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Lewis Dot DiagramsScience 10 Mr. Dawson
Energy in the atom • Charged particles called electrons surround the nucleus in regions called shells or energy levels
Second Row – (2nd energy level) ∙ ∙ ∙ ∙ ∙∙ ∙∙ ∙∙ ∙∙ Li Be∙ B∙ ∙C∙ ∙N∙ ∙O: ∙F: :Ne: ∙ ∙ ∙ ∙∙ ∙∙ ∙∙ Electrons are added one at a time starting at 12 o’clock then 3, 6, 9 o’clock. Electrons do not pair until the 5th electron which is back to 12 o’clock. After 8 electrons there are 4 pairs of electrons which means this valence shell is full. The next shell out will begin to fill. Electron in the valence shell are called valence electrons. Notice the number of valence electrons and the group number. (Do you see a relationship?)
Atoms of different elements have different numbers of electrons • Each shell is “full” before electrons move to the next shell. Sodium has to inner shells and the outer (valence shell). The 1st and 2nd shells (inside shells) are full and the 3rd shell (valence shell) has one electron. This one electron in the valence shell is called a valence electron.
The Periodic Table and Electron Dot symbols (Lewis Structures) • Period number: gives the number of electron energy levels (valence shell last one out) • Energy levels will fill in the following order: 2, 8, 8, 8….(valence shell last one out) • Group number: number of valence electrons (look at the second digit of the group number)
Trends: • Elements of the same group have similar properties because they have the same number of electrons in their outer shell. • The outer shell = valence shell • Electrons that occupy the valence shell are called valence electrons
Noble gas configuration • Group 18, the noble gases are the most stable of elements because their valence shell is full with electrons • Less energy required • During chemical changes atoms will change in electron configuration (the arrangement of valence) to try to get a full valence shell. • Metal atoms have few valence electrons and will lose valence electrons leaving a full inner shell (metals are born losers) • Non-metal atoms have larger number of valence electrons (close to full) and tend to gain electrons. (Non-metals are winners)