A discrete energy level surrounding the atomic nucleus where electrons reside, with each shell (n=1,2,3,...) holding a maximum of 2n2 electrons.
Electrons live in 'floors' around the nucleus. Lower floors fill first.
Showing a random 20 of 50 problems.
Example 1
easy
Using 2n2, find the maximum capacity of shell n=5.
Example 2
challenge
An emission line forms when an electron drops from n=3 to n=2 in hydrogen. Is the photon emitted in this transition higher or lower energy than one from n=4 to n=2?
Example 3
hard
What is the shell configuration of a neutral iron atom (Z=26)?
Example 4
medium
How many electrons does O2− have, and what is its shell configuration?O²⁻: 10 electrons, configuration 2, 8 (isoelectronic with Ne)
Example 5
medium
A neutral chlorine atom has 17 electrons. Give its shell configuration and the outer-shell count.Cl: 2, 8, 7 — outer shell has 7 electrons
Example 6
medium
A neutral sodium atom has 11 electrons. Write its electron-shell configuration.Na: 2, 8, 1
Example 7
easy
Helium (2 electrons) fills which shell completely?
Example 8
hard
Why does adding a third shell to sodium (config 2,8,1) lower its ionization energy compared to lithium (2,1)?
Example 9
medium
How many electrons does a neutral nitrogen atom (Z=7) have in its outer shell?
Example 10
medium
How many valence electrons does carbon (Z=6) have?
Example 11
medium
Halogens like Cl (Z=17) and Br (Z=35) react similarly because each has how many outer-shell electrons?
Example 12
easy
What is the maximum number of electrons the first shell (n=1) can hold?
Example 13
medium
Compare the outer-shell configurations of lithium (Z=3), sodium (Z=11), and potassium (Z=19). Why are their chemistries similar?
Example 14
easy
How many electrons does a neutral beryllium atom (4 electrons) have in its outermost shell?
Example 15
medium
A neutral atom has the configuration 2, 8, 8. How many electrons does it have and what element is it?
Example 16
easy
Write the shell configuration of a neutral silicon atom (Z=14).Si: 2, 8, 4
Example 17
medium
Which element has the configuration 2,8,5?
Example 18
challenge
Potassium has 19 electrons. Its configuration is 2, 8, 8, 1 rather than 2, 8, 9. Explain why the fourth shell starts before the third is full.
Example 19
hard
Compare the electron shell arrangements of neon (Z=10) and argon (Z=18). Explain why both are chemically inert despite having different numbers of total electrons.
Example 20
medium
Why does the third shell appear to hold only 8 electrons in the configuration of argon (Z=18) even though 2n2=18?