Gretchen, there is a bus from the Venezia-Marco Polo airport to Padova. Here's some info from www.couchsurfing.com.
When exiting from the Arrivals, continue crossing the first lane. On the second one, search the exact stop turning on your right, the Padova stop is the last one at the right. Buy a ticket at the automatic machine as it costs 3,60€ instead of 5,00€ on the bus. You can select the ticket for Padova selecting other destinations in the menu.
There is a bus every 30 minutes on peak hours and one every hour in off-peak and it takes about 1 hour 10 minutes to get to Padova bus station (Autostazione – Piazzale Boschetti). You will arrive in Padova Bus station, from there you reach the railway station with buses number 9, 7, 19, 24 and then follow to your final destination (for the centre take the Tramway) or just reach by foot Corso Garibaldi crossing the Arena Gardens and from there you will find other bus routes.