ZnO Structure & Characteristics (15 Important Facts)


ZnO is the chemical formula of zinc oxide and is commonly known as zinc white or calamine. At this junction, we are discussing brief details on ZnO structure.

ZnO can show polymorphism and has three different structures i.e. rocksalt structure, wurtzite structure, and zinc blend structure. The wurtzite structure of ZnO is the most stable structure thermally. ZnO is the metal and non – metal elements combination forming an ionic compound.

ZnO wurtzite shows a hexagonal closed – packed arrangement. The ZnO zinc blend structure can be stable if we grow its cubic substrates. The color of the raw zinc oxide is greyish yellow and in granular form with no smell. We are discussing more briefly valence electrons, shape, bond angle, lone pairs, and various characteristics of ZnO structure with some other facts.

How to draw ZnO structure?

Below we are discussing the details to draw the ZnO Wurtzite structure given below.

Wurtzite structure of ZnO:

  • ZnO structure is composed of Zn2+ and O2- ions.
  • It has a hexagonal closed packing (HCP) arrangement of Zn2+ and O2- ions.
  • It has 6 atoms present per unit cell.
  • In HCP structure it has 6 octahedral voids and 12 tetrahedral voids.
  • The Zn2+ cations cover 75% octahedral sites and ½ tetrahedral sites in a hexagonal closed packing structure.
  • The O2- anions are present at the corners and faces of the hexagon
  • Both the Zn and O atoms have coordination number 4.
  • Each Zn2+ cation is surrounded by 4 O2- anions and each O2- anion surrounds by 4 S2+ cations.
  • It has alternate layers of Zn2+ and O2- ions i.e. O2-, Zn2+, O2-, Zn2+, and so on. Thus it forms an ABAB-type structure.
  • It has 2 asymmetric units in its unit cell of HCP.
ZnO crystal structure

ZnO structure valence electrons

The outermost shell or orbital of an element contains electrons present in it called valence electrons. Take a look at the brief discussion on the ZnO valence electrons.

The ZnO structure contains a total of 8 electrons. Two main elements are involved in the formation of ZnO i.e. zinc and oxygen atoms. The Zn metallic atom presents in the 12th group and contains 2 valence electrons. Similarly, the O non-metallic atoms present in the 16th group have 6 valence electrons in them.

Below are given explanations and steps to calculate the valence electrons of the ZnO structure.

  • The oxygen atom has valence electrons is = 06 x 01 (O) = 06
  • The zinc atom has valence electrons is = 02 x 01 (Zn) = 02
  • The total valence electrons on ZnO structure is = 02 (O) + 06 (Zn) = 08
  • The overall electron pairs present in the ZnO structure are determined by dividing its valence electrons by 2 = 8 / 2 = 4
  • Hence the ZnO structure contains a total of 8 valence electrons and a total of 4 electron pairs.

ZnO structure lone pairs

The unshared or non-bonding electrons of an atom or molecule are called lone pair electrons. Below let us have some discussion on the ZnO lone pair electrons.

The ZnO contains eight lone pairs of electrons. It contains eight valence electrons. There is a loss and gain of 2 electrons between Zn (loss) and O (gain) atoms making ZnO an ionic species. It cannot form a strong covalent bond by electron sharing and has no bond pairs.

The ZnO structure lone pair of electron calculation is explained in the below given following steps.

  • Lone pair electrons on ZnO is = Valence electrons of ZnO  (V. E) – Number of bonds / 2
  • The lone pair electron on Zn atom is = 0 (V. E) – 0 (bonds) / 2 = 0
  • The lone pair electrons on O atom is = 8 (V. E) – 0 (bonds) / 2 = 8
  • Therefore the ZnO structure contains a total of 8 lone pair electrons.

ZnO structure shape

The atomic arrangement of molecules in a definitely closed pack manner forming a shape is known as molecular shape. Take a look below for details on the ZnO shape and geometry.

The ZnO shows linear and tetrahedral shapes.  In accord with the VSEPR theory, ZnO is a diatomic compound composed of only two atoms in it. It has AX generic formula showing the linear geometry and shape of ZnO.

As per the crystallography concept, the ZnO compound shows the sphalerite and wurtzite crystal structures. Thus it shows tetrahedral geometry and shape in its unit cell.

ZnO structure hybridization

The atomic orbitals of atoms or molecules get mixed with each other to produce a new hybrid orbital with similar energy is called hybridization. Take a look at the details of ZnO hybridization.

The ZnO molecule show ‘s’ and ‘sp3’ hybridizations. As the ZnO molecules show two different shapes i.e. linear and tetrahedral. ‘s’ hybridization of ZnO is due to the diatomic nature having two atoms attached beside each other. ‘sp3’ hybridization of ZnO is due to its coordination number 4.

Each Zn2+ ion surrounds with 4 O2- and each O2- surrounds with 4 Zn2+ ions at the corners of a regular tetrahedron. The Zn and O atomic orbitals get overlap and mixed with each other and produce a new ‘sp3’ hybrid orbital s of equivalent energy.

ZnO structure angle

The alternate bonds behind the central atom form an angle or gap which is known as the bond angle. Let us see the brief detailed description of the ZnO molecule bond angle.

The ZnO has 180 – degree and 109.5 – degree bond angles. The 180 – degree bond angle is present in the linear geometry of the ZnO crystal structure, while the 109.5 – degree bond angle is present in the tetrahedral geometry of the ZnO crystal structure.

Is ZnO solid or gas?

The compounds which have closed – packed arrangements of atoms and are hard in nature are called solid compounds. Let us see whether ZnO is a solid or a gaseous compound.

ZnO is a solid compound. The Zn2+ and O2- ions get closely packed with each other with a slight covalent bond due to the overlapping of atomic orbitals of Zn and O atoms. It also forms a crystal structure as wurtzite structure and is available in solid greyish yellow or white granular form powder.

Is ZnO soluble in water?

The dependency of solute to get dissolved in water solution at its maximum amount is called the solubility of water.

ZnO compound is insoluble in water. If we add ZnO to water it forms a turbid solution and finally settles down at the bottom. ZnO has more lattice energy than its hydration energy. Thus the bonds between ZnO compounds cannot detach to form a hydrogen bond with water molecules and remain insoluble.

Is ZnO polar or nonpolar?

The electron distribution and the symmetry of atoms and the opposite charge on it determine the polar or non-polar molecule. Let us see if ZnO is polar or non-polar.

The ZnO compound is polar in nature. It has the electronegativity difference value of 1.79 between Zn and O atoms. This shows that ZnO is a highly polar compound. It shows no equivalent electron distribution on both Zn and O atoms due to that it has an asymmetrical shape and geometry.

All the electron density attracts toward more electronegative O atom. Thus, generates the net dipoles on it forming two opposite charges i.e. partial positive charge on Zn atoms and partial negative charge on O atoms confirming it is a polar molecule.

Is ZnO molecular compound?

The compounds containing sigma covalent strong bonds with the presence of different small molecules are called molecular compounds. Let us see whether ZnO is molecular or not.

ZnO is not a molecular compound. It is an ionic compound. It cannot contain any strong sigma covalent bond because it has a strong ionic bond due to the exchange of electrons with each other. Also, its molecular formula does not show the presence of small other molecules in it.

Is ZnO acid or base?

The proton acceptor shows basic nature and the proton donor shows acidic nature of compounds. Below we have a brief discussion on whether ZnO is acid or a base in nature.

ZnO does not show acidic or basic nature. It is a naturally occurring salt. It is a metal oxide that comes under amphoteric oxides and reacts both with acid and base compounds like hydrochloric acid (HCl) and sodium hydroxide (NaOH). The reactions of ZnO with HCl acid and NaOH base are given below.

ZnO (s) + 2 HCl (aq) → ZnCl2 (s) + H2O (l) (basic reaction of ZnO)

ZnO (s) + 2 NaOH (aq) → Na2ZnO2 (s) + H2O (l) (acidic reaction of ZnO)

Is ZnO electrolyte?

The compound that gets ionized by adding to water to conduct electricity is called electrolytes.  Take a brief detailed look at ZnO electrolytic nature given below.

ZnO is an electrolytic compound. As it is an ionic compound. It cannot readily ionize into the water there is a need for external energy like heat to dissolve it in water. On ionization, it can act as an electrolyte and can conduct electricity on the application of external current.

Is ZnO salt?

Salts are solid crystalline compounds that get formed due to acid – base reactions in the form of a precipitate. Let us see below in detail whether the ZnO compound is a salt or not.

ZnO is a compound present in salt form. It is a combination of metal and non-metal. When metal and non-metal elements get to react with each other they form salt as a product. It occurs naturally in the form of zincite. The reaction for zinc oxide formation is shown below.

Zn + O → ZnO

Zn2+ + O2- → ZnO

Zn(OH)2 → ZnO + H2O

Is ZnO ionic or covalent?

The electrostatic force of attraction within atoms shows ionic compounds and sigma covalent bonds within atoms show covalent compounds. Let us see whether ZnO is ionic or covalent.

ZnO is an ionic compound.  The Zn atom donated 2 valence electrons to the O atom forming a +2 charge on it. The O atom gains 2 valence electrons from the Zn atom forming a -2 charge. It forms a strong ionic bond within Zn and O atoms due to the electrostatic force of attraction and not by a covalent bond.

Is ZnO amphoteric?

The compounds which can react with both acidic and basic compounds are called amphoteric compounds. Below we are discussing on the ZnO compound is amphoteric or not.

ZnO has amphoteric nature. The elements belonging to the 2nd, 13th, 14th, and 15th periodic table groups can form amphoteric oxide. The Zn metal belongs to the 2nd group and reacting with O atoms forms amphoteric oxide. Thus it can react with a strong acid like (H2SO4) and strong bases like (KOH).

The reaction of ZnO with sulphuric acid (H2SO4) and potassium hydroxide (KOH) is given below.

ZnO + H2SO4 → ZnSO4 + H2O

ZnO + 2 KOH → K2ZnO2 + H2O

Is ZnO semiconductor?

Semiconductors are the compounds that have the values between conductors i.e. metals and insulators i.e. non-metals. Take a look at the details on whether ZnO is a semiconductor or not.

ZnO is a semiconductor. It acts as an n-type semiconductor due to the impurities like P, As, etc. present in the holes or vacant places of O atom in the crystal structure called intrinsic defect. It has a wide band gap value of 3.3 eV.

It has free electrons due to impurities and free electrons are charge carriers to conduct electricity.

Conclusion:

ZnO shows Wurtzite crystal structure in its stable form. It has 8 valence electrons and lone pair electrons. It shows linear and tetrahedral shapes with ‘s’ and ‘sp3’ hybridization having 180 and 109.5 degree bond angles. It is solid ionic water insoluble electrolytic salt. It has amphoteric nature to react with acid and base both. It can act as an n-type semiconductor.

Dr. Shruti Ramteke

Hello everyone I am Dr. Shruti M Ramteke, i did my Ph.D in chemistry. I have five years of teaching experience for 11-12 standard, B,Sc and MSc in chemistry subject. I have published total five research articles during Ph.D on my research work and i have fellowship from UGC for my Ph.D. My Masters with specilization Inorganic chemistry and my graduation with chemistry, zoology and environmental science subjects. thank You

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