Why don’t we draw double bonds betweens the Be atom and the Cl atoms in BeCl2?

good question…I’d go with (e)

****** here’s why ********

start by drawing a lewis dot structure..

chlorine has 7 valence electrons and Beryllium has 2 valence electrons.

:Cl:Be:Cl:

plus the two electrons above and below each Cl atom. I can’t draw those here.

the only way to get double bonds between Cl and Be is to take two electrons from each Cl, give one to the Be and keep the other at Cl to use for a bond.. like this.

Cl::Be::Cl

again. with two more electrons above and below each Cl.

****

now let’s look at the possible answers…

a). nope. there are 8 electrons around Be

b)…nope. 8 electrons around Cl

c)…nope. 4+2×17 = 38 electrons.. 4+22*17 = 38 protons. charge= 0

d)…nope. plenty of electrons

leaves (e)… and this is true because each Cl now has 4 electrons of it’s own and 1 from each of the two double bonds for a total of 6 valence electrons + the 10 non valence electrons gives it 16 electrons and 17 protons and a formal (+1) charge. Be now has a formal (-2) charge. 1 electron from each of 4 bonds + the 2 non valence electrons = 6 electrons. 4 protons. -2 charge.

More importantly, and the reason we don’t give Cl and (+1) charge is this. Cl has a much higher electronegativity than Be.. 3.16 vs 1.57. Meaning it won’t give up that extra electron to Be.

fyi, the rules of covalent vs polar covalent vs ionic are

(1) ∆EN <0.5 = non polar covalent

(2) <0.5 ∆EN <1.6 = polar covalent

(3) 2.0 < ∆EN = ionic

(4) 1.6 < ∆EN < 2.0.. is ionic if a metal is involved, is polar covalent if no metal is involved.

∆EN for BeCl2 is 1.59..this is polar covalent by rule (2) and borderline ionic by rule (4). Turns out this molecule actually polymerizes to form a linear polymer. It doesn’t exist in a crystal lattice, it’s a polar covalent molecule.

The bonding in BeCl2 does have covalent character, since Be is such a small atom. We don’t draw double bonds because it would put a positive one formal charge on each Cl. Chlorine happens to be an element that has fairly high electronegativity. So we minimize formal charge and let beryllium (just like boron) be an exception to the octet rule. Its electron deficiency makes it a good Lewis acid.

Well Be & Cl don’t have a covalent bond for a start.

Be and Cl have an ionic bond Beryllium will gain a charge of 2+ and for every one Beryllium there a two chlorine ions with a charge of 1-.

It’s written like this: [Be2+] , 2[Cl-]

Be has 2 elections in outer shell

Cl has 7 and needs 8 to get a full shell and become stable.. there are 2 Cl’s so each one gets one from the Be atom. and there is a single bond between each Cl and Be

Cl — Be — Cl

Be is one of the atoms that breaks the octet rule in chemistry, along with Iodine and another one. Beryllium is “happy” with 4 electrons on it’s outermost energy level and does not require eight.

I would say it’s c… (I believe the better way to explain is by the following).

Cl(1-) ↔ Be(2+) ↔ Cl(1-)

Each of the 2 bonds (electrons of the Be ion) is ionically bonded to 1 bond of two chlorine Ions to form BeCl2.

Yea, Beryllium is a metal, CL is a nonmetal, so they form an ionic bond.

Only elements that covalently bond can double or triple bond. The most common elements that do this are N,O,C,F,S. covalent bonds are creating with molecular elements.

boom thats why