Toss the beef with 1/2 teaspoon each salt and pepper. Heat the oil in a pressure cooker over medium-high heat. Add the beef and cook, stirring occasionally, until browned on all sides, about 4 minutes.Add the onions and cook, stirring frequently, until the onions soften and begin to brown, about 4 minutes.eat the oil in a pressure cooker over medium-high heat. Add the beef and cook, stirring occasionally, until browned on all sides, about 4 minutes. Add the onions and cook, stirring frequently, until the onions soften and begin to brown, about 4 minutes.
Thus, metals have positive electron affinities. In the Periodic Table, electron affinity increases (becomes more negative) from left to right in a period. Electron affinity decreases from top to bottom in a Group.
Nonmetals also have high electron affinity. This means that it is energetically favorable to add an electron to a nonmetal. So, nonmetals can be easily reduced. Metals tend to have low electron affinity so it is more difficult to add electrons (or reduce them). In short: Metals have low ionization energies and low electron affinities so they are readily oxidized. Nonmetals have high ionization energies and high electron affinities so they are readily reduced.