You are possibly getting confused by the fact Russia was not the Soviet Union but, as RSFSR, one of it's constituent republics.

Stalin, Malenkov, Khrushchev, Brezhnev, Andropov, Chernenko, Gorbachev were all general secretaries of the Central Committee of the Communist Party of the Soviet Union.

"Head of state" (i.e. President, a mostly ceremonial post until 1977) is the wrong thing to be looking for. Stalin and Khrushchev were never head of state, though each was for a time head of government (prime minister). After Lenin, top leadership went with the post of general (or first) secretary of the Party. The "list of leaders" is the one you want, though Stalin's takeover was a more gradual process from the creation of the general secretaryship and Lenin's illness in 1922 to the defeat of the left opposition in 1927 and the right in 1929.

And yes, it's very important to differentiate between the USSR and Russia, which in 1922-91 was just a part of it, though obviously the biggest. The terms are not interchangeable. Lenin was head of Russia's government, but also of the USSR's in his last year: the two posts continued to be held by the same person until 1929 but were thereafter separated, the Russian office being of lesser rank.