1. Bonding

2. Valence Electrons Neon Argon Radon
The electrons on the outside edge of the atom
This is where the action is- where bonding takes place
Atoms have no more than 8 valence electrons
Neon
1s22s22p6
Argon
1s22s22p6 3s23p6
Radon
[Xe]6s24f 145d106p6

3. Maximum Number of Electrons Max number of Valence Electrons
Energy Level (Shell)
Maximum Number of Electrons
Max number of Valence Electrons 1 2 8 3 18 4 32 5 50 6 72 7 98

4. Electron-dot diagrams can be used to give the number of valence electrons
The number of valence electrons is equal to the element’ group number or # -10
Group Group Group Group 14 Group 15 Group 17
                                                                  

5. iodine phosphorus gallium argon
Write the electron-dot symbols for the following elements:
iodine phosphorus gallium argon

6. The Octet Rule:
Atoms will combine to form compounds in order to reach eight electrons in their outer energy level.
Atoms with less than 4 electrons tend to lose electrons.
Atoms with more than 4 electrons tend to gain electrons.
Some atoms share electrons

7. Types of Chemical Bonds
Ionic bond - a transfer of one or more electrons from one atom to another
Forms attractions due to the opposite charges of the atoms
Covalent bond - attractive force due to the sharing of electrons between atoms
Some bonds have characteristics of both types and not easily identified as one or the other

8. Why do compounds form?
Atoms are trying to get 8 valence electrons
How do compounds form?
By ionic or covalent bonding
How can you tell if a compound is ionic or covalent?
By the types of elements in the compound

9. Ionic compounds form between metals and nonmetals

10. Covalent compounds form between 2 nonmetals

11. Note Question 4:
Indicate whether a bond between the following would be 1) Ionic 2) covalent
____ A. sodium and oxygen
____ B. nitrogen and oxygen
____ C. phosphorus and chlorine
____ D. calcium and sulfur
____ E. chlorine and bromine

12. Ions Atoms with extra electrons or missing electrons
Extra electrons give an ion a negative charge
Missing electrons give an ion a positive charge
If they have to choose, atoms would rather be stable than neutral.

13. How Does This Happen? Some atoms have a few too many electrons
Some atoms only need a few electrons

14. What do you do if you are a sodium (Na) atom?
Go look for an atom that wants the extra electron!

15. Now you are a sodium ion With 10 electrons
Just like neon, with 8 valence electrons
But you’re not neon
You’re not a plain sodium atom
But you’re happy!

16. You are now quite attractive... Electrically.

17. Ionic Bonding Attraction that holds oppositely charged ions together.
Formed by the transferring of electrons

18. Ions from Metal Ions
In ionic compounds, metals in 1, 2, 13 and 3-12 lose electrons to nonmetals
Metals lose electrons to achieve the octet arrangement in the next lowest energy level
The names of metal ions are the same as the elements
Metal ionic charge: +1, +2, +3, or +4

19. Ions from Nonmetals
In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals
Nonmetal add electrons to achieve the octet arrangement
Nonmetal ionic charge: -3, -2, or -1
The names of nonmetal ions end in -ide

20. Formation of Sodium Ion
Sodium atom Sodium ion Na   Na + + e ( = Ne) 11 p+ 11 p+ 11 e- 10 e- 0 1+

21. Formation of Magnesium Ion
Magnesium atom Magnesium ion Mg:  Mg2+ + 2e (=Ne) 12 p+ 12 p+ 12 e- 10 e- 0 2+

22. Fluoride Ion
unpaired electron octet     1 - F  + e F     (= Ne) 9 p+ 9 p+ 9 e- 10 e ionic charge

23. Charges on Ions in Group 1-17

24. Ions
A. Number of valence electrons in aluminum 1) 1 e- 2) 2 e- 3) 3 e- B. Change in electrons for octet 1) lose 3e- 2) gain 3 e- 3) gain 5 e- C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

25. Learning Check B 3
Give the ionic charge for each of the following: A. 12 p+ and 10 e- 1) 0 2) 2+ 3) 2- B. 50p+ and 46 e- 1) 2+ 2) 4+ 3) 4- C. 15 p+ and 18e- 2) 3+ 2) 3- 3) 5-

26. What If No One Will Give Up An Electron?
Atoms with less than 8 valence electrons can move close to each other and share their electrons
The electrons spend their time around both atoms.
And they lived happily ever after!

27. Ionic Bonding Ionic bond – attraction between a cation and an anion
Attraction of Na+ with Cl- forms NaCl ion pairs that aggregate into a crystal lattice

28. Features of Ionic Bonding
• Ion formation takes place by electron transfer
• The ions are held together by the electrostatic force of the opposite charges
• Reactions between metals and nonmetals
(representative elements tend to be ionic)

29. Ionic Compound Properties
brittle
high melting points
conduct electricity in molten state or when dissolved in water

30. Covalent Bonding Let’s look at the formation of H2: H + H H2
Each hydrogen has one electron in its valance shell
Both hydrogen atoms have an equal tendency to gain or lose electrons
Electron transfer from one H to another usually will not occur under normal conditions (No one will let go!)

31. Instead, each atom attains a noble gas configuration by sharing electrons

32. Covalent bonds form between atoms with similar tendencies to gain or lose electrons
Compounds containing covalent bonds are called covalent compounds or molecules
The diatomic elements have pure covalent bonds (totally equal sharing)

33. The Polar Covalent Bond
Ionic bonding involves the transfer of electrons
Covalent bonding involves the sharing of electrons
Polar covalent bonding - bonds made up of unequally shared electron pairs

34. Polar Covalent Bonding
The electrons spend more time with fluorine
This sets up a polar covalent bond
A pure covalent bond can only occur when both atoms are identical

35. Electronegativity
Electronegativity - a measure of the ability of an atom to attract electrons in a chemical bond
Elements with high electronegativity have a greater ability to attract electrons than do elements with low electronegativity
The difference in electronegativity determines the extent of bond polarity

36. Electronegativity and Bond Polarity
The most electronegative elements are found in the upper right corner of the periodic table
The least electronegative elements are found in the lower left corner of the periodic table

37. Know the trend! Which is more electronegative Boron or gallium?
Calcium or zinc?

38. Table of Electronegativities (on your worksheet)

39. Electronegativity and Bond Polarity
The greater the difference in electronegativity between two atoms, the greater the polarity of their bond
Which would be more polar, a H-F bond or H-Cl bond?
H-F … = 1.9
H-Cl … = 0.9
The HF bond is more polar than the HCl bond

40. Look at your handout
There is a chart in the lower right hand corner of the back
This gives the break-off points for deciding what type of bond you have between two atoms
If the difference is 0, Pure covalent
If the difference is ≤0.4, Nonpolar covalent
If the difference is , Polar covalent
If the difference is >1.7, Ionic

41. Using the table of electronegativites, classify the following bonds as ionic, polar covalent or nonpolar covalent.
BCl3
CS2

42. There is no sharp distinction between bonding types.
The positive end (or pole) in a polar bond is represented δ+ and the negative pole δ-.

43. Dipole Moments Consider HF:
– The difference in electronegativity leads to a polar bond.
– There is more electron density on F than on H.
– Since there are two different “ends” of the molecule, we
call HF a dipole.

44. We can show this in two ways:

45. Some covalent molecules will have polar bonds, but the molecules themselves will be nonpolar
The polarity of the bonds cancel each other out

46. Water Water is a very polar molecule
This accounts for some of water’s unusual properties.

47. Water dissolves ionic and polar substances

48. Water molecules hold on tightly to each other
This accounts for properties like surface tension

49. Water has a high heat capacity
Water is a liquid at room temperature, even though other compounds in its size range are gases