2. Valence and Periodic Table

The periodic table arranges elements in columns and rows based on their electron configuration.

Elements can have different counts in rows due to their electron shell structure.
- The first row: consists of hydrogen and helium, corresponding to the first electron shell (1s, which holds a maximum of 2 electrons).
- The second row: contains 8 elements that fill the electron configuration starting with 2s (2 electrons) followed by 2p (6 electrons).
- Filling order: follows 1s, 2s, 2p, then moves on to 3s, 3p.

The third row fills with 3s and then 3p electrons.
The fourth row begins with 4s, followed by 3d (transition metals that can hold up to 10 electrons), then 4p.
For the fifth row, it follows a similar pattern: 5s, 4d, then 5p.
The sixth row adds 6s, moving to 4f (the lanthanide series) containing 14 elements, then fills 5d and finishes with 6p.
The seventh row starts with the 7s electrons, followed by 5f (actinide series), then 6d, and finishes with 7p.
- Note: The 7p section is blank in natural tables because we've reached synthetic elements created in laboratories.

The expanded table includes lanthanide and actinide series within their respective positions based on electron configurations.
A peculiarity exists where a d shell electron fills before f shell electrons start filling in lanthanides and actinides.

The interactive tool ptable.com allows viewing elements according to their electronic structure and interactions.
Groups of elements:
- Alkali metals on the left (one electron in valence shell).
- Transition metals in the center (corresponding to the filling of d shells).
- Noble gases on the right (inert, do not bond easily).

Examining the orbitals reveals how each element's electronic structure contributes to its properties.
- Helium, a noble gas, has a full valence shell (2 electrons in the 1s subshell).
- Neon and Argon: have completed valence shells with 8 electrons in their outermost shell.
- Krypton has a full valence shell after filling its 4s, 3d, and 4p orbitals.

The octet rule states that elements tend to bond to achieve a full valence shell of 8 electrons (s and p subshells combined).
- This rule explains the behavior of bonding for elements that are not noble gases as they seek to achieve a stable electronic configuration similar to noble gases.