1. Introduction to Ions

2. Note : Up to this point, we have only discussed neutral atoms but you will now begin to learn about charged atoms (ions). The number of protons will NEVER change! If we change the number of protons we change the identity of the element. Ex: #protons = 6 Carbon # protons = 7 Nitrogen # protons = 8 Oxygen

3. Periodic Table To begin, you need to learn a couple of terms associated with the periodic table: ▫Group – column of the periodic table ▫Period – row of the periodic table Names of Groups: ▫Group 1A: Alkali metals ▫Group 2A: Alkaline earth metals ▫Group 7A: Halogens ▫Group 8A: Noble Gases – inert (do not form ions)

5. Ions REMEMBER: the neutral atoms always have equal numbers of protons and electrons because the charges cancel Proton (+) + Electron (-)= 0 For an atom to be charged, it must have different numbers of protons and electrons because the charges would no longer cancel. There are two types of ions: ▫Cations – positively charged; has fewer electrons than protons ▫Anions – negatively charged; has more electrons than protons.

6. Ions We can determine the charge of the atom based on its location on the periodic table. We look at the group number (column) and whether or not the atom is a metal or nonmetal. Metals form cations (lose electrons) and nonmetals form anions (gain electrons). Charges Groups 1A – 3A: the group number = the charge on the cation Example: Na is in group 1A so it has a charge of +1. Groups 5A – 7A: -(8 – the group number) = the charge of the anion Example: Chlorine is in group 7A so, -(8 – 7) = -1, thus it has a -1 charge.

7. Summary Only the number of electrons changes. If the atom gains electrons it has a negative charge and is called an anion. If the atom loses electrons it has a positive charge and is called a cation. Metals form cations. Nonmetals form anions. Group 1A = +1 Group 2A = +2 Group 3A = +3 Group 5A = -3 Group 6A = -2 Group 7A = -1 Group 8A = inert

8. Now lets practice!

9. What is the charge of a bromine ion? +1 +2 -2

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12. Does lithium form a cation or an anion? cation anion

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15. What is the charge of a magnesium ion? +1 +2 +3 -2

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18. Ions can have equal numbers of protons and electrons. True False

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