HCO2- Lewis Structure, Characteristics:29 Complete Quick Facts

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HCO2–or formate ion is a derivative and salt of the formic acid. Let us discuss some important facts about the structure of HCO2– in detail.

The basic structure of HCO2– contains one atom each of hydrogen, carbon and 2 atoms of oxygen. The IUPAC name of this structure is methanoate.  It has been observed that there is quite high plasticity in HCO2– molecule which allows it to adopt various structures.

The observed molecular weight of formate ion is about 45.01 g/mol. When formic acid loses one of its proton, it gives rise to formate ion. In the below sections we are going to have a closer approach towards various properties like lewis structure, resonance, acidity, etc.

How to draw HCO2– lewis structure?

By using lewis structure concept it becomes easier to understand the type of bonding. Let’s understand the method of drawing lewis structure for HCO2– .

1.Finding the total number of valence electrons

The lewis structure of HCO2– has 18 valence electrons. Hydrogen contributes one electron, carbon has 4 and oxygen contributes 12 electrons (6 electrons each by 2 oxygen atoms). One extra valence electron due to the -1 charge.

2. Deciding the atom with least electronegativity

In this step, the atom which has to be placed at the centre is decided. So the atom that has the least electronegativity will be placed in the middle of the structure. Electronegativity of carbon among the rest of the atoms is less. Hence carbon is placed at centre of the structure.

3. Arranging the electrons pair between the atoms

Carbon shares one pair of electrons with hydrogen forming a single bond. As we can see there are 2 oxygen atoms in the structure. So carbon shares one electron pair with one carbon and two electron pairs with the other carbon atom. One electron is shown outside the structure as the minus sign.

HCO2–lewis structure resonance

Resonance is the delocalization of electrons. Let us discuss the HCO2– lewis structure resonance concept.

Resonance is possible in HCO2– as oxygen contains lone pairs of electrons, which has the capability to delocalize. Hence there are 2 resonance structures that are possible for the HCO2– molecule. This resonance structures help us in predicting the more accurate structure for the molecule.

FORM
Resonating structures of formate ion

HCO2– lewis structure shape

The type of atoms have a great impact on the shape of the molecule. Let us discuss this in detail.

The shape of HCO2– is trigonal planar. We can see that the central atom is bonded to 3 atoms. And in a trigonal planar type of geometry similar pattern is observed. The atoms in this kind of arrangement are also referred to as peripheral.

HCO2– lewis structure formal charge

Formal charge is the charge that resides on atoms and is useful in predicting lower energy. Let us discuss the formal charge on HCO2–.

The formal charge of HCO2– lewis structure is negative one (-1). And this resides on the second oxygen of the structure.

The equation for the calculation of formal charge is

  • Formal charge = valence electrons –  lone pair of electrons – No. of bonds
  • Formal charge on hydrogen = 1 – 0 – 2/2 = 0
  • Formal charge on carbon = 4 – 0 – 8/2 = 0
  • Formal charge on first oxygen = 6 – 4 – 4/2 = 0
  • Formal charge on second oxygen = 6- 6 – 2/2 = -1

Hence the formal charge according to above calculation on HCO2– is -1.

HCO2– lewis structure angle

In the section of structure we have discussed that HCO2– is trigonal planar. Let us analyze the bond angle in HCO2– .

The bond angle in HCO2– is 120°. It has been observed that the hybridization of carbon (the central atom) is sp2 and its steric number is 3. Also there is no lone pair on the central carbon atom.

HCO2– lewis structure octet rule

Octet rule is the term used to describe bonding ability of atoms, meaning atoms prefer eight electrons in the outer shell. Let us see in HCO2–.

HCO2– satisfies the octet rule. The central carbon atom forms one single bond with one oxygen and hydrogen each (sigma bond). Forms double bond with the other oxygen atom by sharing two pairs of electrons.

HCO2– lewis structure lone pairs

Lone pairs in a molecule are the electrons that are not involved in the covalent bonding of the molecule. Let us see for HCO2–.

There are 5 lone pairs of electrons in the molecule. One oxygen of the structure has 3 lone pairs of electrons (oxygen bonded to the central atom with a single bond). The other oxygen has 2 lone pairs of electrons (oxygen bonded with a double bond to the central atom).

HCO2– valence electrons

The term is used to refer to the electrons that are present in the outermost shell of an atom. Let us discuss for HCO2–.

The total valence electrons that are present in the HCO2– lewis structure are 18. One electron contributed by the hydrogen atom. Four electrons are contributed by the central carbon atom and 6 valence electrons each by 2 oxygen atoms. One electron due to the charge on the structure.

HCO2– hybridization

The intermixing of orbitals to give new set of hybrid orbitals is called hybridization. Let us analyze for HCO2–.

The hybridization of the central atom carbon is sp2. The oxygen bonding to the central atom with sigma bond has sp3 hybridization. The oxygen bonding to the central atom with pie bond has sp2 hybridization.

HCO2– solubility

Solubility refers to the degree to which a substance can dissolve in a given solvent. Let us discuss for HCO2–.

List of compounds in which HCO2– is soluble:

  • Water 97.2 g/100 mL at 20°C
  • Ethanol
  • Formic acid
  • Glycerol

Is HCO2– soluble in water?

Most of the compounds are soluble in water but at varying temperature ranges. Let us see for HCO2–

HCO2– is soluble in water. The solubility differs at different temperatures. 43 g/100mL at zero °C and 160 g/100mL at 100°C. Water being a universal solvent has the capability to dissolve almost all the compounds. We can see that as the temperature increases solubility of formate ion also increases.

Is HCO2– an electrolyte?

A substance that has the potential to break in the form of ions and conduct electricity are known as electrolytes. Let us see if HCO2– is an electrolyte.

HCO2– is an electrolyte. When the formate ion comes in contact with aqueous medium, it has the capacity to dissociate into ion. This ions in turn can conduct electricity.

Is HCO2– a strong electrolyte?

A strong electrolyte is a substance whose ions are capable to dissociate completely into the ionic form. Let us see how strong electrolyte is HCO2–.

HCO2– is considered to be a comparatively weak electrolyte. The reason is its Ka value is around 1.8.( Ka is the dissociation constant which helps us in understanding the extent of dissociation )1.8 is quite a low value.

Is HCO2– acidic or basic ?

A acid has the capability to dissociate almost completely in comparison to base. Let us see if HCO2– is acidic or basic.

HCO2– is the anion of an acid. Formate ion is a derivative of formic acid ( a weak acid ). As we can see the dissociation constant value for HCO2– is 1.8, which is usually observed in weak acids. HCO2– is an acid but a weak acid. The reason for this is that it is the monocarboxylic anion acid of a weak acid .

Is HCO2– a strong acid?

A strong acid has the ability to dissociate quickly and almost completely into ions. Let us see how strong is formate ion.

HCO2– is a weak acid. The reason for its weak acidic behavior is that it does not have the capability to dissociate completely under aqueous conditions.

Is HCO2– polyprotic acid?

 A polyprotic acid is an acid which can give away many protons when under aqueous conditions. Let us analyze for HCO2–.

HCO2– is not a polyprotic acid. The reason is that it cannot give away many protons in aqueous solution, as it only has one proton in the structure. HCO2– is not a polyprotic acid as it is formed when formic acid loses one of its proton. Meaning there is already lack of protons.

Is HCO2– a lewis acid?

A lewis acid is the one which can  accept a proton. Let us see for HCO2–.

HCO2– is a lewis acid. The lewis structure itself indicates this, there is one extra electron in the structure ( the minus sign). So it can accept one proton and complete its structure.

Is HCO2– an Arrhenius acid ?

Arrhenius acid is a substance that increases the concentration of H+ ions in the solution by releasing protons. Let us see for HCO2–.

HCO2– is an Arrhenius acid but not a very strong one. The reason is it has only one proton, that also is not released very easily. Hence on dissolving formate ion in a solution it will not much increase the concentration of H+ ions in the solution.

Is HCO2– polar or nonpolar?

A polar substance has a considerable amount of charge separation and non polar substance will not have charge separation. Let us see for HCO2–.

HCO2– is a polar molecule has the charges on the molecule are seen to be not evenly distributed. Meaning there is considerable amount of charge separation in the molecule.

Why and how HCO2– is polar ?

HCO2– is polar because the values of electronegativity for oxygen, carbon and hydrogen are 3.5, 2.2 and 2.5 respectively. When we subtract the electronegativity values for bonds we will observe there is some difference in the values. Consider the C-H bond the electronegativity difference is 0.3 and for C-O is 1.0.

Is HCO2– linear ?

A linear molecular has a very simple geometry with a bond angle of 180 °. Let us see if HCO2– is linear or not.

HCO2– is not linear. Already discussed in the above sections that formate ion has a trigonal planar geometry and 5 lone pairs of electrons. Hence it is not possible for the molecule to adapt a linear shape.

Is HCO2– paramagnetic or diamagnetic?

Substance containing unpaired electrons are referred to as paramagnetic and the ones with no unpaired electrons are diamagnetic. Let us analyze for HCO2–.

HCO2– is paramagnetic. The reason is there is one electron in the structure which remains unpaired ( which is written as the minus sign on the structure).

HCO2– boiling point

Boiling point for a substance is referred to the temperature where pressure of vapour and atmosphere equalize. Let us find for HCO2–.

The boiling point of HCO2–  is around 105-109 °C under normal atmospheric conditions (760 mmHg). It may vary with change in atmospheric conditions.

Is HCO2– ionic or covalent?

A covalent bond is formed as a result of sharing of electrons between atoms and ionic is formed due electrostatic attraction. Let us see for HCO2–.

HCO2– is covalent. The reason is in the above section we have seen the bond formation in the molecule occurs as a result of electron sharing.

Hydrogen bonding in HCO2–

Hydrogen bond results when a proton bonds with a electronegative atom. Let us see if it exits in HCO2–.

Hydrogen bonding is observed in HCO2–. There is hydrogen which has the capability to bond in intermolecular manner with the electronegative atom oxygen present in the structure.

Is HCO2– dipole?

A dipole arises when there is charge separation in the molecule. Let us analyze for HCO2–.

HCO2– has a dipole as there exists charge separation. The observed dipole moment is around 1.33 Debye.

Is HCO2– monoprotic, diprotic or triprotic ?

Substance with one proton in the structure is called monoprotic, diuretic has 2 and triprotic has 3. Let us see for HCO2–.

Formate ion is monoprotic. There exists only one proton in the structure of the molecule.

Conclusion

HCO2– is a derivative of formic acid. The type of bonding is covalent with 5 lone pairs of electrons. The observed geometry is trigonal planar with a bond angle of 120°C.

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