Concept:The periodic table is arranged in periods (horizontal rows) and groups (vertical columns). Moving across a period changes the number of valence electrons, while moving down a group increases the number of electron shells.
Explanation:The valence electrons are the electrons found in the outermost shell of an atom.
Elements in the same period have the same number of occupied electron shells, but they do not have the same number of valence electrons.
As you move from left to right across a period, the atomic number increases by one proton and one electron.
This added electron goes into the same outermost shell, so the number of valence electrons increases progressively across the period.
For example, in Period 2, lithium has
1 valence electron, beryllium has
2, boron has
3, and so on up to neon with
8.
Elements in the same group have the same number of valence electrons, not the same number of shells.
Across a period, non-metallic properties generally increase, not decrease, because the atoms gain more valence electrons and become closer to completing an octet.
Therefore, the only correct statement about the periodic table is the one that says valence electrons increase progressively across a period.
Answer:Option B is correct: The valence electrons of the elements in the same period increase progressively across the period.