Questions and Answers
How many electrons can the second energy level hold?
8
What group do elements with full outer energy levels belong to?
Group 0 (Noble gases)
How did Mendeleev arrange the elements in his periodic table initially?
By atomic weight
What did Mendeleev do when he encountered elements that did not fit the patterns?
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How did Mendeleev account for undiscovered elements in his periodic table?
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What did Mendeleev do based on his confidence in his periodic table?
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How is the modern periodic table arranged?
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Which element type is placed in Group 0 (Noble gases)?
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Study Notes
Atomic Structure
- An atom has protons, neutrons, and electrons.
- The number of protons defines the element, while the number of neutrons defines the isotope.
- Isotopes are atoms of an element with a different number of neutrons.
Isotopes
- Examples of isotopes: ¹⁹F (9 electrons, 10 neutrons), ⁹Be (4 electrons, 5 neutrons)
- Atoms with the same number of protons but different number of neutrons are isotopes.
Ions
- Ions are atoms that have gained or lost electrons, resulting in an overall charge.
- Positive ions have lost electrons, while negative ions have gained electrons.
Noble Gases
- Noble gases are unreactive elements with a full outer energy level.
- Examples of noble gases: He, Ne, Ar, Kr, Xe, Rn.
- Boiling points of noble gases increase as their relative atomic masses increase.
- Boiling points of noble gases: He (-289°C), Ne (-246°C), Ar (-186°C), Kr (-153°C), Xe (-108°C), Rn (-62°C).
Electron Energy Levels
- Electrons exist in energy levels (shells) with a maximum number of electrons.
- Energy level capacities: 1st level (2 electrons), 2nd level (8 electrons), 3rd level (8 electrons).
- Elements with full outer energy levels are in Group 0 (Noble gases).
Periodic Table
- Mendeleev developed the first modern periodic table, arranging elements by increasing atomic weight.
- Mendeleev predicted the properties of undiscovered elements based on their position in the table.
- The modern periodic table is arranged by atomic number, not atomic weight.
Development of the Periodic Table
- Mendeleev's table was revolutionary, as he switched element positions to fit group patterns and predicted undiscovered elements.
- The modern periodic table has undergone changes, incorporating new elements and reorganizing the table by atomic number.
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