1. IONS

2. SO FAR...  So far we’ve discussed how to find the number of protons and neutrons in an element.  How many electrons do we have in an element?  WHAT DO YOU THINK?

3. ANSWER  If an element is neutral (does not have a charge), then the element has the same number of electrons and protons  All of the (+) from the protons is cancelled out by the same number of (-) from the electrons

4. IONS  In chemical reactions, atoms often gain or lose electrons (e-) to form charged particles  IONS : an atom or group of atoms that has an electric charge because it has lost or gained electrons  NOTE: From now on, I will abbreviate (e-) for electrons

5. VOCABULARY DISTINCTION  If an element has the same number of protons and electrons (neutral), it is called an atom  If an element has a different number of protons and electrons (has a charge), it is called an ion

6. IONS  Atoms start of with a neutral charge  In other words, they have the same number of e- and protons  Example: Oxygen (O) has an atomic number of 8  This means it has 8 protons  Therefore a neutral oxygen atom also has 8 e-

7. IONS  When an atom gains or loses electrons the atom forms a charge  Example: Neutral oxygen (O) atom has 8 protons and 8 electrons  In a chemical reaction, O gains 2 electrons  8 protons (+) and 10 electrons (-) gives a net (-2) charge

8. IONS  Formula for calculating ion charge:  #protons - #electrons = ion charge  How do we show an ion using a symbol?  Neutral atom is the normal atomic symbol  For example: Neutral oxygen = O  An ion shows the charge associated with the atom  For example: Oxygen with a -2 charge = O -2

9. IONS  Calculate the charge on the following ions and write out the ion symbol: 1. Chlorine (Cl) atom with 18 electrons 2. Aluminum (Al) atom with 10 electrons 3. Copper (Cu) atom with 27 electrons 4. Potassium (K) atom with 18 electrons 5. Sulfur (S) atom with 18 electrons

10. IONS  Answers: 1. Cl - 2. Al +3 3. Cu +2 4. K + 5. S -2  NOTE: When an ion has a (+1) or a (-1) charge, we only write a (+) or a (-)

11. ION TYPES  Definition of ions  Cation: an ion that has a positive charge  Anions: an ion that has a negative charge

12. IONS  Ions behave differently than the atoms from which they are formed.  Na (neutral sodium)  very reactive and will explode in pure water  Na + (sodium ion)  very stable (is in the table salt we eat)  Cations and anions combine together to form neutral compounds

13. AGAIN, LOOK AT YOUR PERIODIC TABLES  Group 1 (alkali metals): lose 1 e- to form (+1) charge  Group 2 (alkali earth metals): lose 2 e- to form (+2) charge  Group 7 (halogens): gain 1 e- to form (- 1) charge  Group 16: gain 2 e- to form (-2) charge  Group 15: gain 3 e- to form (-3) charge  Transition metals: lose different amounts of e-

14. HOW DO WE COMBINE THE SYMBOLS FOR IONS AND ISOTOPES  Previously, we looked at how to show the symbol for atoms that have a certain number of protons and neutrons  Today, we will combine this with the number of electrons also

15. EXAMPLE  How would you write the symbol for an atom that has 29 protons, 34 neutrons and 27 electrons?  Step 1: Find the symbol  Step 2: Number of protons goes in the bottom left  Step 3: Protons + neutrons goes in the upper left  Step 4: Charge (protons – electrons) go in the upper right

16. ANSWER Cu 63 29 +2

17. TRY THESE 1. An atom with 35 protons, 45 neutrons, and 36 electrons. 2. An atom with 12 protons, 13 protons, and 10 electrons. 3. An atom with 10 protons, 10 neutrons and 10 electrons.

18. TRY THESE  Write down the number of protons, neutrons and electrons for the following:  32 S -2 16  56 Fe +3 26  39 K + 19