I was reminded of this article by Michelle Francl[1], where she poses the question “What anchor values would most benefit students as they seek to hone their chemical intuition?” She gives as common examples: room temperature is 298.17K (actually 300K, but perhaps her climate is warmer than that of the UK!), the length of a carbon-carbon single bond, the atomic masses of the more common elements.
References
- M. Francl, "Take a number", Nature Chemistry, vol. 5, pp. 725-726, 2013. http://dx.doi.org/10.1038/nchem.1733