The chemist envision reaction take place when molecules/atoms collide with respect to the correct amount of energy and in the correct position so that the bond can be formed.These means that the reaction take place when two or more molecules collides and a reaction occurs.
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the terminator because i did this test
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Potassium (K) has a larger average atomic radius (220 pm) than sodium (Na) does (180 pm). The potassium atom has an extra electron shell compared to the sodium atom, which means its valence electrons are further from the nucleus, giving potassium a larger atomic radius. The ionic radius increases in a particular group on moving from top to bottom due to increase in the principle energy shell though the number or electrons in the valence shell remain the same
A melting point of over 700 C and a density of less than 2 g/cm3 can be observed for many group 2 elements. In this group, the density increases on moving down the group, whereas the melting point increases upto calcium and then starts decreasing.
Calcium, symbol Ca is the element with melting point around 840 C and density of 1.55 g/cm3 which is closest to the specified data range .