ATOMS TO IONS Why atoms become ions How to draw Lewis Dot Structures How to determine the charge of an ion

Rules for being an atom! Use as little energy as possible Be stable Give or steal electrons to get a full outer energy level!! (either 2 or 8 electrons)

1. Use as little energy as possible H He Electrons stay far apart from each other Electrons travel in pairs before moving to the next energy level no more than 4 pairs /energy level (except level 1 has only 1 pair)

2. Be stable = full outer energy level H He Level 1: 1 pair max (2 electrons) Level 2: 4 pairs max (8 electrons) Level 3: 4 pairs max (8 electrons)

2. Be stable = full outer energy level 1H NOT FULL H 2He FULL  !! He

3. What about atoms that don’t have full energy levels? It can give up an electron Or It can gain 7 electrons Li Li is REACTIVE Li Which take “less effort?”

Metals GIVE electrons Li Li Metals GIVE electrons Lose an energy level Make CATIONS Have a positive charge is REACTIVE

Non-Metals TAKE electrons Cl Cl Non-Metals IONS TAKE electrons Have same # energy levels Make ANIONS Have negative charge is REACTIVE

LEWIS DOT STRUCTURES A shorthand way of showing valence electrons

Show only the VALENCE ELECTRONS! LEWIS DOT STRUCTURES Show only the VALENCE ELECTRONS!

X LEWIS DOT STRUCTURES How to draw Lewis Dot: Write the symbol for the element (the symbol has 4 sides) Determine the number of valence electrons for the element Use a dot to represent each electron Apply dots counterclockwise at 3; 12; 9 and 6:00; (If 2 or less apply at 3 and 9:00) The number of dots represents the number of valence electrons (7 in this example) X

BECOMING AN ION Easy to see in Lewis dot structure if atom has full energy level Easy to see charge of ion Every atom has 0 or 8 electrons in Lewis Dot to become an ion!! F atom F ION Stable for full valence shell also called noble gas electron configuration

BECOMING AN ION Li • Atom become ions TO BECOME MORE STABLE IONS are atoms that have gained or lost electrons to complete their energy levels Positive ions (cations) are formed when an atom loses electrons. Negative ions (anions) are formed when an atom gains electrons. Usually metals form cations & non-metals anions F atom F ION Li • Li +1 Stable for full valence shell also called noble gas electron configuration

CHARGE Always CHARGE = #p - # e- # of electrons that an atom GIVES or TAKES to have a full valence energy level example: Chlorine Needs to take one electron to have a full energy level CHARGE is NEGATIVE adding an e- gives Cl 18 electrons: Charge = # p - # e- 17 p – 18 e- = -1 charge

GROUPS & CHARGE Charge follows a pattern for the GROUPS Can you identify the pattern? +1 +2 +3 - 3 - 2 - 1

PRACTICE Draw the Lewis Dot for beryllium ION Draw the Lewis Dot structure for Be atom (#p=4, so #e-=4, but # valence e-=2) Be has 2 valence electrons, GIVE or TAKE? Give 2 or take 6 Which is “easier?” - GIVE AWAY 2 Charge = #p – # e- 4 - 2 (since you gave 2 away) = +2 HELPFUL HINT: + = it’s positive/good to give electrons; so give away 2 means +2 - = it’s negative/bad to take/steal electrons; so take 2 means -2

- CHARGE + PRACTICE: Na (atomic #11) and N (Atomic #7) Na Na+1 N-3 N

# electrons gained or lost To summarize: CHARGE Acts like METAL NON-METAL INERT Alkali metals Group I Alkaline earth metals Group 2 Group 13 Group 14 Group 15 Group 16 Halogens Group 17 Noble Gases Group 18 Lewis Dot for atom Li • • Be • • • B • • C • • N: • • • O • : F: : Ne: Charge on Ion + 1 + 2 + 3 + 4 - 4 - 3 - 2 - 1 # electrons gained or lost 1e- lost 2e- lost 3e- lost 4e- lost 4e- gained 3e- gained 2e- gained 1e- gained No change Example X+1 X+2 X+3 X+4 X-4 X-3 X-2 X-1 X Lewis Dot for ION [Li] +1 or Li+ Li+ [Be] +2 or Be+2 [B] +3 or B+3 [C] +4 or C+4 Ne -4 C -3 N -2 O -2 O -2 O -2 O -1 F