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Covalent Bonds

Covalent Bonds. Regents Chemistry U10 L01. What is a covalent bond?. Ionic Bonds involve a force of attraction that develops through… ELECTRON TRANSFER In covalent bond formation the bond is formed by ELECTRON SHARING

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Covalent Bonds

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  1. Covalent Bonds Regents Chemistry U10 L01

  2. What is a covalent bond? Ionic Bonds involve a force of attraction that develops through… ELECTRON TRANSFER In covalent bond formation the bond is formed by ELECTRON SHARING Both lead to the formation of the octet. However, The force of attraction in Covalent compounds involves each atom donating an electron to form ashared pair.

  3. ampicillin Covalent Bonds Many of the compounds we encounter in our daily Lives are covalently bonded compounds - Antibiotics - Food - Plants - Plastics - Clothing (Natural & Synthetic) - Biochemicals - What we breath and what we are - And so many other things its impossible to list them all!

  4. Molecular Bonds Covalent Bonds fall into several sub-categories: Non-polar Covalent Polar Covalent Coordinate Covalent Network Covalent We’ll start our discussion with non-polar covalent bonds

  5. Formation of a non-polar Covalent Bond (DEN < 0.4) 2 hydrogen Atoms Approach each other 1s orbitals overlap Each atom shares its Electron with the Other atom but… Each atom thinks the shared electrons are theirs alone!

  6. This sharing of electrons creates a new bond Between the atoms. Covalent Bond Electron density is concentrated in the region between The atoms. When 2 atoms approach the pt. of maximum attraction aSINGLE COVALENT BONDforms

  7. Non-polar If electron density is equally shared across both atoms One side of the molecule has no more electron density than the other side sono “poles “ develop This type of bond is called… Non-polar covalent

  8. Electronegativity differences Recall that bonds formed by atoms with electronegativity differences are greater than 1.7 are said to be IONIC 2 atoms with an electronegativity difference that is less than 1.7 will form a COVALENT bond When 2 atoms have an EN difference that is really low, Less than or equal to0.4these bonds are said to be… Non-Polar Covalent

  9. 3.2 2.1 Ionic Least Ionic - Most covalent Most Ionic – Least covalent Molecules with differences 0.5 or less are said to be Non-polar Covalent 0.5

  10. Electronegativity differences Between 0.4 and 1.7 there is a large number of Compounds having bonds known as Polar Covalent For example H2O 3.4 - 2.1 = 1.3 We’ll talk more about Polar compounds later.

  11. Unshared electron pairs Multiple atom electron sharing All atoms now have an octet In water, each hydrogen shares 1 electron with oxygen Since oxygen initially has 6 electrons it has 2 pairs Of electrons that remain unshared

  12. Unshared electron pairs are called LONE PAIRS Shared electron pairs are called SHARED PAIRS or BONDING PAIRS

  13. Nitrogen has a non-bonding pair of electrons But Methane has no non-bonding pairs

  14. Depicting bonds The most common way to depict bonds is not by Lewis dot structures. Instead, a line is drawn for each pair of shared electrons : =

  15. H C H H H How many bonding pairs and Lone pairs are there in CH4 Carbons S and P orbitals Overlap with Hydrogen’s S orbital to form a Hybrid orbital known as a Sigma bond. Its shape is Unique – the tetrahedron CH4 METHANE 4 sigma bonds (4 single covalent bonds)

  16. ** P Cl Cl Cl Lewis dot structure Lone pairs are not Connected to the Parent ion with a line. The electrons are indicated using 2 “dots” Phosphorus’ lone pair How would you draw the Water molecule?

  17. Multiple bonds So far we have looked at atoms sharingone pair of Electrons to form a single covalent bond It is however possible for atoms to share more than a single pair of electrons Oxygen (O2), for example, does this. Let’s see how. Oxygen: 6e-

  18. #1 #2 Multiple bonds Oxygen’s oxidation number is This means it has electrons in it’s valence shell To achieve the octet it needs . -2 6 8 So how does it do this? • A pair of • Electrons from • oxygen #1are shared • 2. Oxygen #2 then • Shares one of its • Pair of electrons to • Complete the octet

  19. H C = O: H H H C = C H H . . . . :O = C = O: The sharing of 2 pairs of electrons is known as a DOUBLE BOND. They can be formed by Molecules having other than just two of the same atoms (like O2 ) Formaldehyde is an example Propene is another. Do the atoms in these molecules have an Octet? Some compounds may even have several double bonds. Carbon Dioxide

  20. Triple Bonds Nitrogen is an example of a compound that is formed By sharing three pairs of electrons. This is called aTRIPLE BOND How many Electrons does Each atom have?

  21. H - C : : : C - H Electrons from carbon 1 Electrons From carbon 2 H - C C - H Triple bonds Another example of a Triple Bond is acetylene Oxy-acetylene torch Acetylene

  22. Bond EnergyThe strength of a Chemical Bond • Energy required to break a chemical bond • Measured in kJ/mole • A large bond dissociation energy corresponds to a strong covalent bond. • Covalent Bond Strength: Triple > Double > Single HBr = 367 kJ/mole

  23. Bond Dissociation Energy The energy necessary to break A bond in a given Compound varies. Different kinds of Bonds take different Energies to break them apart. It would take 436 kJ/mol to break a hydrogen bond. Bond length Bond Strength

  24. Bond Energies

  25. Covalent vs. Ionic Properties

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