Concept 1 Notes - Stability and Bonding.pptx

Chemistry

1. Combining Elements Most elements are not found by themselves in nature Usually they are found combined with other elements Compound : Two or more elements chemically combined The properties of a compound are very different from the properties of the elements that make up the compound Ex. Na and Cl are very different from NaCl

2. Chemical Formulas Chemical formula – used to tell what elements and how many of each element are in a unit of a compound Examples: H 2 O – water; contains 2 atoms of hydrogen and 1 atom of oxygen NH 3 – ammonia; contains 1 atom of nitrogen and 3 atoms of hydrogen O H H N H H H

3. Forming Compounds Why do elements form compounds? To be STABLE! All elements want to be stable. Octet Rule : Atoms will gain, lose, or share electrons in order to have 8 electrons in their outer energy shell Stability = full/complete outer energy level of valence electrons. 8 for every element except Hydrogen and Helium

4. Forming Compounds Sodium has 1 valence e - If it loses that 1 e - its outermost energy level will be FULL and it will be STABLE Chlorine has 7 valence e - If it gains 1 e - its outermost energy level will be FULL and it will be STABLE This is how the bond happens to form NaCl (table salt)

5. Would elements ever not benefit from forming compounds? YES if they are already stable  which the noble gases are! This is why noble gases are nonreactive. Their outermost energy levels are already full!

6. Would elements ever not benefit from forming compounds? YES if they are already stable  which the noble gases are! This is why noble gases are nonreactive. Their outermost energy levels are already full!

7. Bonds When atoms gain, lose or share electrons in order to become stable, they form chemical bonds Chemical bonds : a force that holds atoms together in a substance There are many types of bonds that can form, and not all bonds are created equal. We will start by looking at ionic bonds. Ionic bonds : when atoms transfer electrons in order to be stable. Usually between a metal and a nonmetal Results in the formation of ions

8. Ionic Bonds Ions : atoms or molecules that have a charge due to having lost or gained electrons Cations : positively charged ions; atoms or molecules that have lost e - Usually metals

9. Ionic Bonds Ions : atoms or molecules that have a charge due to having lost or gained electrons Cations : positively charged ions; atoms or molecules that have lost e - Usually metals Magnesium has 2 valence e - , so it will lose those 2 e - in order to be stable , creating a cation with a +2 charge = Mg +2

10. Ionic Bonds Ions : atoms or molecules that have a charge due to having lost or gained electrons Cations : positively charged ions; atoms or molecules that have lost e - Usually metals Magnesium has 2 valence e - , so it will lose those 2 e - in order to be stable , creating a cation with a +2 charge = Mg +2 Anions : negatively charged ions; atoms or molecules that have gained e - Usually nonmetals

11. Ionic Bonds Ions : atoms or molecules that have a charge due to having lost or gained electrons Cations : positively charged ions; atoms or molecules that have lost e - Usually metals Magnesium has 2 valence e - , so it will lose those 2 e - in order to be stable , creating a cation with a +2 charge = Mg +2 Anions : negatively charged ions; atoms or molecules that have gained e - Usually nonmetals Oxygen has 6 valence e - , so it will need to gain 2 e - in order to be stable , creating an anion with a -2 charge = O -2

12. Ion Examples: Example #1: What ion will Lithium form? Lithium has 1 valence e - , so it will lose that 1 e - in order to be stable , creating a cation with a +1 charge = Li +1

13. Ion Examples: Example #2: What ion will Nitrogen form? Nitrogen has 5 valence e - , so it will need to gain 3 e - in order to be stable , creating an anion with a -3 charge = N -3

14. Ions Elements in the same group have the same number of valence e - Because of this, elements in the same group will form ions the same way Ex. All elements in group 1 have 1 valence electron, so all of them will lose 1 e - to be stable, therefore forming an ion with a +1 charge This charge is called the oxidation number Will form Li +1 Will form Na +1 Will form K +1

15. Oxidation Numbers Oxidation numbers : the charge of an ion within a compound Written as a superscript to the right of the symbol Group 1 elements have 1 valence e -  +1 charge Group 2 elements have 2 valence e -  +2 charge Skip groups 3-12 transition metals Group 13 elements have 3 valence e -  +3 charge Group 14 elements have 4 valence e -  +/ - 4 charge Group 15 elements have 5 valence e -  -3 charge Group 16 elements have 6 valence e -  -2 charge Group 17 elements have 7 valence e -  -1 charge

16. Electron Dot Diagrams Because we really only care about the valence e - when using drawings to show how bonds will form, we will know learn a new and simplified diagram to show what elements will do when they form a bond  Electron Dot/Lewis Dot Diagrams

17. Electron Dot Diagrams Because we really only care about the valence e - when using drawings to show how bonds will form, we will know learn a new and simplified diagram to show what elements will do when they form a bond  Electron Dot/Lewis Dot Diagrams

18. Electron Dot Diagrams When drawing, the nucleus is represented by the atomic symbol . Determine the number of valence electrons (from group #) Represent the valence e- by drawing the amount of dots around the chemical symbol. Note : Fill one side at a time before you pair electrons up!! N Ex. Nitrogen

19. Practice Time! Hydrogen Carbon Fluorine Phosphorous H C F P

20. Using Electron Dot Diagrams to show Bond Formation Draw the electron dot structures of the elements. Transfer electrons (using an arrow) from the metal to the nonmetal . Add elements as needed. Continue transferring until all atoms are stable . Write the chemical formula using subscripts to show how many of each element were needed.

21. Using Electron Dot Diagrams to show Bond Formation Example #1 : What compound will form between Sodium and Chlorine? Na Cl NaCl

22. Using Electron Dot Diagrams to show Bond Formation Example #2 : What compound will form between Aluminum and Chlorine? Al AlCl 3 Cl Cl Cl

23. Practice Time! Potassium and Chlorine Magnesium and Fluorine Aluminum and Nitrogen Magnesium and Phosphorous Use electron dot structures to write chemical formulas for the following combination of elements:

24. Practice Time! Key Use electron dot structures to write chemical formulas for the following combination of elements: Potassium and Chlorine Magnesium and Fluorine KCl MgF 2

25. Practice Time! Key Use electron dot structures to write chemical formulas for the following combination of elements: Aluminum and Nitrogen Magnesium and Phosphorous AlN Mg 3 P 2