Which element can expand its valence shell to accommodate more than eight electrons? which element can expand its valence shell to accommodate more than eight electrons? o he n br?

Br can expand its valence shell to accommodate more than eight electrons.

Explanation:

In a bond, elements tends to accommodate their valence electrons to reach the configuration of a noble gas (The Octet rule), so they try to complete their valence shell with 8 electrons, and they can do that only if they use the orbitals s (may contain only 2 electrons) and p (may contain only 6 electrons).

Sometimes, there are elements that need to share more than 8 valence electrons to use all the available electrons, but this is possible only if the atom has orbitals d (may contain 10 electrons) or f (may contain 14 electrons).

That's why only the elements that has a number 3 of period or more can expand its valence shell, because level 3 atoms has a d subshell.

In this case, He atom is in period number 1, N atom is in period number 2 and Br atom is in period number 3, that's why Br atom can expand its valence shell, and He and N atoms can't.

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol