Answer:
hope you like it
Explanation:
because ouytermost shell contains two electrons
calcium is in group 2 so its valency is two valency is the number of outer shelll electrons it needs to have an stable outer shell . it needs 2 more .
<u>Mendeleev </u><u>positioned elements in the periodic table in</u><u> increasing order </u><u>of their atomic numbers, such that </u><u>elements </u><u>having identical chemical properties and characteristics plunge into the </u><u>same group.</u>
What is Mendeleev's periodic table called?
- In order to represent similarities and patterns in the behavior of elements, Mendeleev created the periodic table, which is an arrangement of elements in an increasing atomic mass order in tablet form.
- Mendeleev stated that "Element characteristics are a periodic function of their atomic weight" in his renowned periodic law.
- The Periodic Table of Mendeleev is a table that Mendeleev created to list elements in the order of their atomic weights.
- Mendeleev discovered that there were two elements with atomic weights between 65.2 and 75 because he found it very satisfying that the properties of the elements were more similar and closer to this level.
- He also imagined having other elements with possessions similar to those of these other elements.
- In the periodic table, he left a blank for these two elements until they were finally discovered in their true existence.
Learn more about Mendeleev's periodic table
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HBr and HF are both monoprotic Arrhenius acids—that is, in aqueous solution, they dissociate and ionize to give hydrogen ions. A strong acid ionizes completely; a weak acid ionizes partially.
In this case, HBr, being a strong acid, would ionize completely in water to yield H+ and Br- ions. However, HF, being a weak acid, would ionize only to a limited extent: some of the HF molecules will ionize into H+ and F- ions, but most of the HF will remain undissociated.
pH is, by definition, a measurement of the concentration of hydrogen ions in solution (pH = -log[H+]). A higher concentration of hydrogen ions gives a lower pH, while a lower concentration of hydrogen ions gives a higher pH. At 25 °C, a pH of 7 indicates a neutral solution; a pH less than 7 indicates an acidic solution; and a pH greater than 7 indicates a basic solution.
If we have equal concentrations of HBr and HF, then the HBr solution will have a greater concentration of hydrogen ions in solution than the HF solution. Consequently, the pH of the HBr solution will be less than the pH of the HF solution.
Choice A is incorrect: Strong acids like HBr dissociate completely, not partially.
Choice B is incorrect: While the initial concentration of HBr and HF are the same, the H+ concentration in the HBr solution is greater. Since pH is a function of H+ concentration, the pH of the two solutions cannot be the same.
Choice C is correct: A greater H+ concentration gives a lower pH value. The HBr solution has the greater H+ concentration. Thus, the pH of the HBr solution would be less than that of the HF solution.
Choice D is incorrect for the reason why choice C is correct.
C, that cells cannot be created nor destroyed.
Cells are produce by other cells. Cells can not be man-made nor destroyed.
