CaS Lewis Structure & Characteristics: 15 Complete Facts

CaS or calcium sulfide is a white crystalline chemical compound having molecular weight 72.143 g/mol. Let us discuss the structure and characteristics of CaS in detail.

Calcium sulfide is crystalized in cubic structure like rock salt. It is a highly ionic compound with hygroscopic nature.  It is insoluble in ethanol or methanol but reacts with water in aqueous solution. It possesses high density (2.59 g/cm3) due to its crystal structure.

Let us explore the lewis structure, hybridization, solubility, lone pair, valence electrons, solubility of CaS with detailed explanations.

How to draw CaS lewis structure?

Lewis structure shows the nonbonding electrons as the electron dot around the respective atoms in the molecule. Let us talk about this.

CaS lewis structure consists of two oppositely charged divalent ions, calcium and sulfide ion. Calcium becomes Ca2+ and sulfur becomes S2- in calcium sulfide. Calcium donates its two valence electrons from its 4s orbital and sulfur accepts these two electrons in its 3p orbital.

After donating and accepting of two electrons, a strong ionic interaction is generated between these two ions which is defined as ionic bond.

cas lewis structure
CaS Lewis Structure

CaS Lewis Structure Resonance

Resonance is defined as the delocalization of electron cloud due to overlapping of pi orbitals. Let us explain it in brief.

Lewis resonance structures of CaS are not possible as the constituent atoms are not connected through covalent bonds with each other. In ionic compounds electron cannot be delocalized. It is completely transferred from less electronegative to more electronegative atom.

Electrons are delocalized through pi bonds in covalent bonded molecule and Lone pairs are participating in resonance. Therefore, ionic compounds have no contribution in resonance as they have no lone pairs.

CaS Lewis Structure Shape

Lewis structure shape gives a clear idea about the three-dimensional arrangement of the atoms in a molecule. Let us give an overview on it.

The lewis structure shape of CaS is cube like crystalline structure. In this crystal of CaS, each S2- ion is surrounded by an octahedron of six positively charged Ca2+ ion and each of the Ca2+ is surrounded by the octahedron containing of six S2- ion.

Due to having close packed cube like structure, the density as well as melting and boiling point of CaS is very high. Huge amount of energy is required to break this crystal-like structure.

CaS Lewis Structure Formal Charge

Formal charge, known as fake charge, is defined as the charge carried by the individual atom in a molecule. Let us explain it in detail.

Calculation of the lewis structure formal charge of CaS is not possible as it is an ionic compound. It contains two ionis which carry net charge +2 and -2, not formal charge.

Formal charge is calculated using this formula = {Total number of valance electrons – number of electrons remain as nonbonded – (number of electrons involved in bond formation/2)}. In CaS, there is no existence of nonbonding as well as bonding electrons. Therefore, we cannot calculate formal charge for CaS.

CaS Lewis Structure Angle

Angle or bond angle is determined between two covalent bonds and one atom in a covalent molecule. Let us discuss it.

The lewis structure angle of CaS is not determined because it is not a covalent compound. There is no covalent bond in CaS as Ca2+ and S2- are attached with each other through strong inter ionic attraction which is the key property of any ionic compound.

Determination of bond angle is one of the most important works to decide its structure as well as the hybridization of the central atom.

CaS Lewis Structure Octet Rule

Octet rule is a rule of chemistry which states that any atom should contain eight electrons in its valence shell like its nearest noble gas. Let us talk about this.

The lewis structure of CaS obeys octet rule as the constituent atoms of it entirely satisfies the octet rule. After being Ca2+ from Ca, it achieves eight electrons in its 3s and 3p orbital. After accepting two electrons from calcium sulfur also attains octet rule like its nearest noble gas argon.

Calcium and sulfur, both of the atoms in CaS achieves 3s2 3p6 electron configuration like their nearest noble gas of periodic table, argon. Therefore, octet rule is satisfied in case of Calcium sulfide.

CaS Lewis Structure Lone Pairs

Lone pairs are pair of nonbonding electrons, which are not shared with other atoms through covalent bonds. Let us discuss it.

The lewis structure of CaS does not contain any lone pair. From the definition of lone pair, it is clear that the valence electrons which are not participating in covalent bond formation are defined as lone pairs.

Lone pair can be calculated from this formula = (Total number of valance electron – number of bonded electrons). As CaS is an ionic compound, there is no existence of any covalent bond as well as bonding electrons, therefore, lone pair cannot be calculated for CaS.

CaS Valence Electrons

Outer most shell electrons of any atom are known as valence electrons which are the most reactive with respect to the inner shell electrons. Let us find it.

The total number of valence electrons in CaS are 8. This can be obtained from the summation of the valence electrons of calcium and sulfur. Calcium has 2 electrons and sulfur has six electrons in their respective valence shell.

Calcium has electron configuration [Ar] 4s2 and sulfur has electron configuration in its valence shell 3s2 3p4. n=4 and n=3 is the outer most shell of calcium and sulfur respectively. Therefore, the electrons in n=4 orbital and n=3 orbital are regarded as valence shell electrons for calcium and sulfur.

CaS Hybridization

The concept of overlapping or mixing of two atomic orbitals is known as hybridization. Let us explain it in detail.

The term “hybridization” is not applicable for CaS. Overlapping of atomic orbitals can only be happened for any covalent molecule. Ionic bonds are formed due to electrostatic interaction between two oppositely charged ions. There is no overlapping of orbitals occurring in the formation of ionic compound.

Ionic bonds are formed due to the complete donation and acceptance of electron pairs between two atoms in the molecule. Therefore, hybridization has no contribution in forming an ionic bond like a covalent bond, which is formed due to orbital hybridization.

Is CaS solid?

Physical properties like the phase of solid, liquid and gas depend upon the nature of bonding and packing of the molecules. Let us give an overview on it.

CaS or calcium sulfide is definitely a solid substance. It has a white cubic and crystalline structure like the crystal of rock salt.

How CaS becomes solid?

CaS is presented as a solid substance because it has a closely packed structure. Due to this close packing, the intermolecular distance between the CaS molecules is very less and a huge amount of heat energy is required to break this close packing. Therefore, it is solid under room temperature.

Is CaS soluble in water?

Solubility in a particular solvent depends upon the nature of the solute and solvent. Let us discuss whether CaS is soluble in water or not.

CaS is soluble in water. The crystal of CaS is hygroscopic in nature which can attract the water molecules from air. It also reacts with water and form a mixture of Ca(SH)(OH), Ca(OH)2, Ca(SH)2. The reaction between CaS and H2O is – CaS + H2O = Ca(SH)(OH);  Ca(SH)(OH) + H2O = Ca(OH)2 + H2S.

How CaS becomes soluble in water?

CaS becomes soluble in water because of its polar nature and water is also a polar solvent. Ca2+ of CaS is surrounded by the positive end and S2- of CaS is surrounded by the negative end of water molecule. In this way CaS is hydrolysed by water molecule.

Is CaS polar or nonpolar?

Separation of opposite charge and the relative arrangement of the bonds are the reason of being a molecule polar or nonpolar. Let us explain it in detail.

CaS is definitely a polar molecule. It contains two oppositely charged Ca2+ and S2- ions, which make it a highly polar molecule.

How CaS becomes a polar molecule?

CaS becomes polar because of the presence of separation of the two opposite charge. Besides that, there is a huge electronegativity difference (2.58 – 1 = 1.58) between calcium and sulfur. If two atoms have electronegativity difference 1.8, then it is regarded as an ionic compound.

Is CaS acid or base?

Acidity or basicity depends upon the nature of the compound and the reactions in which the substance is participating. Let us discuss it in detail.

CaS is basic in nature. It shows basic pH in aqueous solution due to formation of strong base calcium hydroxide, Ca(OH)2 and weak acid, H2S.

How CaS becomes basic in nature?

CaS shows basicity and the aqueous solution of CaS shows weak basicity. When it is dissolved in water, a strong base calcium hydroxide and a weak acid, hydrogen sulfide is formed. The reaction is CaS + H2O = Ca(OH)2 + H2S.

Is CaS an electrolyte?

Dissociation into two oppositely charged ions in aqueous solution is defined as electrolysis. Let us talk about this in detail.

CaS is definitely an electrolyte. It can be dissociated into two oppositely charged ions, cation and anion after dissolving in water.

How CaS becomes an electrolyte?

CaS becomes an electrolyte because it is an ionic compound. CaS is consisted of two oppositely charged ions, Ca2+ and S2-. After dissolving in water, CaS is dissociated into these ions. Due to the dissociation into ions, ionic compounds can conduct heat and electricity.

Is CaS salt?

Salt, an ionic compound consisting of one cation (except H+) and one anion (except OH) is obtained from the neutralization reaction along with water. Let us discuss it.

CaS is definitely a salt as it is an ionic compound. Salts are formed due to the electrostatic attraction force between two oppositely charged ions.

How CaS becomes a salt?

CaS is a salt which contains two oppositely charged ions, calcium (Ca2+) and sulfide (S2-). It is consisted of two opposite ions other than H+ and OH. When it is dissolved in water, CaS is broken into these two ions.

Is CaS ionic or covalent?

Ionic or covalent character can be decided from the nature of the bond whether it is formed by the sharing or completely transferring of electron pairs. Let us explain it.

CaS is certainly an ionic compound due to the presence of two ions. These ions are attached with each other through electrostatic force of attraction.

How CaS becomes an ionic compound?

CaS becomes an ionic compound as the bond between calcium and sulfur is formed due to the completely transferring of electron pairs from calcium to sulfur. Besides that, CaS is formed between the attraction of one metal (Ca) and one nonmetal (S). This is an important property of any ionic compound.


Calcium sulfide, has different uses in different fields like phosphors, lubricant additives, and luminous paints. It is also used in ore dressing and flotation agent and reacts with elemental sulfur to produce lime-sulfur.

Aditi Roy

Hello, I am Aditi Ray, a chemistry SME on this platform. I have completed graduation in Chemistry from the University of Calcutta and post graduation from Techno India University with a specialization in Inorganic Chemistry. I am very happy to be a part of the Lambdageeks family and I would like to explain the subject in a simplistic way. Let's connect through LinkedIn-

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