Multiple Choice
Which of the following is an invalid listing within an electron configuration?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which noble gas is used as the core in the electron configuration of ruthenium (Ru)?
A
Kr
B
Ne
C
Ar
D
Xe
Verified step by step guidance1
Understand that the electron configuration of an element can be written in a shorthand form using the electron configuration of the nearest noble gas preceding it in the periodic table. This noble gas is called the 'core' or 'noble gas core.'
Identify the atomic number of ruthenium (Ru), which is 44. This tells us ruthenium has 44 electrons.
Look at the noble gases and their atomic numbers: Ne (10), Ar (18), Kr (36), Xe (54). We want the noble gas with the largest atomic number less than 44.
Since krypton (Kr) has 36 electrons, which is the closest noble gas with fewer electrons than ruthenium, it will be used as the core in the electron configuration of Ru.
Therefore, the electron configuration of Ru can be written starting with [Kr], followed by the electrons that come after krypton to complete the configuration for ruthenium.
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