BeH2 or berilium hydride is a linear compound with a bond angle 1800. The appearance of this compound is a white orthorhombic crystalline solid. The shape of the crystal is hexagonal with a very much high density 0.78 g.cm-3. In this compound, beryllium is attached with the two hydrogen atoms with two covalent bonds.
BeH₂ (Beryllium hydride) features a linear Lewis structure: a central beryllium (Be) atom with 2 valence electrons forms single bonds with two hydrogen (H) atoms, each contributing 1 valence electron. The molecule uses 4 valence electrons total. BeH₂ has no lone pairs on the Be atom, resulting in a 180° bond angle. Electronegativity values: Be (1.57), H (2.20), suggesting polar covalent bonds. However, the molecule’s linear geometry leads to an overall nonpolar structure.
Let’s focus on the following topics described below.
How to draw BeH2 lewis structure?
Lewis structure is nothing but a structural representation of any molecule with the nonbonding electrons around the respective atoms. The steps of drawing this structure are explained below-
- Finding out the valance electrons: In BeH2, Be is a s-block element and it has two valance electrons in its 2s orbital. Hydrogen has only one electron in its 1s orbital and this is the only outer most shell electron of hydrogen.
- Determination of bonds and bonding electrons: Total two covalent bonds are present between Be and two hydrogen atoms in BeH2 molecule. Thus, the number of bonding electrons are 2×2=4.
- Finding out the nonbonding electrons: In BeH2, all the valance electrons of Be are used up in bonding with hydrogen. So, no electrons are left as nonbonding electron pairs.
BeH2 Lewis Structure Shape
The hybridization of the central atom plays the most important role to predict the structure or shape of any molecule. Besides that, the repulsive factor involving lone pairs and bond pairs. These repulsions are known as-
- Lone pair- lone pair repulsion
- bond pair-bond pair repulsion
- lone pair-bond pair repulsion
The increasing order of the above repulsive factor is-
bond pair -bond pair repulsion < Lone pair – bond pair repulsion < Lone pair- lone pair repulsion.
BeH2 is one of the most simplest molecule in which no lone pairs are present on central atom, Be. Be has two electrons in its outer most shell which are totally used up to form the two covalent bonds with two hydrogen atoms. Thus, the above repulsive factors become insignificant to determine the structure. Due to absence of any repulsions BeH2 shows its actual geometrical structure and actual bond angle.
In this molecule, beryllium is sp hybridized with two bond pairs. The geometry of this molecule is linear with a bond angle 1800.
BeH2 Lewis Structure Formal Charge
Formal charge is the theoretical charge on each of the atom of any molecule and it is assumed that electrons are shared between all the atoms irrespective pf electronegativity.
- Formal charge = Total number of valance electrons – number of electrons remain as nonbonded – (number of electrons involved in bond formation/2)
- Formal charge on beryllium, Be = 2 – 0 – (4/2) = 0
- Formal charge on each of the hydrogen atom, H = 1 – 0 – (2/2) = 0
Formal charge of each of the atom in BeH2 molecule is zero. Thus, it is a neutral molecule with no charge.
BeH2 Lewis Structure Angle
Structure angle is basically the angle between two bonds. Hybridization of central atom also determines the bond angle of any molecule. In some times lone pairs – lone pair repulsion and lone pair-bond pair repulsion also have impact on determining the molecular structure.
In this BeH2 molecule, beryllium is sp hybridized and does not have any remaining electrons as nonbonded. Thus, the molecule shows its actual bond angle. Sp hybridization of central atom directs the bond angle to be 1800 and structure to be linear shaped.
Two Be-H bonds are aligned with the angle 1800 with each other keeping maximum distance between them.
BeH2 Lewis Structure Octet Rule
Octet rule is one of the most significant rule in chemistry. It states that any molecule should contain eight valance electrons in their respective valance shell to achieve the nearest noble gas like electron configuration.
Octet rule is violated in BeH2. Since beryllium has only two electrons in its valance shell, 2s orbital. After bonding two hydrogen atoms it gains two more electrons. But eight electrons of octet rule can’t be achieved by beryllium. Thus, it can’t have the electron configuration like its nearest noble gas of periodic table neon, Ne (2s2 2p6).
BeH2 Lewis structure Lone Pairs
Valance electrons of any atom are basically two types-
- Electrons involved in bonding (bonding electrons)
- Nonbonding electrons or lone pair.
Those valance electrons do not participate in bond formation are defined as nonbonding electrons or lone pairs.
- Nonbonded electron = Total number of valance electron – number of bonded electrons.
- Nonbonding electrons on Be = 2 – 2 = 0
- Nonbonding electrons on each of the H atom = 1 – 1 = 0
Thus, BeH2 has no lone pairs or nonbonding electrons in its structure.
BeH2 Valence Electrons
Valance electrons are defined as the outer most shell electrons. These electrons are most loosely bound to the nucleus. So, nuclear attraction force on these electrons is minimum with respect to the inner shell electrons.
In most of the cases valance electrons are most reactive and they participate in different chemical reactions due to the least attraction force of nucleus on them.
Be has total 4 electrons in this manner, 1s2 2s2. So, the number of valance electrons of Be are 2 (2s is the valance shell) and 1 for hydrogen (1s1). These two electrons of Be and one electron of hydrogen are involved in two covalent bond formation. Thus, total number of valance electrons in BeH2 are = {2+(2×1)} = 4
BeH2 Hybridization
Hybridization is nothing but the mixing of two atomic orbitals to generate a new orbital. It is the most important parameter of determining the molecular shape. How can we detect the molecular shape from hybridization is shown in the following table.
| Hybridization of central atom | Structure |
| sp | Linear |
| sp2 | Trigonal planar |
| sp3 | Tetrahedral |
| sp3d | Trigonal bipyramidal |
| sp3d2 | Octahedral |
From the above picture it is clear that Be is sp hybridized in this molecule. Two valance electrons of Be and one valance electron of each of the hydrogen are responsible for this sp hybridization. On s and one p orbital participate to form the mixing sp orbital in BeH2 molecule.
The % contribution of both the s and p orbital is 50 in sp hybridization.
BeH2 Solubility
BeH2 or beryllium hydride is an alkaline earth hydride which is insoluble in solvents that do not decompose this compound.
It decomposes in water and that is why it is soluble in water but it has no solubility in diethyl ether and toluene.
Is BeH2 ionic?
No, BeH2 is a covalent compound due to having two covalent Be-H bonds. It is not an ionic compound because-
- Both the participating atom, Be and H are nonmetal.
- The bonding electrons are shared between two beryllium and hydrogen, not entirely transferred from one atom to another atom.
- Melting point is also not so high, 2500 C or 523K.
Is BeH2 polar or nonpolar?
Polarity of any molecule depends upon the two following parameters-
- Bond moment of each bond present in the molecule
- Orientation of the bond connecting central atom and substituent atoms.
In BeH2, both the Be-H bonds are polar due to having electronegativity difference between Be and H. But these two bonds are aligned with an angle 1800.
Due to having this anti-parallel structure one bond moment is cancelled out by the another and the dipole moment becomes zero. Thus, BeH2 is a nonpolar molecule.
Is BeH2 acidic or basic?
BeH2 is basically a lewis acid. Lewis acids are those molecule which can accept the electron pairs in their vacant orbital.
Be is an electron deficient atom because it has vacant 2p orbital which can easily accommodate electron pairs from any electron rich compounds or base. Thus, it acts like a lewis acid and show acidic properties.
Conclusion
Different facts of structure and bond angle with some explanations are explained through this article. We have come to know that BeH2 is a linear crystalline water soluble compound with zero dipole moment.
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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.
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