The orbit of Mercury is the most eccentric of the planets in our Solar System. The planet has an orbital period of 87.969 Earth days. At perihelion it is 46,001,200 km from the Sun and at aphelion it is 69,816,900 km, a difference of 23,815,700 km giving it an eccentricity of 0.21. Mercury’s orbit is inclined by 7 degrees to Earth’s ecliptic. Mercury can only be seen crossing the face of the Sun when the planet is crossing the plane of the ecliptic and is between the sun and Earth. This happens about once every seven years.
Source: Orbit of Mercury – Universe Today
A more precise value of the eccentricity of Mercury’s orbit is 0.205 630. By comparison, the eccentricity of Earth’s orbit is 0.0167086, and the eccentricity of the orbit of Venus is 0.006772.
Mercury is locked in a 3:2 spin-orbit resonance making three rotations about its spin axis every two orbits about the sun. Because of this, if you were on the surface of Mercury, the Sun would pass overhead once every two orbits around the Sun, or 176 Earth days. In other words, one day on Mercury (sunrise to sunrise) takes two Mercury years. A Mercury year takes 88 Earth days, the length of time to orbit the Sun.
Source: Mercury’s Orbit
So one solar day on Mercury is about 176 Earth days, and one “Mercury day” (a sidereal day or the period of rotation of Mercury around itself) is equal to approximately 58.7 Earth days.
And there is also the precession of the perihelion of Mercury. The closest distance of Mercury from the Sun doesn’t happen at the same place but moves slowly around the Sun. The other planets of the solar system have perihelion shifts, but classical mechanics did not give an accurate value of Mercury’s perihelion precession. The General theory of Relativity was able to show and predict that Mercury’s orbit shifts by about 43 seconds of arc per century.