1. Aim: how is a covalent bond formed
Do Now: in your notebooks explain in terms of electronegativity why you think in covalent bonding there is a sharing of electrons and not a transfer of electrons

2. Energy and bonding
Atoms form chemical bonds between each other to become more stable.
A chemical bond has stored energy
When a bond is broken energy is absorbed (taken in)
When a bond is formed, energy is released, and the compounds formed have lower energy
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4. Na + Cl  NaCl energy is released N2  N + N energy is absorbed
Energy and Bonding
Na + Cl  NaCl energy is released N2  N + N energy is absorbed
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5. Structural Formula
A structural formula is a formula that shows the arrangement of atoms in the molecule of a compound.
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6. Octet Rule in Covalent Bonding
In covalent bonding Atoms usually acquire a total of eight electrons, or an octet, by sharing electrons.
A covalent bond is either shown by one, two, or three lines
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7. Single Covalent Bond
A Single Covalent Bond consists of two atoms held together by sharing 1 pair of electrons (2 e-)
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8. Electron Dot Structure

9. Shared versus Unshared Electrons
A Shared Pair is a pair of valence electrons that is shared between atoms
An Unshared Pair is a pair of valence electrons that is not shared between atoms
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10. Chlorine
forms a
covalent
bond
with
itself
Cl2

11. How
will
two
chlorine
atoms
react? Cl Cl

12. Cl Cl Each chlorine atom wants to
gain one electron to achieve an octet

13. Cl Cl do to achieve an octet? What’s the solution – what can they
Neither atom will give up an electron –
chlorine is highly electronegative.
What’s the solution – what can they
do to achieve an octet?

14. Cl Cl

15. Cl Cl

16. Cl Cl

17. Cl Cl

18. Cl Cl
octet

19. Cl Cl octet circle the electrons for each atom that completes
their octets

20. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets

21. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
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circle the electrons for
each atom that completes
their octets

22. Cl Cl This is the bonding pair circle the electrons for
Copy
circle the electrons for
each atom that completes
their octets

23. Cl Cl It is a single bonding pair circle the electrons for
COpy
circle the electrons for
each atom that completes
their octets

24. Cl Cl It is called a SINGLE BOND circle the electrons for
each atom that completes
their octets

25. Single bonds are abbreviatedCl Cl
Single bonds are abbreviated
with a dash
circle the electrons for
each atom that completes
their octets

26. This is the chlorine molecule,Cl Cl
This is the chlorine molecule,
Cl2
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circle the electrons for
each atom that completes
their octets

27. Two hydrogen atoms, each with 1 electron,
Covalent Bonding in H2
Two hydrogen atoms, each with 1 electron, H .
Practice
can share those electrons in a covalent bond. H :
Sharing the electron pair gives each hydrogen an electron configuration analogous to helium. 2

28. Two fluorine atoms, each with 7 valence electrons,
Covalent Bonding in F2
Two fluorine atoms, each with 7 valence electrons, .. .. F . :
Practice
can share those electrons in a covalent bond. F : ..
Sharing the electron pair gives each fluorine an electron configuration analogous to neon. 2

29. The Octet Rule
In forming compounds, atoms gain, lose, or share electrons to give a stable electron configuration characterized by 8 valence electrons. F : ..
The octet rule is the most useful in cases involving covalent bonds to C, N, O, and F. 2

30. to write a Lewis structure for CF4.
Example
Combine carbon (4 valence electrons) and four fluorines (7 valence electrons each) C . F : .. .
Practice
to write a Lewis structure for CF4. : F .. C
The octet rule is satisfied for carbon and each fluorine. 4

31. Example
It is common practice to represent a covalent bond by a line. We can rewrite : F .. C .. C F .. : as 4

32. Double Covalent Bonds
Sometimes atoms attain noble gas configuration by sharing 2 or 3 pairs of electrons
A Double Covalent Bond is a bond that involves 2 shared pairs of electrons (4 e-)
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33. O2
Oxygen is also one of the diatomic molecules

34. O
How will two oxygen atoms bond?

35. O
Each atom has two unpaired electrons

36. O

37. O

38. O

39. O

40. O

41. O

42. O Oxygen atoms are highly electronegative.
So both atoms want to gain two electrons.

43. O Oxygen atoms are highly electronegative.
So both atoms want to gain two electrons.

44. O

45. O O

46. O O

47. O O

48. Both electron pairs are shared.

49. O O
6 valence electrons
plus 2 shared electrons
= full octet

50. O O
6 valence electrons
plus 2 shared electrons
= full octet

51. O O
two bonding pairs,
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making a double bond

52. O O = For convenience, the double bond can be shown as two dashes.
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53. This is the oxygen molecule,=
this is so cool!!
This is the oxygen molecule, O2

54. Triple Covalent Bond
A Triple Covalent Bond is a bond that involves 3 shared pairs of electrons (6 e-)
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55. Covalent Bonds
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56. Summary
In your notebooks explain why covalent bonds are formed. State the difference between a single, double and triple bond.
DO SUMARRY

57. General Rules
For molecules containing more than three atoms select a central atom. The central atom would usually be the less electronegative atom.
Hydrogen and group 17 elements are never central atoms.
Make sure all atoms have a full outer shell ( H=2 valence electrons, all other elements =8 valence electrons)

58. Create a Table
Molecular Formula
Dot Structure of Atoms Present
Dot Structure of Molecule
Structural Formula
Types of covalent bonds present

59. Practice Lewis Dot Structure
Group 1: H2 N2 O2
Cl2
Br2 I2
Group 2: F2
HCl
CH4
H2O
NH3
H2Se
Group 3: HF
CO2
NI3
CBr4
HCN
H2S