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The periodic table

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课程笔记

History of the Periodic Table

  • Early tables arranged elements by atomic weight, but this didn't always match properties.
  • In 1869, Dmitri Mendeleev rearranged elements so that similar properties were in the same group.
  • Mendeleev left gaps for undiscovered elements and predicted their properties.
  • When new elements were found, they matched Mendeleev's predictions.

Modern Periodic Table

  • Elements are arranged by increasing atomic number (number of protons).
  • Each element has a chemical symbol (e.g., Na for sodium).
  • The atomic number is written above the symbol.

Groups and Periods

  • Columns are called groups; elements in the same group have similar properties.
  • Group 1 elements are alkali metals; they react vigorously with water.
  • Rows are called periods.
  • Metals are on the left of the bold line; non-metals on the right.

Metals and Non-Metals

  • Aluminium (Al) is a metal (left of bold line).
  • Carbon (C) is a non-metal (right of bold line).
  • Metals are good conductors of electricity; non-metals are poor conductors.

Advantages of Grouping

  • Similar properties in a group make it easy to predict properties of unknown elements.
  • For example, all alkali metals react similarly with water.

Bohr model of sodium atom (atomic number 11) showing electron configuration 2,8,1.

Na — Bohr model (2,8,1)11p12n

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练习题

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  1. 1.In the periodic table, elements are arranged in order of increasing:

    Easy
    • Aatomic number
    • Batomic weight
    • Catomic radius
    • Dnumber of neutrons
  2. 2.Which of the following statements about the periodic table is true?

    Medium
    • AElements in the same period have similar properties.
    • BElements are ordered by atomic mass.
    • CColumns are called groups and contain elements with similar properties.
    • DMetals are found on the right of the bold line.
  3. 3.What is the atomic number of iron (Fe)?

    Easy
    • A26
    • B56
    • C55
    • D30
  4. 4.Which of the following elements is a non-metal?

    Easy
    • AAluminium (Al)
    • BCarbon (C)
    • CIron (Fe)
    • DCopper (Cu)
  5. 5.Why did Mendeleev leave gaps in his periodic table?

    Easy
    • ATo make the table look balanced
    • BFor elements that had not yet been discovered
    • CBecause the atomic weights did not match
    • DTo separate metals from non-metals
  6. 6.Which of the following is a property of alkali metals (Group 1)?

    Easy
    • AThey are unreactive
    • BThey react vigorously with water
    • CThey are non-metals
    • DThey are gases at room temperature
  7. 7.Aluminium (Al) is a metal. Which of the following best explains why aluminium is a good conductor of electricity?

    Easy
    • AIt is a non-metal
    • BIt is a metal and metals are good conductors
    • CIt is in Group 1
    • DIt has a low atomic number
  8. 8.In the periodic table, what do the rows (periods) indicate?

    Easy
    • ASimilar chemical properties
    • BNumber of electron shells
    • CAtomic mass increasing
    • DNumber of neutrons

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