So, Is CaF2 ionic or covalent? CaF2 is an ionic compound because, in the CaF2 molecule, calcium acts as a cation by donating its 2 extra electrons from the valence shell, and Fluoride acts as an anion by accepting the electrons from Calcium, completing its octet. Therefore, Calcium and fluoride together form an ionic bond, i.e., CaF2. The bond angle between CaF2 is 154 degrees. The pair of fluorine atoms are bonded with the one atom of Calcium and are held together by electrostatic forces of attraction, resulting in an ionic bond between Calcium and fluoride. The bond between them can be ionic or covalent depending upon the charge spread over the molecule and its structure. If there is sharing of electrons in the valence shell of the bonded atoms, it would be covalent bonding, and if a complete transfer of electrons from one atom to another takes place, it is called ionic bonding.
Why is CaF2 Ionic?
CaF2 is formed by electron exchange between one molecule of Calcium and two molecules of fluoride. The outermost shell of Calcium has 2 electrons, whereas fluoride is a deficit of 1 electron, or fluoride has 7 electrons in its valence shell. Thus, to attain a stable ionic configuration, Calcium has to lose its 2 valence electrons, and fluorine needs one extra electron in its valence shell. Therefore, Calcium acts as a cation by donating its 2 electrons and attaining an inert gas configuration. At the same time, the two atoms of fluorine accept one electron from Calcium and form a stable configuration of CaF2. The three ions, i.e., one of calcium and two of fluorine, combine as an ionic crystal and are held together by electrostatic forces of attraction. Since CaF2 is an ionic bond and ionic bonds are non-directional. Hence, the structure of CaF2 is neither bent, not linear.
The net charge present on the CaF2 molecule
To calculate the net charge of any compound, use the formula, Net Charge = (number of Valence Electron) – (number of Unbonded Electrons + number of Half Of The Bonded Electrons) The number of valence electrons: Fluorine has 7 valence electrons, but there are 2 fluorine atoms in the molecule, making it a total of 14 electrons for the fluorine atoms. On the other hand, the Calcium atom has two electrons in the valence shell, making it a total of 16 valence electrons. Bonded electrons: Two electrons from calcium and two electrons one from each fluorine makes it 4 bonded electrons. You can also count bonds in the atom instead. Unbonded electrons: Total unbonded electrons in the molecule are 12. Thus, according to the formula, Net charge = 14(V.E) – 12(unbonded electrons) – 2(half of bonded electrons) As per the above formulae, there exists zero charge on the molecule.
CaF2 Molecular Structure
The CaF2 compound is ionic, the Fluoride ions are in a cubic arrangement, and calcium ions are placed in half cubic sites of the shape.
In the above diagram, red color dots represent calcium ions, whereas green color dots represent fluoride ions.
Lewis Structure of CaF2
Calcium is an alkaline earth metal, whereas Fluorine is a non-metal. When a metal and nonmetal combine, it forms an ionic compound. Ca being in group 2 has 2 valence electrons, whereas F being in group 17 has 7 valence electrons.
Metals and non-metals tend to complete their octet. F has seven electrons, which means it requires just one electron in its valence shell to complete its octet. Whereas Ca gives its 2 electrons to F, thus completing its octet.
But Calcium is still left with an electron. Similarly, through one more Florine with 7 valence electrons, the octet rule for both Ca and F can be satisfied.
The Resulting Lewis structure will be as below.
What is the structure of CaF2?
CaF2 is made from 2 fluoride molecules and 1 calcium molecule. It forms a structure similar to the cube. Electrons of CaF2 are in 3d orbitals, and the movement of these electrons occurs in between dyz and dz2. CaF2 is linear in shape and is most stable when the electrons are in dz2 orbitals and are bent in shape when the electrons are in dyz orbitals.
Ionic vs Covalent Compounds
The concept of ionic and covalent compounds is a bit confusing. Let us understand the concept of ionic and covalent compounds by understanding their basic definitions. Ionic compounds are those compounds that have molecules of charged ions. These charged ions are oppositely charged ions, i.e., positive and negative. Covalent compounds are the non-metals bound together, consisting of two electrons shared between two atoms. The molecular forces of attraction in the case of the ionic compounds to form the ionic bond is the electrical force of attraction between the cation and the anion of the molecule. Cations are the positively charged ions, whereas anions are the negatively charged ions. Cations are metals, and anions are non-metals. Whereas, in a covalent bond, the sharing of electrons takes place between atoms.
Factors Influencing the Formation of Ionic Bond
Three factors influence the formation of the ionic bond. These factors are electron affinity, ionization energy, and lattice energy, which are explained below.
Electron Affinity Electron affinity refers to the energy released when an electron is added to the isolated gaseous atom. In the process of an ionic compound, the atoms form into an anion through gaining electrons. This formation of anion favors higher electron affinity.
Ionization energy Ionization energy refers to the energy which is required to remove the loosely bound electron of the atom. It happens when the gas atom is in free space isolated from other atoms.
Lattice energy Lattice energy is the release of energy when the cation and anion are attracted. They are attracted as they have opposite charges. The higher amount of lattice energy released, the more is the tendency of the formation of an ionic bond.
How is CaF2 Prepared?
The preparation steps of calcium fluoride are as below:
- Provide waste solution comprising of HF acid
- Control the HF content within a predetermined concentration range in the waste solution
- Add Ca source in the waste solution with HF acid within a predetermined concentration range.
- Control the reaction temperature of Ca and HF to form CaF2 within a predetermined temperature range.
The advantage of preparing CaF2 by this method are:
It is a simple process, low in cost, high preparation speed, stable purity, and high quality of the CaF2 prepared. Use the manufacturing process for cleaning at the wafer as HF acid is taken in large amounts. The useless HF acid that is discharged is the least amount. The cleaning process will use pure water to clean again. This way, more HF acid waste liquid will be prepared. HF acid liquid waste must be prepared with recovery so that less pollution and harm is caused to the environment. The general processing of CaF2 requires HF which is acidic in nature. HF is then reacted with an alkalic compound of Ca for neutralization, resulting in the formation of salt and water. However, the process is very difficult and costly. Other fluoride compounds are also released which are of no use, except for sludge treatment.
Conclusion
CaF2 is an interesting compound that is linear in shape. The bond angle is 0 degrees with a net charge of 0 on the molecule. It is insoluble in water and exists in nature as fluorite. Being ionic, it shows some properties of ionic compounds such as closed packed cubic structure, high melting and boiling points, and others. The compound can be easily understood by carefully examining the Lewis structure of the compound.
