Water is written H₂O. With school atomic masses the molar mass is 18 g/mol. Water is a polar molecule with two O-H bonds and a bent geometry.
H₂O
WaterNH₃
AmmoniaCO₂
Carbon DioxideH₂O₂
Hydrogen PeroxideSO₂
Sulfur DioxideNO₂
Nitrogen DioxideHCl
Hydrochloric AcidH₂SO₄
Sulfuric AcidHNO₃
Nitric AcidCH₄
MethaneC₂H₆
EthaneC₃H₈
PropaneC₄H₁₀
ButaneC₂H₄
EthyleneC₂H₂
AcetyleneC₆H₆
BenzeneC₇H₈
TolueneC₁₀H₈
NaphthaleneC₆H₁₂
CyclohexaneCH₃OH
MethanolC₂H₅OH
EthanolCH₃COOH
Acetic AcidHCHO
FormaldehydeCH₃COCH₃
AcetoneC₄H₁₀O
Diethyl EtherC₂H₇N
EthylamineC₂H₅NO
AcetamideC₆H₁₂O₆
GlucoseC₆H₁₂O₆
FructoseC₁₂H₂₂O₁₁
SucroseCO(NH₂)₂
UreaC₂₇H₄₆O
CholesterolC₉H₈O₄
AspirinC₈H₉NO₂
AcetaminophenC₁₃H₁₈O₂
IbuprofenC₈H₁₀N₄O₂
CaffeineC₆H₆N₂O
NicotinamideC₆H₈O₆
Ascorbic AcidC₁₆H₁₈N₂O₄S
Penicillin GC₂H₆O₂
Ethylene GlycolC₈H₈
StyreneC₂H₃Cl
Vinyl ChlorideC₃H₅NO
AcrylamideC₆H₁₁NO
CaprolactamLiCl
Lithium chlorideNa₂O
Sodium oxideNaCl
Sodium chlorideMgF₂
Magnesium fluorideAlCl₃
Aluminum chlorideCaO
Calcium oxideCaC₂
Calcium carbideKNO₃
Potassium nitrateMg₃(PO₄)₂
Magnesium phosphateAl₂(SO₄)₃
Aluminum sulfateMg(OH)₂
Magnesium hydroxideNH₄Cl
Ammonium chlorideNH₄OH
Ammonium hydroxideCuO
Copper(II) oxideCu₂O
Copper(I) oxideFeSO₄
Iron(II) sulfateFe₂(SO₄)₃
Iron(III) sulfatePbCO₃
Lead(II) carbonateMgO
Magnesium oxideAl₂S₃
Aluminum sulfideLiF
Lithium fluoride(NH₄)₂S
Ammonium sulfideKF
Potassium fluorideNiCl₂
Nickel(II) chlorideKCN
Potassium cyanideCH₃COONa
Sodium acetateCaCO₃
Calcium carbonateNa₃P
Sodium phosphideBeBr₂
Beryllium bromideFeO
Iron(II) oxideHg₂Cl₂
Mercury(I) chlorideHg(NO₃)₂
Mercury(II) nitrateCH₃COOCu
Copper(I) acetateSiO₂
Silicon dioxideP₄O₁₀
Tetraphosphorus decaoxideN₂O₅
Dinitrogen pentoxideCO
Carbon monoxideHF
Hydrogen fluoridePCl₅
Phosphorus pentachlorideCF₄
Carbon tetrafluorideSF₆
Sulfur hexafluorideNBr₃
Nitrogen tribromideN₂O
Dinitrogen monoxideN₂O₃
Dinitrogen trioxideCS₂
Carbon disulfideCl₂O₇
Dichlorine heptoxideBF₃
Boron trifluorideCCl₄
Carbon tetrachlorideSO₃
Sulfur trioxideSiCl₄
Silicon tetrachlorideP₂S₅
Diphosphorus pentasulfideBCl₃
Boron trichloridePBr₃
Phosphorus tribromideCBr₄
Carbon tetrabromideNF₃
Nitrogen trifluorideOF₂
Oxygen difluorideNCl₃
Nitrogen trichlorideH₂S
Hydrogen sulfidePH₃
PhosphineBeCl₂
Beryllium chlorideHCN
Hydrogen cyanideClF₃
Chlorine trifluorideXeF₂
Xenon difluorideTetrahedral
Bent
Water is a polar molecule with two O-H bonds and a bent geometry. Its hydrogen bonding gives it unusual properties such as high boiling point and strong solvent power.
Properties
Molar mass
18.015 g/mol
Boiling point
100 °C
Melting point
0 °C
Density (20°C)
0.998 g/cm³
Hybridization (O)
sp³
Uses
Universal solvent in chemistry · Cooling and heat transfer · Drinking water and sanitation · Biochemical reactions in cells
Fun Fact
Ice is less dense than liquid water, so lakes freeze from the top and aquatic life can survive below.
Exam note
Systematic name
Water
Compound class
It is a polar covalent molecule with a bent shape.
Formula unit
Two hydrogen atoms bond covalently to one oxygen atom. Oxygen keeps two lone pairs.
Aqueous solution
Pure water is treated as neutral at 25 °C, with a pH of 7.
Watch the formula
With school atomic masses the molar mass is 18 g/mol: 2×1 (H) + 16 (O). The bond angle is about 104.5 degrees. Ice is less dense than liquid water, so lakes freeze from the top.
Molar mass calculation
Masses given in the question come first. When none are given, school values put the total at 18 g/mol.
+
= 18 g/mol
H₂O
The same count with periodic-table atomic masses gives 18.015 g/mol.
| Element | Atom count | Contribution (g/mol) | Mass % |
|---|---|---|---|
| Hydrogen (H) | 2 | 2.016 | 11.2 |
| Oxygen (O) | 1 | 15.999 | 88.8 |
| Total | 18.015 | 100 |
Common questions
What is water?
Water is a polar molecule with two O-H bonds and a bent geometry. Its hydrogen bonding gives it unusual properties such as high boiling point and strong solvent power.
What is the formula of water?
Water is written H₂O. The systematic name is Water. Two hydrogen atoms bond covalently to one oxygen atom. Oxygen keeps two lone pairs.
What is the molar mass of water?
Water has a molar mass of 18.015 g/mol from the atomic masses on the periodic table. With school atomic masses the total is 18 g/mol, counting 2 hydrogen and 1 oxygen.
Is water an acid or a base?
Pure water is treated as neutral at 25 °C, with a pH of 7.
What is water used for?
Water is used for universal solvent in chemistry, cooling and heat transfer, drinking water and sanitation and biochemical reactions in cells.
What should you watch for with water on an exam?
With school atomic masses the molar mass is 18 g/mol: 2×1 (H) + 16 (O). The bond angle is about 104.5 degrees. Ice is less dense than liquid water, so lakes freeze from the top.