  The Atacama Large Millimeter/submillimeter Array (ALMA) allows for solar
observations in the wavelength range of 0.3$-$10 mm, giving us a new view of
the chromosphere. The measured brightness temperature at various frequencies
can be fitted with theoretical models of density and temperature versus height.
We use the available ALMA and Mets\"ahovi measurements of selected solar
structures (quiet sun (QS), active regions (AR) devoid of sunspots, and coronal
holes (CH)). The measured QS brightness temperature in the ALMA wavelength
range agrees well with the predictions of the semiempirical
Avrett$-$Tian$-$Landi$-$Curdt$-$W\"ulser (ATLCW) model, better than previous
models such as the Avrett$-$Loeser (AL) or Fontenla$-$Avrett$-$Loeser model
(FAL). We scaled the ATLCW model in density and temperature to fit the
observations of the other structures. For ARs, the fitted models require
9%$-$13% higher electron densities and 9%$-$10% higher electron temperatures,
consistent with expectations. The CH fitted models require electron densities
2%$-$40% lower than the QS level, while the predicted electron temperatures,
although somewhat lower, do not deviate significantly from the QS model.
Despite the limitations of the one-dimensional ATLCW model, we confirm that
this model and its appropriate adaptations are sufficient for describing the
basic physical properties of the solar structures.
