Bohr Models of Ions

1. Bohr Models of Ions

2. The purposes of the following notes are to help you: • learn to recognize the difference between a Bohr model for an atom and a Bohr model for an ion. • understand why ions form in the predicable way as seen on the periodic table.

3. Changing Protons, electrons and neutrons • We know that if we change the number of neutrons in an atom, we create a new isotope. • We also know that if we change the number of protons in an atom , we create a brand new element. • But what happens if we change the number of electrons in an atom?

4. Changing the electrons: • Because protons are positive and electrons are negative, an atom with equal numbers of protons and electrons is “electrically neutral.” • Having a different number of protons and electrons will produce something that is no longer electrically neutral. It can no longer be called in atom. • Now it will be called an ion.

5. Comparing protons and electrons (12 protons) + (12 electrons) =_________ (12 protons) + (11 electrons)=_________ (12 protons) + (13 electrons) =_________ 0 “neutral Atom” “Positive ion” +1 “negative ion” -1

6. But why do elements form ions? • To answer this we must look at the noble gases.

7. The Noble Gases • He • Ne • Ar

8. Noble Gases are “cool.” • Noble gases have the perfect number of electrons…that is they have a full outer shell or valence shell • All the other atoms have not enough electrons or too many electrons. • As a result, all of the other elements spend their time trying to imitate the “cool” noble gases by getting rid of or by chasing after extra electrons from other atoms. • When atoms gain or lose electrons they become ions. • Noble gases, since their valence shells are filled, don’t react with other elements and are said to be inert. Thus they will not form ions.

9. Example 1: Metals A) Lithium (Li) Lithium wants to give away 1 electron and look like Helium. If it does, it will turn into a Li+1 ion.

10. Example 1 Metals: B) Magnesium (Mg) Magnesium wants to lose two electrons and look like Neon. If it does it will turn into a Mg+2 ion.

11. Metal ions • All metals need to lose one or more electrons to become “cool” which means they will always form Positive ions called cations. LEP

12. Example 2: Non-metals • Fluorine (F) Fluorine wants to gain one electron to look like neon If it succeeds, it will turn into a F-1 ion

13. Example 2: Non-metals B) Phosphorus (P) Phosphorus wants to gain 3 electrons to look like Argon. When it does, it will become a P-3 ion.

14. Non-metals • All non-metals need to pick up one or more electrons to be cool like the noble gases. Thus they always form negative ions called anions. • GEN: Gain Electrons=Negative

15. Exercise: 1) Determine the type on ion that each of the following atoms wants to form • Al → Al+3 (positive ion) • Be • O • Br • Na

16. Exercise: • When a METAL meets a NON-METAL they form an Ionic Bond • When Na meets F: Na wants to give away 1 electron and become Na+1. F wants to take away 1 electron and become F-1. They exchange electrons and are now “cool” and they have opposite charges and opposite charges cancel.

17. Exercise B) When Mg meets O

18. Exercise: C) When Mg meets F:

19. Exercise: D) When Al meets Cl:

20. Exercise: D) When K meets S:

21. Assignment: • WB p63-64 Q# 1-14, 16 • Quiz next class: Bohr models of atoms vs ions.

22. Ionic Compounds

23. Writing Ionic Compound Formulas: • Binary Compound: a compound with only two types of elements in an ionic bond (metal and non-metal) Step 1: Metal is written first, non-metal is written second Step 2: Write the combining capacities (or charge) beside each ion as a superscript. Step 3: Flip flop the combining capacities for each element and remove the charges (signs +/-) from subscripts. Step 5: reduce the subscripts and remove any “ones”

24. Assignment: • Text p 188 practice problems 1 and 2

25. Naming Ionic Compounds Step 1: Metal name stays the same and is written first Step 2: Non-metal name is written second and ends with “ide”

26. Write the chemical name: • NaCl Sodium Chlorine →remove the “ine” from chlorine →add the “ide” to Chlor___. Becoming: Sodium Chloride

27. Write the chemical name: 2) MgF2

28. Write the chemical name: • K+1 and S-2

29. Assignment: • Text p 187 practice problems 1a-o

30. B) Elements with more than one combining capacity: How do you recognize these elements? Elements on the periodic table that have more than one charge • Roman numerals are included in the names of these ionic compounds to show the charge of the metal ion. • Examples: I, II, III, IV, V,

31. Write the name for FeCl2 Check for metal and nonmetal Check for multiple combining capacity If yes: use roman numerals in name If no: no roman numerals in name Reverse flip flop Check nonmetal charge Write name (metal (RN) non-metal-”ide”) Example 1:

32. Example 2: • Write the name for • FeCl3

33. Assignment: • Text p 190 and 191 practice problems

34. C) Charged Groups of Atoms:AKA Polyatomic ions Groups of atoms that tend to stay together and carry an overall charge . How do you recognize them in a formula for a compound? Recognized by three or more capital letters in a formula of a compound • Polyatomic ions are treated as a single ion • See data booklet sheet

35. C) Charged Groups of Atoms:AKA Polyatomic ions Formulas: If two or more polyatomic ions occur in a compound, then the chemical formula for the polyatomic ion is enclosed in parenthesis Naming: the names of polyatomic ions stay as they are seen in the data booklet. No changing of the ending is needed.

36. Example 1: • Write the formula and name for • Ca+2 and OH-1

37. Assignment: • Text p193 practice problems