How many electrons are in the valence shell of
a) H?
b) Li?
C) He?
The correct answer and explanation is:
a) Hydrogen (H)
Hydrogen has an atomic number of 1, meaning it has one proton and one electron. Since it is in the first period of the periodic table, it has only one electron in its valence shell. The electron configuration of hydrogen is 1s¹, and the one electron is in the first (and only) shell, which is the valence shell. Thus, hydrogen has 1 electron in its valence shell.
b) Lithium (Li)
Lithium has an atomic number of 3, meaning it has three protons and three electrons. The electron configuration for lithium is 1s² 2s¹, indicating that the first shell is fully occupied with two electrons, while the second shell has one electron. The second shell is considered the valence shell for lithium. Therefore, lithium has 1 electron in its valence shell.
c) Helium (He)
Helium has an atomic number of 2, which means it has two protons and two electrons. The electron configuration of helium is 1s², which shows that both electrons occupy the first shell. In this case, the first shell, which is the valence shell for helium, is fully occupied with two electrons. Therefore, helium has 2 electrons in its valence shell.
Explanation
The valence shell is the outermost electron shell of an atom, which plays a crucial role in chemical bonding. The number of electrons in the valence shell determines how atoms interact with other atoms. Elements in the same group of the periodic table have similar valence electron configurations, which is why elements in a group tend to exhibit similar chemical properties. For example, elements in Group 1, such as hydrogen and lithium, typically have one electron in their valence shell, making them highly reactive. Helium, despite being a noble gas, has a full valence shell with two electrons, which gives it stability and makes it largely unreactive.