1. Chemical Bonding
Chapter 23

2. Valence Electrons
Chemical bonds result from the sharing or transfer of valence electrons
Valence electrons are those in the outermost energy level (think Bohr model)

3. Central concept
The interaction between atoms (bonding) = ONLY involves valence electrons
Think of the inner electrons as being “locked” tightly in filled energy level

4. Electron Dot Structures
Represent valence electron configurations of atom/ions of an element
Electrons are represented by dots and arranged in pairs around the elemental symbol along the four sides of a square
Can be anywhere from 1 to 8 dots around an atom

5. Electron Dot Structures
Electrons are arranged unpaired until they must be paired (only if there is more than 4 valence electrons) **He is the only element that does not follow this rule!

6. Electron Dot Structures
Why? Because we will use dot structures of atoms to show bonding.
Try dot structures for these:
Li Kr
Mg Ga
Si S

7. Electron Dot Structures
Li Kr Mg Ga Si S

8. Class Work Electron Dot Structures Oxygen Xenon Helium Hydrogen Tin
Calcium
Iodine
Aluminum
Radon
Neon
Potassium
Sulfur
Krypton
Barium
Strontium
Silicon
Arsenic

9. Valence Bonding Theory explains
How many atoms are connected
How these atoms are connected
Shape of the structure
IONIC = geometry of the structure
MOLECULAR = shape of the molecule
Strength of the bond (bond energy)
Ionic, nonpolar covalent, polar covalent

10. The Octet Rule
Atoms in compounds tend to gain or lose electrons (what’s this called?) to achieve the e- configurations of a noble gas
8 valence electrons!

11. Cation: atom with a + charge
The LOSS of valence e- produces a cation
produced from metals
lose 1, 2, or 3 electrons easily
atoms become cations to satisfy the octet rule

12. Anion: atom with a - charge
The GAIN of valence e- produces an anion
produced from nonmetals
gains 1, 2, or 3 electrons readily
atoms become anions in order to satisfy the octet rule

13. AGENDA May 13: Submit HW Notes – Ionic Compounds & Metals
CW – Properties of Ionic Compounds WS
HW – Types of Bonds Packet – highlight, complete all “Reading Checks”and “Picture This” in margins and 1& 2 on last page

14. Ionic bonds and properties of ionic compounds
An ionic compound is the result of the transfer of electrons from one set of atoms to another and consists entirely of ions
Ionic bond - forces of attraction that bind oppositely charged ions together
THEY MUST BE NEUTRAL!

15. NaCl and ionic bonding

16. Electron Dot Structures and Ionic Bonding
Let’s determine the correct ratio of atoms that will come together and form an ionic bond.
K & O
Li & Cl
Mg & N

17. Electron Dot Structures and Ionic Bonding
Then complete Ionic Bonding WS

18. Ionic bonds and properties of ionic compounds
Properties of ionic bonds
Conduct electricity
when dissolved in water
High MP due to
crystalline structure
Salts
Crystals at
room temperature
Net charge of zero
Composed of
Formula units

19. Properties of ionic compounds
1. Conduct electricity when dissolved in water (melt)
What needs to be present in order to conduct a current?
when ionic solids dissolve in water, they break apart into their component ions
these ions act as electrical conductors in water

20. Properties of ionic compounds
2. Salts - most ionic compounds are called salts because of their crystalline structure
Crystal - a solid that contains atoms, ions or molecules in a regular repeating three dimensional pattern

22. Notice Each Li+ ion is surrounded by four F- ions
Each F- ion is surrounded by four Li+ ions

23. Lithium Fluoride Again..

24. Properties of ionic compounds
3. High melting point due to crystalline structure
it will take a lot of energy to break these highly organized bonds

25. Properties of ionic compounds
4. Net charge of zero
anions and cations connect in a ratio such that the overall charge of the ionic compound is zero
Example: Al+3 + Cl-1 ==> AlCl3

26. Properties of ionic compounds
5. Composed of formula units
a formula unit represents a compound that is ionically bound
The lowest whole number ratio of ions represented in an ionic compound ex. NaCl instead of Na2Cl2

27. Let’s do this together…
Draw electron dot structures to illustrate the formation of the following two ionic compounds…
Magnesium Chloride
Aluminum Sulfide

28. Metallic Bonds
Definition: Consist of the attraction of the free-floating valence electrons for the positively charged metal ions.
Properties: Metallic bonds involve “moveable” electrons - this explains many of the properties of metals
conductivity
malleability
ductility

29. Metallic Bonds

30. AGENDA 25-APR: Submit HW Notes – Properties of Covalent Compounds
CW – Properties of covalent compounds WS
HW – pp KT #3, 7-9 RQ # 6, 17-22

31. Covalent bonds and properties of covalent compounds
Covalent bond - forms when electrons are shared between two atoms
H + H ==> H2 (H H)
Atoms can have SINGLE, DOUBLE, or TRIPLE covalent bonds

32. Covalent bonds
Atoms share electrons in a covalent bond so that each atom has 8 valence electrons & more stability

33. Covalent bonds

34. Covalent bonds and their properties
Properties of covalent bonds
Not very soluble
in water; poor/non
conducting
Share bonding
electrons
Low MP and BP
Can be gas,
liquid, or solid
at room temperature
Composed of
molecules
No charged
particles here!

35. Covalent bonds can be...
1. SINGLE - one pair of e- is shared between two atoms - shown as a dash (-) instead of two dots
F - F
dash is always used in covalent bonds to show shared electrons - NEVER for ionic bonds

36. Covalent bonds can be... Dots represent UNSHARED pairs of electrons
lone pairs (around the central bonding atom & affect molecular shape)
nonbonding pairs (around the bonded atoms)

37. Covalent bonds can be...
2. DOUBLE - two pair of e- is shared between two atoms
oxygen = common example
O2 - each O has 6 valence electrons so when the O2 bond is formed, it must share TWO pair of electrons to satisfy the Octet Rule
O = O

38. Covalent bonds can be...
3. TRIPLE - three pair of e- is shared between two atoms
nitrogen = common example
N2 - each nitrogen has 5 valence electrons so to fulfill the Octet Rule, three pairs of electrons must be shared
N N

39. AGENDA 28-APR: Submit HW Notes – Drawing Covalent Compounds
CW – Covalent bonding WS
HW – Covalent bonding WS; TEST NEXT MONDAY!

40. Drawing covalent bonds
Some atoms form single, double, or triple bonds when forming compounds to achieve an octet of electrons

41. Drawing covalent bonds
HCl: H + Cl ==> H Cl = shared pair
Shared pairs can be represented with a DASH
H-Cl HCl has THREE unshared pairs of electrons

42. Drawing covalent bonds
H2O: 2H + O ==> O H or O H
H H
Water has two shared pairs and two lone pairs of electrons

43. Drawing covalent bonds
Draw the following covalent compounds in your notebooks now:
NH3
CH4
CO2

44. AGENDA 29-APR: Submit HW Notes - Polarity
CW – Polarity of Molecules WS
HW – pp KT #10-13, RQ # 23-28; TEST MONDAY!

45. Ionic vs. Covalent bonds and electronegativity
What if one atom has a greater electronegativity than the other but not enough strength to pull the electron away all together (form an ionic bond)?
We land somewhere in the middle with
polar covalent bonds
non polar covalent bonds

46. Polar vs. Nonpolar Covalent Bonds
Electronegativtiy measures the nucleus’ ability to attract electrons
When bonding atoms approach each other a tug of war begins Example: HCl
Cl nucleus is stronger so bonding e- are closer to Cl Cl
:Cl H H

47. Non polar covalent bonds
Forms when atoms share electrons equally (like in the H2 example or CH4)
Each atom or BONDED atom has equivalent electronegativity values

48. Non polar covalent bonds

49. Polar vs. Non-polar http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm
Hydrogen – non-polar
Water - polar

50. AGENDA 30-April: Submit HW Notes – Molecular Geometry
CW – Shapes of Molecules WS #1-6
HW – Shapes of Molecules #7-12; TEST MONDAY!

51. Three dimensional chemistry
REMEMBER
electrons = same charge = repel each other
Lone pair electrons also repel
because electron pairs repel, molecules adjust their shape so that the valence electron pairs are as far apart as possible = VSEPR theory

53. Methane (tetrahedral, CH4)

54. Pyramidal (ammonia, NH4)

55. Bent (water, H2O)

56. AGENDA 1-April: Submit HW Molecular Geometry Activity
HW – Review Study Guide; TEST MONDAY!

57. 2-MAY:
Questions from Study Guide?
CW: Web Quest Review