Elements in the periodic table show a trend in atomic radius. State and explain the trend in atomic radius from Li to F.

The atomic radii of an atom is essentially the distance from the centre of the nucleus to the outer shell of electrons- so atoms that are very small and have a small distance from the nucleus to the outer shell can be described as having a small atomic radius. There are clear patterns in atomic radii going down groups in the periodic table and across periods. Going across the periodic table in the period of Li to F, the atomic radii of atoms decreases. From Li to F the number of protons in the atoms increases (seen on the periodic table by an increase in the atomic number), and this has the effect of increasing the nuclear charge of the atom and increasing the nuclear attraction between the positively charged nucleus to the negatively charged orbiting electrons. As a result, the electrons are more stongly pulled in towards the nucleus leading to the smaller atomic radius. It is also worth mentioning that from Li to F, the outer electrons are in the same shell so experience the same shielding effect (recall that the shielding effect is electrons repelling each other between shells)- so the number of electron shells is not a contributing factor.