Which electrons are removed from the outermost shell of a calcium atom, the atom becomes
a)an anion that has a larger radius than the atom
b)an anion that has a smaller radius than the atom
c)a cation that has a larger radius than the atom
d)a cation that has a smaller radius than the atom

Answer is: D) a cation that has a smaller radius than the atom.

Atomic number of calcium is 20, it means that it has 20 protons and 20 electrons, so atom of calcium is neutral.  

When calcium lost two electrons, it will have 20 protons (positive charge) and 18 electrons (negative charge), which means it has two protons more and it has +2 oxidation number.

Electron configuration of calcium atom: ₂₀Ca 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

Electron configuration of calcium cation: ₂₀Ca²⁺ 1s² 2s² 2p⁶ 3s² 3p⁶.

Calcium cation is smaller than neutral calcium atoms, because when an electrons are lost, electron-electron repulsion decreases and the protons are better able to pull the remaining electrons towards the nucleus.

Answer is: D) a cation that has a smaller radius than the atom.

Atomic number of calcium is 20, it means that it has 20 protons and 20 electrons, so atom of calcium is neutral.  

When calcium lost two electrons, it will have 20 protons (positive charge) and 18 electrons (negative charge), which means it has two protons more and it has +2 oxidation number.

Electron configuration of calcium atom: ₂₀Ca 1s² 2s² 2p⁶ 3s² 3p⁶ 4s².

Electron configuration of calcium cation: ₂₀Ca²⁺ 1s² 2s² 2p⁶ 3s² 3p⁶.

Calcium cation is smaller than neutral calcium atoms, because when an electrons are lost, electron-electron repulsion decreases and the protons are better able to pull the remaining electrons towards the nucleus.

petroleum? coal maybe?

vanderwaal's forces of attraction are the electrostatic intermolecular forces that exist in a molecule due to the temporary or permanent dipoles that are developed in a molecule. in , the major intermolecular forces are dipole-dipole interactions as the molecule is polar (bent structure). so the vanderwaal's forces of interaction in between molecules are the permanent dipole-dipole interactions that develop due to the dipole that exists in between the polar h - s bond. the positively charged hydrogen atom is attracted towards the negative end of the dipole that is sulfur of the adjacent molecule. therefore, these forces of attraction are relatively stronger than that of london dispersion forces that exist in non polar molecules.