how many valence electrons does oxygen have how many valence electrons does carbon have how many valence electrons does nitrogen have how many valence electrons does chlorine have how many valence electrons does hydrogen have how many valence electrons does sulfur have how many valence electrons does boron have how many valence electrons does fluorine have how many valence electrons does bromine have how many valence electrons does calcium have how many valence electrons does iodine have how many valence electrons does aluminum have how many valence electrons does sodium have how many valence electrons does cl have how many valence electrons does helium have how many valence electrons does lithium have how many valence electrons does silicon have how many valence electrons does iron have how many valence electrons does copper have carbon has how many valence electrons oxygen has how many valence electrons