Electrons are emitted from the surface of a metal when it's exposed to light. This is called the photoelectric effect. Each metal has a certain threshold frequency of light, below which nothing happens. Right at this threshold frequency, an electron is emitted. Above this frequency, the electron is emitted and the extra energy is transferred to the electron. The equation for this phenomenon is KE=hv-hv0 where KE is the kinetic energy of the emitted electron, h=6.63x10^-34 J. s is Planck's constant, v is the frequency of the light, and v0 is the threshold frequency of the metal.
Also, since E=hv, the equation can also be written as KE=E-E0
where E is the energy of the light and E0 is the threshold energy of the metal.
Here are some data collected on a sample of cesium exposed to various energies of light.
Light energy Electron emitted? Electron KE
(eV ) ( eV)
3.87 no __
3.88 no __
3.89 yes 0
3.90 yes 0.01
3.91 yes 0.02
What is the threshold frequency v0 of cesium?
Note that 1 eV (electron volt)=1.60x10^-19 J.
Express answer in hertz

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

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