Beryllium Lewis structure

A few examples will illustrate how VSEPR is used to predict molecular geometry. Beryllium chloride, BeCl, has the Lewis structure... 

Draw the Lewis structure for beryllium hydride, BeH2. Draw the orbitals that overlap in the bonding of BeH2, and label the hybridization of each orbital. Predict the H—Be — H bond angle. 

As we saw in Section 18.1, the small size and relatively high electronegativity of the beryllium atom causes its bonds to be more covalent than is usual for a metal. For example, beryllium chloride with the Lewis structure... 

Elements in groups 2A and 3A of the periodic table, such as beryllium and boron, do not have enough valence electrons to form an octet in a neutral molecule. Lewis structures for BeH2 and BF3 show that these atoms have only four and six electrons, respectively, around the central atom. There is nothing we can do about this There simply aren t enough electrons to form an octet. 

You may have to try several Lewis structures until you get one in which all of the atoms, except hydrogen, beryllium, and boron, obey the octet rule. 

In some compounds the number of electrons surrounding the central atom in a stable molecule is fewer than eight. Consider, for example, beryllium, which is a Group 2A (and a second-period) element. The electron configuration of beryllium is ls 2s it has two valence electrons in the 2s orbital. In the gas phase, beryllium hydride (BeH2) exists as discrete molecules. The Lewis structure of BeH2 is... 

The octet rule predicts that atoms form enough covalent bonds to surround themselves with eight elechons each. When one atom in a covalently bonded pair donates two electrons to the bond, the Lewis structure can include the formal charge on each atom as a means of keeping track of the valence electrons. There are exceptions to the octet rule, particularly for covalent beryllium compounds, elements in Group 3A, and elements in the third period and beyond in the periodic table. 

The Lewis structure of beryllium chloride in the gaseous state is... 

Draw the Lewis structure of beryllium hydride, BeH2. 

Molten beryllium chloride reacts with chloride ion from molten NaCl to form the BeCl4 ion, in which the Be atom attains an octet. Show the net ionic reaction with Lewis structures. 

A second type of exception occurs when there are fewer than eight valence electrons around an atom in a molecule or polyatomic ion. This situation is also relatively rare (with the exception of hydrogen and helium as we have aheady discussed), most often encountered in compounds of boron and beryllium. As an example, let s consider boron trifluoride, BF3. If we follow the first four steps of our procedure for drawing Lewis structures, we obtain the structure... 

AB2, Ns = 2 beryllium chloride (BeCl2). The Lewis structure of the molecule beryllium chloride is... 

Solution (a) The central atom is beryllium (Be). The Be atom has two valence electrons with a ground-state electron configuration of [He]2s. The Lewis structure of BeH2 is... 

Molecules with Electron-Deficient Atoms Gaseous molecules containing either beryllium or boron as the central atom are often electron deficient they have fewer than eight electrons around the central atom. The Lewis structures, with formal charges, of gaseous beryllium chloride and boron trifluoride are... 

Lewis structure and molecular shape of beryllium chloride... 

Consider the gaseous beryllium chloride molecule, BeCl2(g) The Lewis structure of the molecule shows there are only two electron pairs (two electron domains) in the valence shell of the beryllium atom (Figure 4-44). These two pairs of electrons try to separate as far as possible from each other so as to minimize electron repulsion. Thus, the beryllium chloride molecule adopts a linear shape with a bond angle of 180°, because the electron pairs are ferthest apart when they are on opposite sides of the beryllium atom. 

Draw the Lewis structure for BeCl2. (Hint Beryllium atoms do not follow the octet rule.)... 

The bonding in gas-phase beryllium chloride shown as (a) a Lewis structure,... 

The beryllium atom in BeCl2 is electron-defident (only four valence electrons surround it), which makes it very reactive toward electron-pair donors such as ammonia. Draw a Lewis structure for the expected product when BeCl2 reacts with excess ammonia. 

The structure of dimethylberyllium is similar to that of trimethylaluminum except for the fact that the beryllium compound forms chains, whereas the aluminum compound forms dimers. Dimethylberyllium has the structure shown in Figure 12.3. The bridges involve an orbital on the methyl groups overlapping an orbital (probably best regarded as sp3) on the beryllium atoms to give two-electron three-center bonds. Note, however, that the bond angle Be-C-Be is unusually small. Because beryllium is a Lewis acid, the polymeric [Be(CH3)2] is separated when a Lewis base is added and adducts form. For example, with phosphine the reaction is... 

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