When is an object in stable equilibrium?

Answer 1

Atoms are generally stable if they meet a few conditions:

1. Their valence electron shell is filled. This can occur by ionizing (gaining or losing electrons so that the highest-energy shell is full), or by electron sharing (via an electron 'sea' in metals, or by sharing of pairs of electrons in non-metals). Atoms with partially-full valence shells are chemically unstable, meaning that they react very readily with other elements.
   1. A nucleus with Too few neutrons will tend to capture its electrons or emit positrons (anti-electrons), neutralizing a proton and turning into a different element.
   2. A nucleus with Too many neutrons will tend to emit an electron by beta decay, turning one of its neutrons into a proton and turning into a different element.
   3. Additionally, once atoms reach a certain mass, there is no stable ratio of neutrons to protons, and the nucleus will either eject alpha particles from the nucleus until stable (alpha decay), or it will fission, breaking apart into two or more smaller nuclei.
2. They have a certain ratio of protons and neutrons:

Atoms with unstable proton to neutron ratios are radioactive, meaning they will undergo some type of decay until they reach a form that is stable.

Answer 2

If it has 8 valance electrons (doesn't matter if it got them from another atom or is sharing with another atom).

Answer 3

When we say equilibrium, it is a state of balance. Meaning the summation of all forces in a system is equal to zero and the three states of equilibrium are; stable, unstable and neutral.

Answer 4

When the forces acting on the object are stable