Chuck wants to know how many electrons in an atom are not paired up. which model would be best for chuck to write out?

a set of quantum numbers for the last electron in the atom
a configuration with numbers, letters, and superscripts
a dot structure of the atom
an orbital notation of the atom

The best model which Chuck will use is an orbital notation of the atom.

Explanation: Orbital notation of an atom is described as the arrangement of electrons in the orbitals present in an atom.

This is also known as the electron configuration.

This notation follows Hund's rule which states that the every orbital in the given subshell will be singly occupied first, until one electron gets paired up.

So, the orbital notation of an atom will make Chuck know how many electrons are not paired up.

The model, which will be best for Chuck to use is AN ORBITAL NOTATION OF THE ATOM.

An orbital notation refers to a mean of writing the electronic configuration of elements in such a way that they provide more detailed information about the electrons that are present in an element. Orbital notation uses blank to represent orbitals and arrows to represent electrons. Orbital notation can also be used to determine the quantum number of an electron.

increased stability in the completion of fluorine's outer shell.

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.