1. Ions Section 5.5

2. IONS An ion is simply a charged atom. Ions are formed as atoms lose or gain electrons to achieve stability. To figure out how ions form, we must first start with its Bohr – Rutherford diagram : Fluorine - atomic number 9 9p 10n +9p -9e 0 = Total charge of zero Protons = Atomic # = 9p Neutrons = Atomic mass – Atomic # = 19 – 9 = 10n Electrons = # Protons = 9e

3. This structure is not stable as it does not have a full valence shell. Valence shell – the outermost electron shell of an atom. To achieve a full valence shell, Fluorine must gain an electron. Fluorine - atomic number 9 9p 10n +9p -9e 0 = Total charge of zero

4. The ion formed is now stable because its valence shell is full. MORE EXAMPLES... 9p 10n +9p -9e 0 = total charge of zero 9p 10n +9p -10e -1 = total charge of negative 1 Gain of an electron Fluorine atom (unstable)Fluoride ion (stable) -

5. Is it easier to gain two electrons or lose 6? 8p 8n Oxygen – atomic number 8 +8p -8e 0 = total charge of zero Gain two Gains two electrons 8p 8n +8p -10e -2 = total charge of neg 2 2-

6. Is it easier to gain six electrons or lose 2? 12p 12n Magnesium – atomic number 12 +12p -12e 0 = total charge of zero Lose two Loses two electrons 12p 12n +12p -10e +2 = total charge of plus 2 +2

7.  Metals always form positive ions (they give away their electrons to become stable).  Non-metals always form negative ions (they accept electrons to become stable).  Exception is noble gases because they do not form ions (they’re already stable!)  Remember, being “stable” means having a full valence shell.