, so the size decreases.

  11. Ionization Energy • Ionization Energy—the energy required to remove an electron from an atom. • 1st ionization energy—the energy needed to remove the 1st e- from a neutral atom. • Na  Na+ + e- • 2nd ionization energy—the energy needed to remove 1 e- from the 1+ ion. • Na+ Na2+ + e-

  12. Ionization Energy • Down a group, ionization energy decreases • The outer e- are further from the nucleus and are easier to remove. • Across a period (LR), ionization energy increases • With more protons and electrons, the attraction is stronger.

  13. Ionic Size • Positive ions (cations) are smaller than their neutral atom. • They lose the outer shell of electrons • Negative ions (anions) are larger than their neutral atom. • More electrons reduce the attraction to the nucleus. • Down a group, ionic size increases • Across a period(LR), • Cation size decreases • Anion size decreases

  14. Electronegativity • Electronegativity—the tendency for one atom to attract electrons when bonded with another atom. • Measured in Paulings • Down a group, electronegativity decreases • Across a period (LR) electronegativity increases

  15. Periodic Trends Cation Size Anion Size All arrows show increasing Atomic Radius Density Ion Size Ionization Energy Solubility Electronegativity

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