The positive particle in the nucleus that attracts electrons would be the protons.
Atoms are composed of three type of particles: protons, neutrons, and electron. Protons and neutrons are responsible for most of the atomic mass. The mass of an electron is very small (9.108 X 10-28 grams).
Both the protons and neutrons reside in the nucleus. Protons have a postive (+) charge, neutrons have no charge --they are neutral. Electrons reside in orbitals around the nucleus. They have a negative charge (-).
It is the number of protons that determines the atomic number, but neutron number may vary, so mass number (protons + neutrons) may vary.
You can learn more about atomic structure at the following sites:
New York University
BBC
Encyclopedia.com