Electron Arrangement and Interactions

• How elements interact depends on electron arrangement and available spaces in the outermost region of an atom.

Electron Shells

• Electrons reside in energy levels, forming shells around the nucleus.
• The innermost shell holds up to two electrons and fills first.
• Hydrogen, with one electron, has one occupied spot in the lowest shell.
• Helium, with two electrons, completely fills the lowest shell.
• Hydrogen and helium are the only elements with just the lowest shell.
• The second and third energy levels can each hold up to eight electrons.
• Eight electrons arrange as four pairs, filling one position in each pair before completion.

Periodic Table and Shells

• Rows in the periodic table indicate the number of electron shells an element possesses.
• Elements in a row gain electrons from left to right, but not all shells are filled.
• The second row includes lithium (Li) to neon (Ne), occupying the first and second shells.
• Lithium has one electron in its outer shell, neon has eight, filling it entirely.

Chemical Bonds

• Atoms are most stable with filled outermost electron shells.
• Vacancies in outer shells lead to chemical bonds, interactions forming molecules.
• Atoms bond to fill outer shells, sharing, accepting, or donating electrons.
• Elements with low atomic numbers (up to calcium) follow the octet rule, needing eight electrons in their outer shell.

Ions

• An ion is formed when an atom has unequal numbers of protons and electrons, resulting in a net charge.
• Cations are positive ions formed by losing electrons.
• Anions are negative ions formed by gaining electrons.
• Sodium readily donates its single outermost electron, becoming a +1 charged sodium ion.
• Chlorine tends to gain one electron to achieve a full outer shell, becoming a -1 charged chloride ion.

Electron Transfer

• Electron transfer involves the movement of electrons from one element to another.
• A sodium atom donates its electron so that a chlorine atom can accept that electron to fill its shell, becoming chloride.
• Both ions then satisfy the octet rule and have complete outermost shells.
• The number of electrons is no longer equal to the number of protons, each is now an ion and has a +1 (sodium) or –1 (chloride) charge.

Learn about the relation between elements and how they interact with each other based on their electron arrangement and the available spaces in the outermost region of an atom. The number of electron shells an element possesses is indicated by rows in the periodic table.