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Chemical Bonding: By: Ms. Buroker

Chemical Bonding: By: Ms. Buroker. Imagine getting onto a crowded elevator. As people squeeze into the confined space, they come in contact with each other. Many people will experience a sense of being too close together.

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Chemical Bonding: By: Ms. Buroker

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  1. Chemical Bonding:By: Ms. Buroker

  2. Imagine getting onto a crowded elevator. As people squeeze into the confined space, they come in contact with each other. Many people will experience a sense of being too close together. • When atoms get close enough, their outer electrons repel each other. At the same time, however, each atom’s outer electrons are strongly attracted to the nuclei of the surrounding atoms. • The degree to which these outer electrons are attracted to other atoms determines the kind of chemical bonding that occurs between the atoms.

  3. Chemical Bonding The force that holds two atoms together is known as a chemical bond.

  4. Compounds are formed from chemically bound atoms or ions Substances become more stable through chemical bonding, where 2 or more atoms are joined together by a simultaneous attraction.

  5. Bonding involves only the valance electrons. Na Cl

  6. Ionic Bonds Chemical Bonding that results from the electrical attraction between cations and anions is calledionic bonding.

  7. Ionic Bonds When you consider that for an ionic bond to form there must be a difference in charge between the ions, can you predict what two types of atoms allow this to occur?

  8. Ionic Bonds Non- Metals Metals Ionic Bonding occurs between metals and non-metals. This happens when metals lose an electron(s) (positive charged ion) and non-metals gain electron(s) (negatively charged ion). # of e- transferred = # of valance e-

  9. Ionic Bonds

  10. What is the Octet Rule? That atoms have a tendency toward a full valence shell with 8 e-.

  11. Why Do Atoms Bond In The First Place? Metals and non- metals react to form ionic compounds … electrons are transferred in order for both atoms to have a full valence shell. BUT!!!!!!!!!!!!!!! Sometimes two atoms both need to gain electrons and can have an attraction for the valence electrons. Sharing of electrons is another way in which atoms can bond!

  12. Covalent Compounds Covalent Bonds are those chemical bonds that result from the sharing of electrons.

  13. Ionic or Covalent In pure ionic bonds- electrons are completely given away to other atoms. In pure covalent bonds- electrons are totally owned by both atoms. It turns out … neither is completely true. In actuality, the truth lies somewhere in between. What makes the difference is how strongly the atoms of each element attract electrons.

  14. Electronegativity Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound.

  15. Electronegativity We can use Electronegativity values to determine whether a compound is ionically bound or covalently bound.

  16. Factors Determining Electronegativity When you subtract the electronegativity values of two atoms bound together … you use the value to determine what kind of bond you have. Non-polar covalent= 0-0.3 Polar Covalent Bonds= 0.3- 1.7 Ionic Bonds= 1.7- 3.3

  17. Covalent Bonds Polar- Covalent Bond: a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons. Non-polar covalent Bond: a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balance distribution of electrical charge.

  18. Molecules When compounds are covalently bonded, they form molecules.

  19. Molecular Formula When we have molecules … we have to write their formula, or what they’re made of. Molecular Formulas show the type and numbers of atoms combined in the covalently bonded compound.

  20. Covalent Bond Formation Everything in nature favors stability … covalent bonds form from a need for stability. There is a perfect distance apart the atoms need to be.

  21. Structural Properties The strength of covalently bound compounds … or molecules … depends on distance separating the atoms (size will affect this).

  22. Property Factors There are two factors we have to think about when dealing with bonds of any kind. 1.) Bond Length 2.) Bond Energy- the amount of energy it takes to break a bond.

  23. Property Factors What relationship can you observe on page 182 of your book where the bond lengths and bond strengths are listed? In general … the Longer the bond length … the weaker the bond!!! The opposite is true, shorter bond lengths tend to be stronger!!

  24. Electron Dot Structures and Lewis Structures We use electron dot structures as a way to symbolize the number of valance electrons an atom has. 6e- 7e- To put it simply, Lewis Structures are our way of explaining how atoms in a covalent bond share their valance electrons. It’s our best guess at what’s going on in the covalent bonding process.

  25. Lewis Structures Lewis structures use dots and/or dashes to represent bonding pairs of electrons and what we call lone pairs (electrons not directly involved in bonding.

  26. Drawing Lewis Structures Step 1: Sum the valence electrons from all the atoms Step 2: Draw the skeletal structure for the compound and bond all the terminal atoms to the central atom Step 3: Complete the octet for each atom Step 4: Place any left over electrons on the central atom Step 5: If there are not enough electrons to give the central atom an octet, try multiple bonds.

  27. Exceptions to the Octet Rule Be: 4e- B: 6e- Elements Beyond Period 2

  28. Structural Properties During the formation of an ionic compound, the positive and negative ions are packed into a regular repeating pattern that balances the forces of attraction and repulsion between ions … this is known as ionic crystal.

  29. Crystal Lattice We call this three dimensional arrangement of ions acrystal lattice.

  30. Crystal Lattice Properties High Melting Points and Boiling Points Hard, Rigid, Brittle They form Electrolytes Electrolytes are solutions that conduct electricity.

  31. Lattice Energy The energy required to separate one mole of the ions of an ionic compound . In other words … how strong are the forces holding the ions in place? There is a relationship between lattice energy and the interionic distance.

  32. Graphically Determine the Relationship Between the ionic radii and Lattice Energy LiF, LiCl, LiI Li+= 76pm, F-= 133pm, Cl-= 181pm, I- = 220pm LiF= -1032kJ/mol LiCl= -852 kJ/mol LiI= -761 kJ/mol X-axis= ionic radii Y- axis= lattice energy (use as a positive value)

  33. Lattice Energy Continued … The value of lattice energy is also affected by the charge of the ion …. The ionic bond formed from the attraction of ions with larger positive or negative charges generally has a more negative lattice energy.

  34. Predict … List the following compounds in order of increasing melting point in ○C: KBr KI KF KCl

  35. Ionic Bond = Ionic Compound Metals + Oxygen = Oxides Metals + Other Non-Metals = Salts Binary Compounds = 2 Elements Polyatomic … ex: polyatomic anions = made of many atoms # e- lost = # e- gained … overall charge must be 0

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