The closest planet to the sun is Mercury. After Mercury the order of the planets is Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Before Pluto was demoted from its planetary status it was after Neptune.
Mercury is the first planet from the sun yet it is not the hottest planet in the solar system. The daytime temperatures on Mercury are around 800 degrees Fahrenheit. At night, the temperatures drop dramatically and reach freezing temperatures of -280 degrees Fahrenheit. The planet's drastic difference in temperature is due to the fact that Mercury has a very tiny atmosphere and its atmosphere is unable to retain the heat energy it receives from the sun. Venus, with its thick atmosphere, is the hottest planet.