[kavin011]

Dear All,

     Copper metal reacts with O2 molecule (O2= Covalent bond) and given the products like Cu2O and CuO. Copper valency is 1 and O2 molecule is now stable because of covalent bond(8 sharing electrons). Now how that 1 valency copper atom will react with stable O2 molecule? how chemistry beginners know that what type of chemical reaction will takes place in between these two atoms and why that particular reaction only happened (ex-synthesis)?Please give me a clear explanation step by step to learn the basics in depth. 

[Borek]

It is not like you can expect simple answer - there is a reason why learning chemistry typically takes many years (and even after you get a PhD it will often surprise you).

Copper valency is not just 1, it can be 2 as well. Predicting exact outcome of the reaction is rarely as simple as looking just at the electron configuration, it is quite often a mix of kinetics and thermodynamics.

At high school level it is best to just remember that there are two copper oxides, with CuO being the more stable one.

[Enthalpy]

Nearly all reactants are stable like O₂. This explains why many reactions need some sort of kick, like a flame or a catalyst, to proceed.

Some reactions take place, others don't, and it may depend on the conditions. An approximate condition is if the reaction releases energy, that is, if the formation of the new bonds releases more energy than breaking the old ones consumes. This is the case with CuO, because O₂ isn't very stable.

[kavin011]

Dear All,

     My doubt is Oxygen (O) is available in O2 form in atmosphere,which means it is already stable atom because O (6 valency e-) + O (6 valency e-) sharing their electron to become a covalent  bond (O2).If O2 is stable (Fullfill Octet rule ) than why O2 is participating the chemical reactions? I saw lewis structure of Copper and Oxygen reaction in internet.Copper has valency is +1 & +2 .In lewis structure if copper has 1 valency means 2 copper (Cu) atom will bond with 6 valency oxygen(O) atom to form Cu2O.But my doubt is oxygen already available as O2 (Covalent bond-sharing 8 eelectrons to fullfill octet rule) form,then how oxygen has 6 valency it is 12 valency ?

[chenbeier]

No, Oxygen is [He] 2s²p⁴. Oxygen share two p orbitals with the p-Orbitals of the other oxygen. Each Oxygen get 8 electrons in this case. Also with other atoms like copper. It is similar.

[Corribus]

Stability is not a binary concept. Dioxygen may stable, in that it doesn't spontaneously decompose, but the O=O pi bond is weak because of electron pair repulsion. O sigma bonds tend  to be comparatively low energy.  This makes dioxygen a pretty powerful oxidant.

[Enthalpy]

Atoms or groups of atoms that have still not satisfied all the possible bonds are called radicals. They are so reactive that they combine among themselves or with other molecules very quickly, so that they are extremely rare. NO for instance is an air pollutant whose concentration is few 10^-5. You may also find some in the interplanetary vacuum, where very rare collisions let radicals live longer.

The normal situation is that all atoms have made bonds that satisfy the valence (with the subtlety that some atoms have varied valences). Chemical reactions hence rearrange atoms that are already in molecules (or ions in solvents, and I must forget a few).

Tables with the strength of usual bonds:
http://www.chem.ucalgary.ca/courses/350/Carey5th/useful/bonde.html
https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Bond_Energies
be careful with such tables. They are too inaccurate for many goals. Check if the energy is already doubled in a double bond. The strength of a bond depends much on nearby atoms.