The allowed energies of a simple atom are 0.0 ev, 5.5 ev and 9.0 ev . an electron traveling at a speed of 1.8×106 m/s collisionally excites the atom. part a what is the minimum speed the electron could have after the collision?

The possible transitions of the electrons are from 0.0 ev to 5.5 ev and from 5.5 ev to 9.0 ev.

The minimum change in energy is from 5.5 to 9.0 equal to 4.5 ev.

Then, we need to find the speed of the electron to gain a kinetic energy of 4.5 ev from the equation KE = (1/2)m*v^2

Where,

KE = 4.5 ev * 1 J / (6.242*10^18) ev  = 7.2098 * 10^ - 19 J

m = mass of the electron =  9.11 * 10 ^ -31 kg

v = √ (2 * KE/m) = √[ 2*7.2098* 10 ^ -19 kg / (9.11*10^-31kg) = 1,258,107 m/s

1,258,107 m/s

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -