Trends: 1. Across? ?the? ?period ? There? ?is? ?a? ?general? ?decrease? ?in? ?atomic? ?radius? ?across? ?the? ?period. - Across? ?a? ?period,? ?proton? ?number? ?increases? ?and? ?electrons? ?are? ?being? ?added? ?to? ?the? ?same? ?outermost principal? ?quantum? ?shell - Forces? ?of? ?attraction? ?between? ?the? ?valence? ?electron? ?and? ?nucleus? ?increases? ?as? ?nucleus? ?becomes more? ?positively? ?charged - Distance? ?between? ?the? ?valence? ?electron? ?and? ?nucleus? ?decreases. 2. Down? ?the? ?group ? There? ?is? ?a? ?general? ?increase? ?in? ?atomic? ?radius? ?down? ?the? ?group - Number? ?of? ?filled? ?principal? ?quantum? ?shell? ?increases