Chemical bonds.ppt


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Chemical bonds.ppt

  1. 1. Bonding and Molecules
  2. 2. Why atoms form chemical bonds Electrons are in energy levels around the nucleus (electron cloud). The higher the energy level, the more energy is required for an electron to occupy that part of the cloud. The outermost part of the electron cloud contains the valence electrons – that is the valence shell. Maximum number of valence electrons in an atom is 8.
  3. 3.  Atoms are stable when they have 8 valence electrons. When the atoms have 8 electrons, it is called an octet . Atoms must lose, gain or share electrons to attain the octet. Atoms that form bonds with other atoms by sharing them or transferring them is known as the Octet Rule .
  4. 4. There is always an exception!  Hydrogen and Helium  Hydrogen needs only one more to fill its valence shell.  Helium has a full valence shell – it is stable and does not bond with other atoms.
  5. 5. So what about Lithium? Is it easier for Lithium to gain 7electrons or lose 1 electron?
  6. 6. Bond…. Chemical Bonds  Ionic Bonds  They are formed when atoms gain or lose electrons.  If the compound has a metal, then it is an ionic bond.  Ex. xx Na Cl x x x xx
  7. 7.  When it loses 1 Ionization electron to become more stable, it has 11 protons (+) and When atoms gain 10 electrons (-) and or lose an electron, has a +1 charge.  Cl has 17 protons. they become an  When Cl gains 1 ion. electron to complete A Na atom has 11 the octet, it has 17 positively charged protons (+) and 18 protons and 11 electrons (-). negatively charged  It is now an ion with electrons. a –1 charge.
  8. 8. Opposites Attract Since the Na has a + charge and the Cl has a – charge, the two atoms are attracted together and form an ionic bond. They have a 1:1 ratio when they combine…..
  9. 9. Covalent Bonds Atoms that share electrons form covalent bonds. If the atoms have a covalent bond and are the same type of atom…. They are diatomic molecules. Ex. xx xx x x Cl Cl xx x x x x xx
  10. 10. Element Bonding FormulaHydrogen H-H H2Oxygen O-O O2Nitrogen N-N N2Fluorine F-F F2Chlorine Cl-Cl Cl2Bromine Br-Br Br2 Iodine I-I I2
  11. 11. Metallic Bonding Metallic bonds - electrons are distributed equally through a metallic crystal. The electrons in metals can be thought of as being property of all the atoms. The positive nuclei are surrounded by a "sea of electrons" that are all attracted by the nuclei at the same time.
  12. 12. So you ask…. “How do I know if it is covalent or ionic?” Ionic bonds are formed by the attraction of two oppositely charged particles. Covalent bonds are formed when atoms share electrons. Typically bonds between metals and nonmetals form ionic bonds. Bonds between two nonmetals form covalent bonds.
  13. 13. Isn’t it ionic, don’t you think Electron pairs sometimes share unequally in covalent bonds. The attraction an atom has for the shared pair of electrons in a covalent bond is called electronegativity .
  14. 14.  High Electronegativity (need to gain electrons) Low Electronegativity  Atoms in Column 17 (need to lose have high electrons) electronegativity. Atoms in Columns 1 and 2 have low electronegativity. Cl F Br H K Li