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Modern Periodic Table 5.2

Modern Periodic Table 5.2. The Periodic Law. In the modern periodic table, elements are arranged by increasing atomic number (number of protons) Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. This is called periodic law.

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Modern Periodic Table 5.2

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  1. Modern Periodic Table 5.2

  2. The Periodic Law • In the modern periodic table, elements are arranged by increasing atomic number (number of protons) • Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. This is called periodic law.

  3. PARTS OF THE PERIODIC TABLE • Period – horizontal row • Group – vertical columns; they are numbered 1 – 18 • Family – specific name describing one or more groups; ex: Column 18 is the noble gases • Elements in the same group have the same number of valence electrons (electrons in their outer shell)

  4. Atomic Mass • Atomic mass depends on the distribution of an element’s isotopes in nature and the masses of those isotopes. • The atomic mass in grams is extremely small, so scientists developed a unit based on the carbon atom • Atomic mass unit (amu) – equal to 1/12 the mass of a carbon-12 atom

  5. CLASSES OF ELEMENTS • Metals – left and center part of periodic table • Conduct heat and electricity, have luster, malleable, ductile • All are solid at room temperature (except mercury)

  6. CLASSES OF ELEMENTS • Transition elements – groups 3 – 12 • They are metals • Unpredictable reactivity and properties

  7. CLASSES OF ELEMENTS • Lanthanides – atomic number 57 – 70 a. Rare earth elements – less than 0.01% of the elements found on Earth

  8. CLASSES OF ELEMENTS • Actinides – Atomic number 89 – 102 • All radioactive • Only 90, 91, and 92 occur naturally

  9. CLASSES OF ELEMENTS • Nonmetals – right side of the periodic table • Very abundant in nature • Poor conductors of electricity and heat, brittle, many are gases

  10. CLASSES OF ELEMENTS • Metalloids – some properties of metals and some properties of nonmetals • They are found along the border between metals and nonmetals • They are semiconductors

  11. Exception to periodic law • Hydrogen is placed in group 1, even though it is a gas. • Hydrogen’s location is related to its valence electrons, not its physical properties • Elements in a group have similar properties because they have the same number of valence electrons • Valence electrons determine how reactive an atom is.

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