For the same reason electronegativity – the degree to which an element tends to gain electrons – increases from left to right. More protons means that electrons are pulled in more tightly toward the nucleus. Moving from the left side of the period to the right, the atomic radius becomes smaller because each element has one additional proton and one additional electron. The horizontal rows of the table are called periods. This is important because how elements interact and react with each other depends on their ability to lose and gain electrons to make new compounds. But the amount of energy needed to rip off an outer electron decreases going from the top to the bottom because the electrons are farther from the nucleus and not held as tightly. Going from the top of Group I to the bottom, for example, the atomic radii – the distance from the nucleus to the outer electrons – increases. And the properties can be assumed based on the location within the group. Elements in the same group share similar properties. By studying the behavior and trends of Group I elements, we can get a glimpse of how the periodic table is arranged and how to interpret it.Įach of the 18 columns in the table is called a group or a family. I am a chemist who spent his career building new molecules, sometimes using Group I elements. Not only are they very reactive, they are soft and shiny, can easily be cut even with a dull knife and are the most metallic of all known elements. For further dramatic effect, I also placed some potassium into water and astonished everyone with the explosive bluish flames.īecause Group I metals, also known as alkali metals, are very reactive, like the sodium from the rail car or the potassium, they are not found in nature in pure form but only as salts. While on the air I added some sodium to a bit of water in a petri dish and we observed the vicious reaction. A television reporter called me for an explanation of why firefighters were not allowed to use water on the flames bursting from the mangled car. The news broke that a railroad car, loaded with pure sodium, had just derailed and was spilling its contents.
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