LFS103 Lecture Notes - Lecture 2: Fluid Balance, Octet Rule, Valence Electron
WEEK 2
2.1 Arranging electrons in Atoms
Electron Arrangement in Atoms: Every electron has a specific amount of energy
− Electron shells: Electrons of similar energy are grouped in an energy level called a shell
• The shells closest to the nucleus contain electrons with lowest energy
• 7 shells can orbit a nucleus
• Element periods = Number of shells they fill
• e.g. Ca fills 4 shells of electrons
• Capacity of the first four electron shells:
•
− The first twenty elements
• Fill 2 electrons into shell 1
• Fill 8 electrons into shell 2
• Fill 8 electrons into shell 3
• Fill 2 electrons into shell 4
Remember
2
8
8
2
Document Summary
Electron arrangement in atoms: every electron has a specific amount of energy. The first twenty elements: fill 2 electrons into shell 1, fill 8 electrons into shell 2, fill 8 electrons into shell 3, fill 2 electrons into shell 4. Valence electrons: the electrons in the outer shell. The first twenty elements: element group = number of valence electrons. Electron dot structure: shorthand system for designating the number of valence electrons. They consist of an element"s symbol with one dot for each valence electron placed around the elemental symbol. Ion: an atom that is electrically charges as a result of the loss or gain of electrons (p e-) Why atoms form ions: they want to fill up their outermost shell to make 8 electrons, octet rule: atoms adjust their valence electrons so they obtain the same electron configuration as a noble gas. When an atom loses its valence electrons, it has less negative electrons than positive protons.
