Topic: Atomic Concepts Aim: How are electrons arranged in an atom? Do Now: Take out HW Wkst – Element Symbols – pick 10 from top and 10 from bottom. Wkst – chart – fill in the information for the elements that do NOT have charges written next to them. HW:

What about electrons? Atomic # = ____ & ____ (for a neutral atom) # of neutrons = ____ The protons & neutrons are located ___ How are electrons arranged in the electron cloud?

Arrangement of Electrons Principal Energy Levels (PELs) Show distance from nucleus Up to 7 PELs Electrons in different shells have different energies. Low PEL# = close to nucleus = low energy High PEL# = far from nucleus = high energy

Atom with PELs n = 1, low energy n = 2, more energy n = 3, more energy than 2 Nucleus containing p & n

How many e- can each PEL hold? PEL (n) Max # of e- it can hold (2n2) 1 2 8 3 18 4 32

Electron Configuration How e- fill the PELs – how many e- are in each PEL Always start with PEL #1 (closest to the nucleus) & work your way out Once PEL #1 is full, the rest of the e- start to fill in PEL #2 till it’s full This info is on the PERIODIC TABLE!

Example Electron Configuration The 2 means there are 2 electrons in PEL #1. (PEL #1 is full.) The 4 means there are 4 electrons in PEL #2.

More Examples Magnesium & Zinc – for each… Atomic # # of e- e- config # of PELs occupied

Valence Electrons OUTERMOST e- These e- participate in chemical rxns with other atoms Give an element its chemical properties Last # of e- configuration How many valence e- does magnesium have? Zinc? Valence e-

X • • • • • • • • Lewis Dot Structures Shows VALENCE e- as DOTS around ATOMIC SYMBOL Symbol will have a MAXIMUM of 8 dots! Why? • • X • • • • • •

Examples Draw the Lewis structures for the following elements: Helium Sulfur Boron Nitrogen Neon