Arrange the following atoms in order of increasing ionization energy: lithium, oxygen, magnesium, strontium, chlorine, and tellurium. Explain your order.

Ionization energy is the energy required to remove the most loosely bound electron from the last shell.

In the periodic table, there are groups and periods.

In a period, the ionization energy increases as we move across a period as the size decreases. The electrons get added to the same shell and the nuclear charge increases.

The valence shell moves nearer to the nucleus.  Thus more energy is required to remove the valence electron.

In a group, the ionization energy decreases from top to bottom as we move down a group.

The size increases as the electrons get added up in the new shell, the electron in the outermost orbital gets far away from the nucleus. And hence, the electron will be easier to remove. Thus, lesser energy is required to remove the valence electron.

The correct order of increasing ionization energy is:

lithium < strontium < magnesium < tellurium < chlorine < oxygen

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lithium < strontium < magnesium < tellurium < chlorine < oxygen  

Explanation:

Ionization energy is the energy required to remove the most loosely bound electron from an isolated gaseous atom.

In a period, the ionization energy increases as we move across a period as the size decreases. The electrons get added to the same shell and the nuclear charge increases.The valence shell moves nearer to the nucleus.  Thus more energy is required to remove the valence electron.

In a group , the ionization energy decreases from top to bottom as we move down a group. The size increases as the electrons get added up in the new shell, the electron in the outermost orbital gets far away from the nucleus. And hence, the electron will be easier to remove. Thus, lesser energy is required to remove the valence electron.

The correct order of increasing ionization energy will be:

lithium < strontium < magnesium < tellurium < chlorine < oxygen  

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.