The Lactose molecule in 3-D

The Lactose molecule - rotatable in 3 dimensions

Lactose (milk sugar) is a disaccharide - formula C12H22O11 - consisting of one galactose unit and one glucose unit, combined.

The two sugars are linked via a glycosidic bond - a beta 1-4 bond between galactose and glucose.

This bond - effectively an oxygen bridge - is formed as a result of a condensation reaction.

Label / unlabel bonding carbon atom numbers.

Note that one of these ring-shaped sections (glucose) is in equilibrium with an open-chain form in which Carbon 1 has a CHO aldehyde group which gives it reducing properties, so that it reacts with reagents such as Benedict's.
Label/ Unlabel atoms

Possibly relevant
material available online
(from Amazon.com)

Possibly relevant
material available online
(from Amazon.co.uk)