1. Chapter 6 Ionic and Covalent Bonds and Formulas

2. In our last unit… ATOM We talked all about the ATOM – Development of the atomic model, subatomic particles HOWEVER, we were only talking about atoms as one individual unit BOND In this unit we will be looking at how atoms combine (or BOND ) with other atoms to form compounds!

3. Electrons are Arranged in Shells – As we move down a family, the elements gain an electron shell. The first shell can hold up to 2 electrons. (Row/Period 1) The second and third shells can hold up to 8 electrons each. (Periods 2 & 3) The fourth and fifth shells can hold up to 18 electrons each. (Periods 4 & 5) The sixth and seventh shell can hold up to 32 electrons each. (Periods 6 & 7)

4. The Valence Electrons Give Atoms Their Properties The outer most shell is called the valence shell. The electrons in the valence shell are called the valence electrons. Atoms tend to gain or lose electrons to end up with a full valence shell. (8 e-) – Except H 2 and He which want a duet (2 e-) The number of valence electrons correspond to the digit in the ones place of the group number for elements in groups 1, 2, 13-18.

5. Electron Dot Diagrams Show Valence Electrons An electron dot diagram depicts an atom as its symbol and its valence electrons. – Ex: Carbon Carbon has four electrons in its valence shell (carbon is in group 14), so we place four dots representing those four valence electrons around the symbol for carbon.

6. Electron Dot Diagrams Show Valence Electrons Electrons are placed one at a time in a clockwise manner around the symbol in the north, east, south and west positions, only doubling up if there are five or more valence electrons. – Example: Chlorine (7 valence electrons b/c it is in group 17)

7. Paired and Unpaired Electrons As we can see from the chlorine example, there are six electrons that are paired up and one that is unpaired. When it comes to bonding, atoms tend to pair up unpaired electrons. – They do this in two ways that we will discuss in the chapter. A bond that forms when one atom gives an unpaired electron to another atom is called an ionic bond. A bond that forms when atoms share unpaired electrons between each other is called a covalent bond.

8. Ionic Bonding Ionic Bond – Bond between metal and nonmetal due to “electrostatic interactions” – Electrons are transferred from metal to nonmetal forming a positively charged metal ion (cation) and negatively charged nonmetal ion (anion)

9. 6.1 Ions and Ion Formation If one or more valence electrons are lost or gained, the balance between positive and negative particles in the atom is upset. – When an atom gains electrons, there are more negative charges in the atom than positive charges, so it becomes negative Example – Oxygen gains two electrons so it gains a charge of -2. – When an atom loses electrons, there are more positive charges in the atom than negative charges, so it becomes positive. Example – Magnesium loses two electrons so it gains a charge of +2.

10. Atoms Do What is Easiest For Them Atoms tend to do the least to gain a filled valence shell. – Elements in groups 1, 2 and 13 tend to lose electrons to wind up with a filled valence shell because it only involves the removal of 1, 2, or 3 electrons, not the addition of 7,6, or 5 electrons respectively. – Likewise for elements in groups 15,16, and 17, only in their case, they tend to gain 3,2, or 1 electrons, not lose 5,6, or 7 electrons respectively.

11. Examples Sulfur Sodium

12. Get Out Your Periodic Tables! What are the charges for groups 1, 2, 13, 15, 16, 17, and 18? – Group 1: – Group 2: – Group 13: – Group 15: – Group 16: – Group 17: – Group 18:

13. Atoms That Gain Or Lose Electrons Are Called Ions (we saw this last chapter!) An ion is formed when the number of electrons differs from the number of protons in an atom. – This is accomplished by gaining or losing electrons, not by adjusting the number of protons! – The charge of an ion is denoted as a superscript in the atom’s isotope notation. Ex: A Nitrogen ion:

14. 6.2 Ionic Compounds When an atom that tends to lose electrons comes in contact with an atom that tends to gain them, an electron transfer occurs. – As a result, two oppositely charged ions are formed. – The two oppositely charged ions are attracted to each other via the electrostatic attractions. IONIC BOND – These attractions create an IONIC BOND

15. Ionic bonds Result from a Transfer of Valence Electrons + -

16. All chemical compounds containing ions are called ionic compounds All ionic compounds are completely different from the elements from which they are made. Ionic compounds typically are formed from elements on opposite sides of the periodic table. For all ionic compounds, positive and negative charges must balance out. Ionic Bonds Result from a Transfer of Valence Electrons

17. Properties of Ionic Compounds Positive and negative ions come together to create an organized pattern called a lattice structure. An example of a lattice structure for sodium chloride

18. Properties of Ionic Compounds Ionic compounds tend to be brittle They have high melting and boiling points They tend to be soluble in water. – They can conduct electricity when dissolved in H 2 O Many of the physical and chemical properties of the components of the compound are changed when they bond.

19. 6.3 Writing Ionic Formulas +3 -2 +2 +1

20. +3 -2 6.3 Writing Ionic Formulas

21. Subscripts Show the Number of Atoms of Each Element in a Compound A subscript notes how many atoms of each element are in a subunit of a compound. 1 is NEVER used as a subscript. Ex: NaCl  1 Sodium atom:1 Chlorine atom Al 2 O 3  2 Aluminum atoms:3 Oxygen atoms. The subscripts determine how many of each atom is required to balance out the positive and negative charges from the ions.

22. Writing Formulas for Ionic Compounds We can use the charges of the ions in a compound to easily determine the formula of the compound. All you do is crisscross the charges to make them subscripts – Ex: magnesium nitride MgN +2-3 23 Don’t forget to drop the positive/negative signs once they’re subscripts!!

23. PRACTICE, PRACTICE, PRACTICE!! Write formulas for the following ionic compounds: Magnesium chloride Calcium bromide Sodium oxide Sodium chloride Potassium iodide

24. 6.4 Naming Ionic Compounds When naming ionic compounds, we take the name of the metal followed by the name of the non-metal, only we drop the last syllable and add –ide as an ending. – Examples: NaCl: Sodium Chloride Al 2 O 3 : Aluminum Oxide

25. PRACTICE, PRACTICE, PRACTICE! Write names for the given ionic compounds: CaCl 2 LiBr BeO AlCl 3 Ra 3 N 2

26. Polyatomic Ions There are some ions that are made of more than one element POLYATOMIC IONS – These ions are called POLYATOMIC IONS “poly” meaning more than 1, “atomic” meaning atoms  more than 1 type of atom in the ion Examples: (see chart for more) – Sulfate SO 3 2- – Hydroxide OH - – Nitrate NO 3 -

27. Naming Ionic Compounds with Polyatomic Ions The rules for naming polyatomic ions are the same rules for naming normal ionic compounds except you use the polyatomic ion name for the second word Example: MgSO 4 – magnesium sulfate LiNO 3 – lithium nitrate Ba(OH) 2 – barium hydroxide

28. Writing Formulas for Compounds with Polyatomic Ions You still crisscross the charges like you did for basic ionic compounds but you use the charges of the metal ion and the polyatomic ion Example: Barium phosphate

29. PRACTICE WITH POLYATOMICS! Name the compounds:Write formulas: RbNO 3 calcium phosphate NaHCO 3 lithium carbonate Mg(OH) 2 beryllium bicarbonate

30. Naming & Writing Formulas w/ Transition Metals Transition metals – all elements in groups 3- 12 and elements in groups 13, 14, and 15 below the stair step line – Can have more than one charge in ion form! Except Ag + and Zn 2+ When naming compounds involving transition metals, you need to include a roman numeral in parenthesis to indicate the charge of the ion

31. Writing Formulas w/ Transition Metals Writing Formulas of Compounds w/ Transition Metals : 1.Write the metal’s atomic symbol with the value of the Roman numeral as a positive charge 2.Write the value of the anion (negatively charged ion) with it’s charge 3.Crisscross the charges to get your formula Example: Lead (IV) hydroxide

32. Naming Compounds w/ Transition Metals Naming Compounds Containing Transition Metals: 1.Name the metal from its symbol 2.Determine the charge on the metal by “uncrossing” the charges on the positive and negative ions 3.Write the charge as a roman numeral in parenthesis 4.Write the name of the anion either as an element with an “–ide” ending or as the unchanged name of the polyatomic ion

33. Naming Compounds w/ Transition Metals Examples: CrCl 6 Fe(OH) 2 NiO

34. Covalent Bonding Covalent Bonds – Bonds in which e- are shared between two atoms – Most common type

35. 6.5 Covalent Bonds Result from a Sharing of Valence Electrons Another way for elements to form bonds is by sharing valence electrons. Elements that have a partially filled valence shell can complete them by sharing electrons with another element The mutual attraction for shared electrons is called a covalent bond (co- signifies sharing, -valent signifies valence electrons)

36. Shared Electrons Complete Shells F F

37. A substance made up of atoms which are held together by covalent bonds is a covalent compound. – They are also called molecules. 6.5 Covalent Bonds Result from a Sharing of Valence Electrons

38. Drawing Electron Dot Diagrams for Molecules Chemists usually denote a shared pair of electrons as a straight line. F Sometimes the nonbonding pair of electrons are left off of the electron dot diagram for a molecule

39. Nonmetals Tend to Form Covalent Bonds A covalent bond is formed when two atoms that tend to gain electrons come into contact with each other. Hydrogen tends to form covalent bonds because it has a fairly strong attraction for an additional electron. The number of covalent bonds an atom can form is equal to the number of additional electrons it can attract.

40. H Examples O H H H2H2 H2OH2O

41. More Examples CHH H H CH 4 NH 3 HH H N

42. Multiple Bonds Sometimes two atoms share more than just one pair of electrons. O2O2 OO CO 2 COO

43. (2 non-metals bonded together) Writing Formulas for Covalent Compounds (2 non-metals bonded together) 1.Write the symbol for the first element listed If there is a prefix on the first element, write the prefix value as a subscript attached to the first element’s symbol 2.Write the symbol for the second element listed If the prefix on the second element is “di-” or greater, write the prefix value as a subscript attached to the second element’s symbol

44. (2 non-metals bonded together) Writing Formulas for Covalent Compounds (2 non-metals bonded together) Examples: Selenium dioxide Carbon tetrachloride Nitrogen trihydride

45. 2 non-metals bonded together Naming Covalent Compounds (2 non-metals bonded together) Given the formula: 1.Write the names of the 2 elements 2.Attach a Greek prefix (see chart) to the beginning of the first element only if it has a subscript greater than or equal to 2 3.Attach a Greek prefix to the second element no matter what! 4.Change the ending of the second element’s name to an –ide ending

46. 2 non-metals bonded together Naming Covalent Compounds (2 non-metals bonded together) Examples: P 2 O 6 CO 2 NO

47. In review… Chemical Bonds – Force that holds atoms together – It’s all about the electrons (e-) Types of Chemical Bonds – Ionic Bond between metal and nonmetal due to “electrostatic interactions” Electrons are transferred from metal to nonmetal

48. In review… Covalent Bonds – Bonds in which e- are shared – Most common type Metallic Bonds – Atoms are bonded to one another (not to other elements) – Positive ions in a “sea” of negative charge (e-) – Example: Cu, Ag