Electrons in an atom can be classified as core electrons and valence electrons. Valence electrons are those electrons which are present in valence shell and participates in bond formation. While, Core electrons are all remaining electrons which are not present in valence shell, hence not take part in bonding.
Atomic number of Selenium (Se) is 34 hence it has 34 electrons with following electronic configuration;
1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁴
From electronic configuration it is found that the valence shell is 4, and the number of electrons present in valence shell are 6. So,
Core Electrons = Total Electrons - Valence Electrons
Core Electrons = 34 - 6
Core Electrons = 28
Result:
There are 28 core electrons in Selenium.
Answer:
Explanation:
To answer this question successfully, we need to remember that atoms are neutral species, since the number of protons, the positively charged particles, is equal to the number of electrons, the negatively charged particles. That said, we may firstly find an atom which has 3 electrons (and, as a result, 3 protons, as it should be neutral).
The number of protons is equal to the atomic number of an element. We firstly may have an atom with 3 protons and 3 electrons (atomic number of 3, this is Li).
Similarly, we may take the atomic number of 4, beryllium, and remove 1 electron from it. Upon removing an electron, it would become beryllium cation, 
.
We may use the same logic going forward and taking the atomic number of 5. This is boron. In this case, we need to remove 2 electrons to have a total of 3 electrons. Removal of 2 electrons would yield a +2-charged cation: 
.
Answer:
D. A compound can be separated into two or more elements through a chemical reaction.
Explanation:
By method of elimination, we are going t obtain the correct option.
A. A compound is made up of a single atom.
This is wrong because, a compound can contain more than one atom. An example is H2O
B. A compound is made up of many atoms that are all the same type.
This is wrong because a compound can contain atoms of different elements. An example is H2O. It contains atoms of hydrogen and oxygen.
C. A compound can be separated into two or more elements through physical processes.
This is wrong. H2O being a compound cannot be separated by ordinary physical means.
D. A compound can be separated into two or more elements through a chemical reaction.
This is the correct option.
If the ion is negatively charged, anion, it means that it gains two
electrons from its surroundings. The number of electrons of an argon (neutral
atom) is 18. Two of the electrons in our anion is from the surrounding, so
originally it only has 16 electrons.
In the periodic table, the 16th element is sulphur. The
chemical symbol of sulphur is S. Thus, the anion is the negatively charged
sulphur with chemical symbol of S2-.
Answer:
Rate constant k = 1.57*10⁻⁵ s⁻¹
Explanation:
Given reaction:
Expt [A] M [B] M Rate [M/s]
1 3.40 4.16 1.82*10^-4
2 4.59 4.16 3.32*10^-4
3. 3.40 5.46 1.82*10^-4
![Rate = k[A]^{x}[B]^{y}](https://tex.z-dn.net/?f=Rate%20%3D%20k%5BA%5D%5E%7Bx%7D%5BB%5D%5E%7By%7D)
where k = rate constant
x and y are the orders wrt to A and B
To find x:
Divide rate of expt 2 by expt 1
![\frac{3.32*10^{-4} }{1.82*10^{-4} } =\frac{[4.59]^{x} [4.16]^{y} }{[3.40]^{x} [4.16]^{y} }\\\\x =2](https://tex.z-dn.net/?f=%5Cfrac%7B3.32%2A10%5E%7B-4%7D%20%7D%7B1.82%2A10%5E%7B-4%7D%20%7D%20%3D%5Cfrac%7B%5B4.59%5D%5E%7Bx%7D%20%5B4.16%5D%5E%7By%7D%20%7D%7B%5B3.40%5D%5E%7Bx%7D%20%5B4.16%5D%5E%7By%7D%20%7D%5C%5C%5C%5Cx%20%3D2)
To find y:
Divide rate of expt 3 by expt 1
![\frac{1.82*10^{-4} }{1.82*10^{-4} } =\frac{[3.40]^{x} [5.46]^{y} }{[3.40]^{x} [4.16]^{y} }\\\\y =0](https://tex.z-dn.net/?f=%5Cfrac%7B1.82%2A10%5E%7B-4%7D%20%7D%7B1.82%2A10%5E%7B-4%7D%20%7D%20%3D%5Cfrac%7B%5B3.40%5D%5E%7Bx%7D%20%5B5.46%5D%5E%7By%7D%20%7D%7B%5B3.40%5D%5E%7Bx%7D%20%5B4.16%5D%5E%7By%7D%20%7D%5C%5C%5C%5Cy%20%3D0)
Therefore: x = 2, y = 0
![Rate = k[A]^{2}[B]^{0}](https://tex.z-dn.net/?f=Rate%20%3D%20k%5BA%5D%5E%7B2%7D%5BB%5D%5E%7B0%7D)
To find k
Use rate for expt 1:
![k = \frac{Rate1}{[A]^{2} } =\frac{1.82*10^{-4}M/s }{[3.40]^{2} } =1.57*10^{-5} s-1](https://tex.z-dn.net/?f=k%20%3D%20%5Cfrac%7BRate1%7D%7B%5BA%5D%5E%7B2%7D%20%7D%20%3D%5Cfrac%7B1.82%2A10%5E%7B-4%7DM%2Fs%20%7D%7B%5B3.40%5D%5E%7B2%7D%20%7D%20%3D1.57%2A10%5E%7B-5%7D%20s-1)
