What is the difference...?

Question

between an atom of oxygen, a molecule of oxygen and an ion of oxygen (oxide ion)?

Please help me.

Also,

question 2:
When the calcium atom forms its own ion
a) the mass number is unchanged
b) it gains two electrons
c) it loses two neutrons
d) it achieves the elctron configuration of neon
e) it loses two protons

Multiple choice...choice the ONE correct answer. Thankyou

Answer 1

An atom of oxygen is a single, smallest unit consisting of a nucleus containing 16 protons. A molecule of oxygen is two atoms of oxygen sharing an electron cloud. It is expressed as O2.
Atomic oxygen is unstable and doesn't exist naturally. Molecular oxygen is what we breathe.
An ion of oxygen, oxide, is oxygen atom which picks up two electrons. It is expressed as O2-.

For the calcium ion question, the correct answer is a. The mass number is unchanged.
Ions are formed by an atom (or functional group) gaining or losing electrons only. Since atomic mass is calculated only by adding the protons and neutrons (electrons are considered to have no mass), the number is unchanged.
b is incorrect since Ca2+ gives up two electrons, not gains two.
c is incorrect since gaining or losing neutrons forms an isotope.
d is incorrect since, as an ion, Calcium (Ca2+) has the configuration of Argon (Count back two spaces on the periodic table).
e is incorrect, since the number of protons determines the element. This process is called transmutation, the goal of alchemy. Early alchemists sought to turn lead and other metals into gold.