A water molecule is composed of one oxygen and two hydrogen atoms. Many of us want to know if water molecule is covalent or ionic. So, I come up with this article to let you know the detailed information about it. So, is H2o (water) an ionic or a covalent compound? Yes, H2O (water) is a covalent compound because of the low difference in the electronegativity of Hydrogen (2.2) and Oxygen (3.44) atoms due to which the hydrogen and oxygen atoms share electrons with each other forming polar covalent bonds. Sharing of electrons between oxygen and hydrogen atoms, by the formation of a covalent bond, results in the formation of a covalent compound. The next question you may ask here is “Why is water covalent?”
Why is H2O (Water) Covalent?
Well, one simple reason is both oxygen and hydrogen are non-metals and it is a well-known fact that non-metals form a covalent bond with each other. The oxygen atom has six electrons in its valence shell and requires two electrons to complete its octet while both hydrogen atoms require one electron each to gain stability. You must also check out the article on the lewis structure of H2O after completing this article. In addition, the electronegativity difference between the two atoms required for the formation of a covalent bond should be less than 1.6 (few books mention it to be less than 2). In the case of water the electronegativity value for the Oxygen atom is 3.44 and for the Hydrogen atom is 2.1, creating an electronegativity difference of 1.34 making the bond between these two atoms covalent. However, in the case of the water molecules, the covalent bond is formed through unequal sharing of electrons between oxygen and hydrogen atoms. The oxygen being more negative than hydrogen pulls the shared pair of electrons slightly towards itself, giving the oxygen atom a slightly negative and hydrogen atom a slight positive charge, and therefore, water is known to be a polar covalent molecule. We will talk about the polarity of the water molecules in the coming sections.
Why do Atoms form Bonds?
You would understand the above-mentioned concept better if you know the reason for chemical bonding between various atoms. As per the octet rule the atoms have a tendency to stabilize their valence shell by completing their octet i.e. acquire eight electrons in their outermost shell. The exceptions to the octet rule are hydrogen and helium atom. Hydrogen, which is a group first element, has one electron in its outermost shell and is completely satisfied when provided with two valence electrons. This stability of hydrogen is derived from the electronic configuration of its nearest noble gas helium which is stable with two valence electrons. To complete their octet the atoms may lose, gain, or share their valence electrons owing to which they form ionic or covalent bonds amongst themselves. This maximizes the stability of an atom.
What are Ionic or Covalent Compounds?
As the name indicates ionic compounds are formed owing to ionic bonds. These are the electrostatic forces that exist between the two oppositely charged ions viz anion (positive) and cation (negative). The ions can be monoatomic, for example, Na+, K+, Cl-, etc., or polyatomic such as HSO4-, NH4+, etc. based on the number of atoms involved. Ionic bonds are mostly formed between a metal and a non-metal.
The major reason for the formation of ionic bonding is the difference in electronegativity of combining atoms. When the electronegativity difference is more than 1.6, it results in the formation of ionic bonds. The more electronegative atom pulls the electron pair towards itself at the time of chemical bond formation due to which it acquires a negative charge and the other atom donating the electron acquires a positive charge. Usually, the net charge on such compounds is zero, as the positive and negative are nullified with each other and therefore, such compounds are electrically neutral. One interesting ionic compound is CaF2. Go through the article on is CaF2 ionic or covalent. The covalent bond on the other hand is formed due to the sharing of valence electrons between two bonding atoms. Such bonds exist between the atoms with comparable electronegativity (less than 1.6), mostly two non-metals. Covalent compounds are electrically neutral and owing to the absence of ions are poor conductors of electricity. Unlike ionic compounds, they have low melting and boiling point and usually occur as gases or liquids at room temperature. Covalent bonds can further be distinguished as a polar and non-polar covalent bonds.
Polar Covalent Bond vs Non-Polar Covalent Bond
In the case of non-polar covalent bonds the electrons are equally shared between the two atoms i.e. they spend equal time around each nucleus and the probability of these electrons being near to each atom is equal. Such bonds exist between identical atoms such as H2, Cl2, etc. Here, the electronegativity difference is less than 0.4. Check out the article on the polarity of H2. On the other hand, when a covalent bond is formed between dissimilar atoms the shared electrons are not equally distributed between the two atoms resulting in the development of a slight positive and slight negative charge on the atom from which electrons are pulled away and the one that pulls electrons towards itself, respectively. This occurs due to the electronegativity difference between the two atoms which should lie somewhere between 0.4 – 1.6. Like in the case of H2O, the oxygen atom is more electronegative due to which the probability of finding the shared pair of electrons near the oxygen atom is higher owing to this oxygen develops a slightly negative charge and hydrogen a slight positive charge. These partial charges are represented with greek letter delta ‘δ’ and are written as δ+ and δ-.
The Polarity of H2O (Water) Molecule
As discussed earlier the bond between hydrogen and oxygen atoms inside a water molecule is a polar covalent bond. The polarity of H2O is due to its bent shape which arises to compensate for the attraction and repulsion forces existing between the two atoms. The more electronegative oxygen atom pulls the electrons towards itself due to which a negative charge develops around this atom and hydrogen atoms become slightly positive. As a result the two positively hydrogen atoms are equally attracted towards the negatively charged oxygen atom but remain as far as possible from each other owing to similar charges. Also, the lone pair of electrons present on the oxygen tend to repel each other pushing the hydrogen atoms away from the oxygen atom. This results in distortion of linear geometry and an angle of 104.3° is formed. BTW, I have also written a specific article on this topic. Have a look at the polarity of water.
Electronegativity
The tendency of an atom to attract the electron towards itself is known as electronegativity. It plays a decisive role in chemical bonding and is based on the electronegativity difference between the two atoms. it can be determined whether the bond between them will be covalent or ionic in nature. The electronegativity of any substance is measured using the Pauling scale. This can be deduced from the table given below: In the periodic table, electronegativity increases towards the top of a column and decreases from right to left in a row.
Properties of Water
Water is an amphoteric substance i.e. it can behave as both acid (proton donor) and base (proton acceptor). It has a pH value of 7 i.e. it is a neutral substance. It is referred to as a universal solvent as it can dissolve the maximum number of substances in comparison to any other solvent. A few important properties of water are given in the table below:
Hydrogen Bond
These are the special type of intermolecular forces that exist between a hydrogen atom and an electronegative atom due to dipole-dipole interaction between them. In the case of water, the hydrogen atoms of one water molecule are bonded to the oxygen atom of another molecule owing to hydrogen bonding. These forces are quite weak in comparison to actual chemical bonds i.e. ionic or covalent bonds but are strong in comparison to dispersion forces or dipole-dipole interaction. These play a very important role in determining the various properties of water such as shape, solubility, etc. The high melting and boiling point of water is due to hydrogen bonding.
Uses of Water
Water forms almost 60 percent of our body weight and is an indispensable part of our body, functions. Inside our body, it is required to • Help maintain temperature, through sweating • To aid in the digestion process • To carry out cognitive functions (dehydration can adversely affect the brain functioning) • For excretion (through perspiration, urination, etc.) • Helps boost metabolism increasing the physical strength of a person Other than the human body water also forms an extremely important part of the environment required by most living organisms to carry out their life functions. It is also required by humans for agriculture, in various industries, recreational activities, etc.
Conclusion
Water is a polar covalent molecule in which the oxygen and hydrogen atoms carry slight negative and slight positive charges, respectively. The covalent character of water is due to the small electronegativity difference between hydrogen and oxygen atom. The polarity of water is due to its bent shape which arises from various intra-molecular forces. Other than covalent bonding another type of chemical interaction known as hydrogen bonding also occurs between different molecules of water.
