Why on hot days the mercury inside a thermometer moves up and on cooler days it moves downs

When it is hot, the heat causes the mercury inside the thermometer to expand, and so that is why it moves UP.
However, when it's cold, the cold causes the mercury inside the thermometer to contract, and so that is why it moves DOWN.

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.