APA (7th ed.) Citation

Penney, W. G. (1935). The quantum theory of valency. Methuen.

Chicago Style (17th ed.) Citation

Penney, William George. The Quantum Theory of Valency. London: Methuen, 1935.

MLA (8th ed.) Citation

Penney, William George. The Quantum Theory of Valency. Methuen, 1935.

Warning: These citations may not always be 100% accurate.