Periodic table is the representation of elements in an order
The history of periodic table can be summarized as
a) 1829 : Johann Dobereiner proposed the triad rule. According to him we can classify the elements in a triad where the atomic mass of middle element is average of atomic mass of the near by two atoms.
For example : Li, Na and K is a triad. Where atomic mass of Na is average of atomic mass of K
atomic mass of Na = 7+ 39 / 2 = 23
However, with the further discovery of elements the law was rejected.
b) 1864 : John Newland proposed the law of octave. According to him we can arrange the elements in a set of seven elements where the property of second set of seven elements will resemble the properties of first of seven elements or property will be repeated after seven elements. This was also rejected due to its limited applicability.
c) Meyer : He arranged some 28 elements into six different families based on their atomic masses. The members of each familiy shared some common properties.
d) 1869 : Mendleev : He actually developed a periodic table based on atomic mass of elements. He arranged the elements into groups and periods. He even left space for some undiscovered elements, which were later on discovered.
e) 1916 : Henry Moseley : He finally arranged elements based on their atomic number based on X-ray studies. He proposed the modern periodic law that the periodic properties of elements are due to atomic number of elements.
Answer:
Ld₂Mz
General Formulas and Concepts:
<u>Chemistry - Compounds</u>
- Valence shells
- Writing chemical compounds
- Balancing charges
Explanation:
<u>Step 1: Define</u>
"Lindenium" Ld w/ oxidation charge of +1
"Mendezine" Mz w/ oxidation charge of -2
<u>Step 2: Write Compound</u>
To balance out the charges to be neutral (0), we must counter balance the amount of Ld's with Mz's. We need 2 Ld's with 1 Mz to create a compound with a neutral charge:
2Ld¹⁺ + Mz²⁻
2(+1) + (-2) = (+2) + (-2) = 0 (neutral charge)
Therefore, our compound must be Ld₂Mz.
Answer:
What is this? I am confused.
Explanation:
The given question is incomplete. The complete question is:
Consider the spontaneous dissolution of NaCl in water: NaCl(s) → Na+(aq) + Cl −(aq) Predict whether the entropy change for this process is positive or negative and explain your answer. Then, predict whether the free energy change for the process is positive or negative and explain your answer.
Answer: The entropy change is positive. The free energy change for the process is negative and reaction is spontaneous.
Explanation:
Entropy is defined as the degree of randomness of a system. For a system in which randomness increses , the enetropy is said to increase and 
is positive.
As in the given reaction : 
, the solid is dissociating to give ions , randomness increases and thus entropy is positive.
Also the dissociation of a molecule requires energy , thus the enthalpy 
is also positive as heat is absorbed by the system.
when Temperature is high.
A chemical reaction between the metals and the electrolyte frees more electrons in one metal than it does in the other. The metal that frees more electrons develops a positive charge, and the other metal develops a negative charge.
