How does the number of valence electrons change across a periodic table?
In general, each group or family of the periodic table is a column. The first 2 columns and the last 6 columns are called the representative elements. The first column has 1 valence, the second column has 2 valence, the 3A or group 13 column has 3 valence, 4A or group 14 has 4 valence, .... up to group 8A or column 18 has 8 valence (Noble gases).
For the representative groups the valence electrons increase across the periodic table.
The transition metals (B group) found in columns 3-12 have either 1 or 2 valence electrons.