f. schifano, department of science bayonne high school bayonne, nj 07002
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Chemical Bonding: What and Why
F. Schifano, Department of ScienceBayonne High School
Bayonne, NJ 07002
•Five Days of Instruction and Practice
•Two Labs: Covalent vs. Ionic and Molecular Modeling (total 5 points)
•One Day of In-class Review: 16 March 2011
•Afterschool Session: 16 March 2011 3-5 pm
•Full-Unit Test: 17 March 2011 (13.5 points)
This Unit Will Be Nine Days Long
NJCCCS 5.2.12.B.1. (...chemical bonds are the interactions between atoms that hold them together in molecules or between oppositely charged ions.)
This Unit Addresses Key Standards
Explain how and why chemical bonds form
Distinguish between the types of chemical bond
Relate bond types to observable chemical properties
Indicate the three-dimensional structure of molecules
Key Skills
A chemical bond is a relationship between two or more atoms that involves the transfer or sharing of electrons.
What is a chemical bond?
Chemical reactions are the observable consequences of making and breaking bonds.
The formation or breaking of a bond results in a chemical change– an energy change and the production of a new product substance.
How are bonds related to chemical reactions?
Enthalpy is the potential energy stored in chemical bonds.
Chemical reactions release or absorb heat because the total enthalpy in the reactants is different than the total enthalpy of the products.
Enthalpy (H)
Mixtures are combinations of atoms that involve only physical jumbling rather than chemical bonding. ◦ Formed and separated by physical changes
What isn’t a chemical bond?
Intermolecular forces– weak, transient interactions between molecules control some physical, but not chemical properties.◦ Next unit we will focus on these.
What isn’t a chemical bond?
Atoms form bonds because in doing so they can rearrange their electrons in a way that makes them more stable.
Bonds are a way for atoms to achieve valence = 8. ◦ Hydrogen is stable at VAL=0 or VAL =2◦ Boron is stable at VAL = 6
Why do atoms form bonds?
Gilbert Lewis (ENG-1916) invented the structures to show on paper how molecules were bonded.
Lewis Structures
Lines represent covalent bonds. Each line counts as two electrons.
Dots represent unshared electrons. Unshared pairs are called lone pairs.
Reading Lewis Structures
Atoms have different needs to achieve stability so they will form different numbers and kinds of bonds.
Writing Lewis Structures
Elements Valence Number of Bonds
Number of Lone Pairs
Satisfied at this valence:
H 1 1 0 1
F, Cl, Br, I 7 1 3 8
O, S, Se 6 2 2 8
N, P 5 3 1 8
C, Si 4 4 0 8
B 3 3 0 6
Covalent Bond Behaviors
You should copy this slide to your formula sheet.
Write the highest bond order atom
in center
Link together all other high bond-order elements
Resolve all remaining bonds
so all VAL are fulfilled
Writing Lewis Structures
Write the highest bond order element in the center.
Attach all other high-bond order elements to this central atom by single bonds.
Show all missing bonds as empty lines. Use any available 1-bond order elements to
fill up empty bonds. If there are any empty bonds on adjacent
molecules, use multiple bonds to fill them.
Step-By-Step Lewis Structures
Write the Lewis structures of each of the following substances.
Practice
C H CH4 H3CCl
CO2 BF3 HCl NH3
CH2O NH2CH3 H2O H2S
CH3CH2OH PCl3 N2 H2C2
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