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Chemical bonds.ppt

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  • 1. Bonding and Molecules
  • 2. Why atoms form 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. 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. 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. So what about Lithium? Is it easier for Lithium to gain 7 electrons or lose 1 electron?
  • 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 xx x x x
  • 7. Ionization When atoms gain or lose an electron, they become an ion. A Na atom has 11 positively charged protons and 11 negatively charged electrons. When it loses 1 electron to become more stable, it has 11 protons (+) and 10 electrons (-) and has a +1 charge. Cl has 17 protons. When Cl gains 1 electron to complete the octet, it has 17 protons (+) and 18 electrons (-). It is now an ion with a –1 charge.
  • 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. 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 x x xx Cl Cl xx xx x x x x
  • 10. Element Bonding Formula Hydrogen H-H H2 Oxygen O-O O2 Nitrogen N-N N2 Fluorine F-F F2 Chlorine Cl-Cl Cl2 Bromine Br-Br Br2 Iodine I-I I2
  • 11. So you ask…. “How do I know if it is covalent or ionic?”by the Ionic bonds are formed 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.