Mendeleev's periodic table
Dmitri Mendeleev
Like many scientists working at the end of the 19th-century the Russian chemist Dmitri Mendeleev (1834-1907) was looking for ways to organise the known elements. Mendeleev published his first periodic table of the elements in 1869.
Features of Mendeleev's tables
Mendeleev arranged the elements in order of increasing relative atomic mass. When he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend. He then arranged the elements by putting those with similar properties below each other into groups. To make his classification work Mendeleev made a few changes to his order:
he left gaps for yet to be discovered elements
he switched the order of a few elements to keep the groups consistent
The differences are <u>the number of neutrons</u> and the <u>atomic mass</u><u /><u />.
Copper-63 has an atomic mass of 63 amu, and has 34 neutrons.
Copper-65 has an atomic mass of 65 amu, and has 36 neutrons.
Answer:
- <u><em>Option D. There will be a shift toward the reactants.</em></u>
Explanation:
The reaction is:

The application of LeChatelier's principle leads to consider the <em>heat</em> as a <em>reactant</em> or a product depending on if it is on the left side or the right side.
In this reaction, the <em>heat</em> is on the left side, thus it must be considered a <em>reactant</em>.
Decreasing the temperature is equivalent to remove or consume heat. Thus, the reaction must shif to the left to compensate that reduction of heat. That is the reverse reaction shall be favored.
In conclusion, <em>there will be a shift toward the reactants.</em>
<u>Answer: </u>The concentration of
in the solution is 
<u>Explanation:</u>
pH is defined as the negative logarithm of hydrogen ion concentration present in the solution.
.....(1)
We are given:
pH of solution = 2.5
Putting values in equation 1, we get:
![2.5=-\log [H^+]](https://tex.z-dn.net/?f=2.5%3D-%5Clog%20%5BH%5E%2B%5D)
![[H^+]=10^{-2.5}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D10%5E%7B-2.5%7D)
![[H^+]=3.16\times 10^{-3}M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D3.16%5Ctimes%2010%5E%7B-3%7DM)
Hence, the concentration of
in the solution is 
Answer:
5 million million atoms can fit at the end of a needle