We gots the #"ozone"#, #O_3#, #"molecule"#...with #3xx6=18*"valence electrons"# to distribute over 3 oxygen centres...
And we would write...#O=stackrel(ddot)O^(+)-O^-#...and from left to write as we face the page, associated with each oxygen atoms there are EIGHT, SEVEN, and NINE electrons associated with each centre. And thus FORMAL CHARGES of #0,+1,-1#...of course the terminal oxygen atoms are equivalent by resonance, and we could write...
#""^(-)O-""^(+)stackrel(ddot)O=O#...
#/_O-O-O=120^@# to a first approx. The actual value is #117^@#, i.e. slightly compressed from the ideal angle of #120^@#, given that the SINGLE oxygen lone pair lies closer to the oxygen atom than the bonding electron pairs, and thus influences molecular geometry.
