Explain the trend in atomic radii from Lithium to Fluorine?

As we go from Li to F, atomic radius of the atoms will DECREASE. This is due to increased nuclear charge (number of protons within each atom). Although the number of electrons also increases, each additional electron is placed within the same electron shell, so all the electrons are the same distance from the nucleus. This means the increased nuclear charge has a greater force of attraction on the electrons, drawing them closer to the nucleus, hence causing a decrease in atomic radius.