•common trends and similarities
•similar ions going down (ex: Mg+2 and Ca+2)
•same number of electron orbitals going across
In 250 mL of volumetric flask add 0.975875 grams of 
and dissolve it in the 250 mL of water.
Given:
The solid of calcium fluoride.
To prepare:
The 250 mL solution of 0.100 M of fluoride ions from solid calcium fluoride.
Method:
Molarity of the fluoride ion solution needed = M = 0.100 M
The volume of the fluoride ion solution needed = V = 250 mL
The moles of fluoride ion needed = n
According to the definition of molarity:
Moles of fluoride ion = 0.025 mol
We know that solid calcium fluoride dissolves in water to give calcium ions and fluoride ions.
According to reaction, 2 moles of fluoride ions are obtained from 1 mole of calcium fluoride, then 0.025 moles of fluoride ions will be obtained from:
Moles of calcium fluoride = 0.0125 mol
Mass of calcium fluoride needed to prepare the solution :
Preparation:
- Weight 0.975875 grams of calcium fluoride
- Add weighed calcium fluoride to a volumetric flask of the labeled volume of 250 mL.
- Now add a small amount of water to dissolve the calcium fluoride completely.
- After this add more water up to the mark of the volumetric flask of volume 250 mL.
Learn more about molarity of solution ere:
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Answer:
electrons should be added to one of these spheres to make it electrically neutral.
Explanation:
Total charge on each sphere = +3.0 μC =
In order to neutralize the positive charge equal magnitude of negative charge is to be added.
Total charge electrons, Q= -3.0 μC =
Number of electrons = n
Charge on a single electron, e = 
Q = n × e
electrons should be added to one of these spheres to make it electrically neutral.
Answer: "The reactants are higher in energy than the products"
Explanation:
The exothermic reactions are characterized by the release of heat to the surroundings. The reactants lose heat that is delivered to the surroundings which implies that the products will be lower in energy than the reactants.
The hills that you can see in a reaction energy diagram are not related with the final change of energy. The hills are an indication of the activation energy needed to start the reaction, but they do not measure the change of energy from the products to the reactants.
The enthalpy that is a state variable that identifies the content of heat. Then the change of enthalpy for the exothermic reactions is negative, meaning that the energy of the products is lower than the energy of the reactants.
Answer:
Aluminium.
Explanation:
The above electronic configuration can be written in a simplified form as shown below:
1s² 2s²2p⁶ 3s²3p¹
Next, we shall determine the number of electrons in the atom of the element as follow:
Number electron = 2 + 2 + 6 + 2 + 1
Number of electron = 13
Next, we shall determine the number of protons.
Since the element is in its neutral state,
The number of electrons and protons are equal i.e
Proton = Electron
Number of electron = 13
Proton = Electron = 13
Proton = 13
Next, we shall determine the atomic number of the element.
The atomic number of an element is simply the number of protons in the atom of the element i.e
Atomic number = proton number
Proton = 13
Atomic number = 13
Comparing the atomic number of the element with those in the periodic table, the element with the above electronic configuration is aluminium since no two elements have the same atomic number.
