The number of electrons in it's valance shell.
The electron configuration of an atom determines how it behaves when it comes into contact with another atom.
The number of protons in the nucleus of an atom distinguishes it from another atom. This number is known as the atomic number and determines the element to which the atom belongs.
The particle of an atom that determines how it will bond with another atom is the electron, specifically the valence electrons. These are the electrons in the outermost shell of an atom and are responsible for chemical bonding. Atoms can share, gain, or lose valence electrons to achieve a stable electron configuration, leading to the formation of covalent, ionic, or metallic bonds.
the number of protons in an atom is what determines which element the atom is. So if an atom "lost" a proton, it would become another element entirely.
The atomic number, which is the number of protons in the nucleus, determines what kind of atom it is.
The Valence Electron structure of the two atoms and, the Temperature, Pressure and Concentration (proximity) of the two atoms.
Neutron
the number of protons determines the atom.
Nonpolar Covalent Bond
angles
Mass Number
i am pretty sure that it is the mass and temperature of the atom