AP Chapter 8 - 1 Chapter 8 Bonding What is a Bond? c A...

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Unformatted text preview: 1 Chapter 8 Bonding What is a Bond? c A force that holds atoms together. c Why? c We will look at it in terms of energy. c Bond energy- the energy required to break a bond. c Why are compounds formed? c Because it gives the system the lowest energy. Ionic Bonding c An atom with a low ionization energy reacts with an atom with high electron affinity. c A metal and a non metal c The electron moves. c Opposite charges hold the atoms together. Coulomb's Law c E= 2.31 x 10-19 J nm(Q 1 Q 2 )/r c Q is the charge. c r is the distance between the centers. c If charges are opposite, E is negative c exothermic c Same charge, positive E, requires energy to bring them together. What about covalent compounds? c The electrons in each atom are attracted to the nucleus of the other. c The electrons repel each other, c The nuclei repel each other. c The reach a distance with the lowest possible energy. c The distance between is the bond length. Energy Internuclear Distance 2 Energy Internuclear Distance Energy Internuclear Distance Energy Internuclear Distance Energy Internuclear Distance Bond Length Energy Internuclear Distance Bond Energy Covalent Bonding c Electrons are shared by atoms. c These are two extremes. c In between are polar covalent bonds. c The electrons are not shared evenly. c One end is slightly positive, the other negative. c Indicated using small delta . 3 H - F + - H - F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - H - F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - +- Electronegativity c The ability of an electron to attract shared electrons to itself. c Pauling method c Imaginary molecule HX c Expected H-X energy = H-H energy + X-X energy 2 c = (H-X) actual- (H-X) expected Electronegativity c is known for almost every element c Gives us relative electronegativities of all elements. c Tends to increase left to right. c decreases as you go down a group. c Most noble gases arent discussed. c Difference in electronegativity between atoms tells us how polar the bond is. Electronegativity difference Bond Type Zero Intermediate Large Covalent Polar Covalent Ionic Covalent Character decreases Ionic Character increases 4 Dipole Moments c A molecule with a center of negative charge and a center of positive charge is dipolar (two poles), c or has a dipole moment. c Center of charge doesnt have to be on an atom. c Will line up in the presence of an electric field. H - F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - H- F + - +- How It is drawn H - F + - Which Molecules Have Dipoles?...
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AP Chapter 8 - 1 Chapter 8 Bonding What is a Bond? c A...

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