CO2 Lewis structure, worked step by step
Carbon dioxide, CO2: a linear, nonpolar molecule. Every step below is worked from the atoms up; the diagram is drawn from coordinates, not copied from anywhere.
1. Count the valence electrons
Carbon is in group 14 and brings 4 valence electrons. Each oxygen is in group 16 and brings 6, and there are 2 oxygen atoms, so the total is 4 + 2 × 6 = 16 valence electrons to place.
2. Draw the structure
Carbon sits in the middle with one double bond to each oxygen. A double bond uses 4 electrons (2 shared pairs), so the 2 double bonds use 8 of the 16 electrons. The remaining 8 electrons sit as 2 lone pairs on each oxygen (4 lone pairs in total, 8 electrons), shown as the dot pairs in the diagram.
Formal charge on carbon: 4 valence electrons − 0 non-bonding − 4 (half of 8 bonding electrons) = 0. Formal charge on each oxygen: 6 valence electrons − 4 non-bonding − 2 (half of 4 bonding electrons) = 0. No charges to mark, which is why none are shown on the diagram.
3. VSEPR shape and bond angle
Carbon has 2 bonding domains (the two double bonds count as one electron domain each) and 0 lone pairs, so it is AX2 in VSEPR terms. With nothing else to push the two domains around, they spread to the maximum possible separation, giving a bond angle of 180° and a linear shape. derived by rule
4. Is it polar?
Each C=O bond is polar on its own: carbon's Pauling electronegativity is 2.55 and oxygen's is 3.44, a difference of 0.89, large enough for the shared electrons to sit closer to oxygen. calculated But the molecule is linear and the two C=O dipoles point in exactly opposite directions, so they cancel. The molecule as a whole is nonpolar: bond polarity is not the same question as molecular polarity, and shape is what settles it here.
5. Molar mass, atom by atom
NIST's standard atomic weight for carbon is the interval [12.0096,12.0116]; this site takes the midpoint of that interval, rounded to three decimal places, as carbon's conventional atomic weight: 12.011. calculated For oxygen, NIST's interval is [15.99903,15.99977], with midpoint (rounded the same way) 15.999. calculated
Adding one carbon and two oxygens: 12.011 + 2 × 15.999 = 44.009 g/mol. calculated PubChem's own computed molecular weight for CO2 is 44.009 g/mol, from its Computed Properties section — the two independent routes, NIST atomic weights summed by hand and PubChem's own computed value, agree.