运气 (yùn qi) is a noun meaning 'luck' — it can be good or bad (e.g., 运气好 'good luck', 运气不好 'bad luck'). 好运 (hǎo yùn) means only 'good luck', while 幸运 (xìng yùn) is more often an adjective ('lucky') and less commonly a noun. 福 (fú) and 福气 (fú qi) refer to lasting good fortune or blessings, not chance luck.