Atomic Structure
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Each atom of the a specific element has a constant and unique number of protons. Each element of an atom has an equal number of protons and electrons. Therefore, the element and its physical properties are defined by the number of protons and electrons specific to the element.
Atomic Number of an element is referred to as Z and is the total number of protons (P+) that the element has. Since each element has the same number of electrons as protons the Atomic Number is also equal to the number of electrons each element has.
Atomic Mass of an element is the total mass (weight) of all the protons, neutrons and electrons that make up the atom of an element. The protons and neutrons are much bigger and heavier than the electrons. The protons and neutrons have an individual Atomic Mass of about 1.
Given the information in the above paragraph, we can calculate the
number of neutrons in an element from the Atomic Mass and the Atomic
Number. Since the Atomic Mass rounded to the nearest whole number is equal to
the sum of the number of protons and neutrons, and the Atomic Number
is the number of protons, then the # Neutrons can be calculated as follows:
# Neutrons (N) = Atomic Mass - Atomic Number (Z)
Building the Elements
Hydrogen As stated above each element is made up of an unique and
equal number of protons and electrons. The simplest element is Hydrogen,
the most abundant element on earth. The Atomic Structure of Hydrogen has one proton and one
electron and therefore, it has an Atomic Number of 1.
Some of the most common elements and their number of protons and electrons are show in the table above.
Helium If we add one additional proton and one additional electron to Hydrogen, we have the element Helium, the second most abundant element on earth. Helium is the gas that is used to inflate balloons for kids' parties. Since Helium has two protons it has an Atomic Number of 2.
Carbon If we continue adding protons and electrons until we have a total of six each, we have the element carbon which has a Atomic Number of 6. Carbon is the fourth most abundant element on earth and is present in all known lifeforms.
Nitrogen If one more proton and electron are added to carbon we have the element Nitrogen with a total of seven protons and electrons and an Atomic Number of 7. Nitrogen is a very common element in nature. Air is approximately 80% nitrogen.
Oxygen Adding one more proton and electron to Nitrogen gives us the element Oxygen which has a total of 8 protons and electrons and an Atomic Number of 8. Air is approximately 20% oxygen and is necessary for all human life.
The proton and electron composition of all 103 known elements can be constructed in this manner, beginning with Hydrogen and adding one proton and one electron at a time. The first 12 elements are shown in the table above.
Electron Orbitals-Energy Levels-Shells-Subshells
Electrons As we discussed in the first section above, the atomic structure of an atom is like a our solar system with protons and
neutrons in the nucleus at the center of the atom, and electrons
orbiting around the nucleus like our planets orbit around the sun.
Electrons (- charged) are held in their orbit around the nucleus by
electrostatic attraction to the protons (+ charged) in the nucleus.
Just as the planets have different orbits, the electrons, as we add them to form the various elements, have different orbits. Electrons occupy different orbits based on the energy level of the orbits with the lower energy level orbits being filled with electrons first.
Quantum Levels = Shells Each of the energy levels, sometimes referred to as Quantum Levels, are more commonly called "Shells". Each shell is made up of four different energy levels called "Subshells".
Subshells = OrbitalsEach Sub-Shell has a different shape as shown in the two pictures to the left. The picture above is a table of the different electron orbitals and the picture below is a graphical representation of the sub-shell shapes.
The lowest energy level for electrons has a spherical shape and is referred to as an s-subshell. There is only one s-subshell per Quantum Level (Shell) and each s-subshell only has one spherical orbital with room for two electrons.
The next highest energy levels that electrons can orbit in once the s- subshell is filled is called the p-subshell and contains three dumbell- shaped orbitals each of which can hold two orbitals for a total of 6 electrons to fill up the p-subshell.
As we build different elements by adding protons and electrons, the electrons first two go into the s-orbital. The third through the eighth electrons go into the three p-orbitals.
We will in more detail at how the elements are built up and where the electrons go in the following sections.
Building the Hydrogen (H) Atom
The picture above represents the Atomic Structure of the Hydrogen Atom. The nucleus is
not shown as we are now just interested in what orbitals the electrons
occupy as we add them to form different elements. The different Shells,
Subshells and their orbitals are represented by different colored
rectangles at the left of the picture with increasing energy levels
from bottom to top.
As we have discussed above, Hydrogen is the simplest element and is made of one proton and one electron which occupies the s-orbital of the first shell represented in the picture above as yellow. Shell #1 is small and only has one s-orbital and no p-orbitals.
Hydrogen has one proton and one electron which gives it an Atomic Number (Z) of 1.
Building the Helium (He) Atom
If we add one proton and one electron to Atomic Structure of Hydrogen we get an atom of the
element Helium.
Since there is room for a total of two electrons in each orbital the added electron that makes Hydrogen into Helium goes into the s-orbital of the first Shell (Shell #1) as shown in the picture above. The resulting Helium Atom has a full first Shell (Shell #1).
Helium has two protons and two electrons which gives it an Atomic Number (Z) of 2.
Building the Lithium (Li) Atom
If we add one proton and one electron to the Atomic Structure of Helium we get an atom of the
element Lithium. For Helium, the first shell (Shell #1) is full. So the added electron
that makes Helium into Lithium must go into the lowest energy orbital,
the s- orbital, of the second Shell (Shell #2) as shown in green in the
picture above.
Lithium has three protons and three electrons which gives it an Atomic Number (Z) of 3.
Building the Beryllium (Be) Atom
If we add one proton and one electron to the Atomic Structure of Lithium we get an atom of the
element Beryllium.
For Lithium, the s-orbital in Shell #1 is full and there is one electron in s-orbital of Shell #2. So the added electron that makes Lithium into Beryllium will go to fill the the s-orbital of the second Shell (Shell #2) as shown in the picture above.
Beryllium has four protons and four electrons which gives it an Atomic Number (Z) of 4.
Building the Boron (B) Atom
If we add one proton and one electron to the Atomic Structure of Beryllium we get an atom of the
element Boron.
For Beryllium the s-orbital of Shell #2 is full. So the added electron that makes Beryllium into Boron must go into the first p-orbital of the second Shell (Shell #2) as shown in the picture above.
Boron has five protons and five electrons which gives it an Atomic Number (Z) of 5.
Building the Carbon (C) Atom
If we add one proton and one electron to the Atomic Structure of Boron we get an atom of the element Carbon.
For Boron the s-orbital of Shell #2 is now full. However, there is only one electron in the first p-orbital of Shell #2, so the added electron that makes Boron into Carbon will go into the second p-orbital of the second Shell (Shell #2) as shown in the picture above.
Carbon has six protons and six electrons which gives it an Atomic Number (Z) of 6.
Building the Nitrogen (N) Atom
If we add one proton and one electron to the Atomic Structure of Carbon we get an atom of the element Nitrogen.
For Carbon the s-orbital of Shell #2 is full and there are two electrons in the p- orbitals of Shell #2, so the added electron that makes Carbon into Nitrogen will go into the third p-orbital of the second Shell (Shell #2) as shown in the picture to the left.
Nitrogen has seven protons and seven electrons which gives it an Atomic Number (Z) of 7.
Building the Oxygen (O) Atom
If we add one proton and one electron to Nitrogen we get an atom of the element Oxygen.
For Nitrogen the s-orbital of Shell #2 is full, but there are still only three electrons in the p-orbitals of Shell #2. (Remember each of the three p-orbitals can hold two electrons for a total of 6). So the added electron that makes Nitrogen into Oxygen will fill one of the three p- orbitals of the second Shell (Shell #2) as shown in the picture above.
Oxygen has eight protons and eight electrons which gives it an Atomic Number (Z) of 8.
Building the Fluorine (F) Atom
If we add one proton and one electron to the Atomic Structure of Oxygen we get an atom of the element Fluorine.
For Oxygen the s-orbital of Shell #2 and one of the three p-orbitals of Shell #2 are full. So the added electron that makes Oxygen into Fluorine will go to fill the second p-orbital of the second Shell (Shell #2) as shown in the picture above.
Fluorine has nine protons and nine electrons which gives it an Atomic Number (Z) of 9.
Building the Neon (Ne) Atom
If we add one proton and one electron to Fluorine we get an atom of the element Neon.
For Fluorine the s-orbital of Shell #2 and two of the three p-orbitals of Shell #2 are full. So the added electron that makes Fluorine into Neon will go to fill the third of three p-orbitals of the second Shell (Shell #2) resulting in a completely full Shell #2 as shown in the picture above.
Neon has 10 protons and 10 electrons which gives it an Atomic Number (Z) of 10.
Building the Sodium (Na) Atom
If we add one proton and one electron to the Atomic Structure of Neon we get an atom of the element Sodium.
For Neon the entire Shell #2 us full so the added electron that makes Neon into Sodium will have to go into the lowest energy orbital, the s- orbital, of the third Shell (Shell #3) as shown in blue in the picture above.
Sodium has 11 protons and 11 electrons which gives it an Atomic Number (Z) of 11.
Building the Magnesium (Mg) Atom
If we add one proton and one electron to Sodium we get an atom of the element Magnesium.
For Sodium both Shell #1 and Shell #2 are full and there is one electron in the s-orbital of Shell #3. So the added electron that makes Sodium into Magnesium becomes the second electron to occupy the s- orbital of the third Shell (Shell #3) giving a full s-orbital of Shell #3 as shown in the picture above.
Magnesium has 12 protons and 12 electrons which gives it an Atomic Number (Z) of 12.
Building the Aluminum (Al) Atom
If we add one proton and one electron to Atomic Structure of Magnesium we get an atom of the element Aluminum.
For Magnesium both Shell #1 and Shell #2 are full and there are now two electrons in the s-orbital of Shell #3 so that orbital is full. So the added electron that makes Magnesium into Aluminum will become the first electron to occupy one of the three p-orbitals of the third Shell (Shell #3) as shown in the picture above.
Aluminum has 13 protons and 13 electrons which gives it an Atomic Number (Z) of 13.
Building the Silicon (Si) Atom
If we add one proton and one electron to Aluminum we get an atom of the element Silicon.
For Aluminum Shell #1, Shell #2 and s-orbital of Shell #3 are full. There is also one electron in the first p-orbital of Shell #3. So the added electron that makes Magnesium into Aluminum will occupy the third of the three p-orbitals of the third Shell (Shell #3) as shown in the picture above.
Silicon has 14 protons and 14 electrons which gives it an Atomic Number (Z) of 14.
Building the Phosphorous (P) Atom
If we add one proton and one electron to the Atomic Structure of Silicon we get an atom of the element Phosphorous.
For Silicon both Shell #1, Shell #2 and the s-orbital of Shell #3 are full. The p-orbitals of Shell #3 contain 2 electrons. The added electron that makes Silicon into Phosphorous will occupy the third p- orbital of the third Shell (Shell #3) as shown in the picture above.
Phosphorous has 15 protons and 15 electrons which gives it an Atomic Number (Z) of 15.
Building the Sulfur (S) Atom
If we add one proton and one electron to Phosphorous we get an atom of the element Sulfur.
For Phosphorous both Shell #1, Shell #2 and the s-orbital of Shell #3 are full. The each of the three p-orbitals of Shell #3 contains one electron for a total of 3 in the p-orbitals of Shell #3. The added electron that makes Phosphorous into Sulfur will fill the first p- orbital of the third Shell (Shell #3) as shown in the picture above.
Sulfur has 16 protons and 16 electrons which gives it an Atomic Number (Z) of 16.
Building the Chlorine (Cl) Atom
If we add one proton and one electron to the Atomic Structure of Sulfur we get an atom of the element Chlorine.
For Sulfur both Shell #1, Shell #2 and the s-orbital of Shell #3 are full. The first p-orbital of Shell #3 is full with two electrons and each of the other two p-orbitals of Shell #3 contains one electron for a total of 4 in the p-orbitals of Shell #3. The added electron that makes Sulfur into Chlorine will fill the second p-orbital of the third Shell (Shell #3) as shown in the picture above.
Chlorine has 17 protons and 17 electrons which gives it an Atomic Number (Z) of 17.
Building the Argon (Ar) Atom
If we add one proton and one electron to Chlorine we get an atom of the element Argon.
For Argon both Shell #1, Shell #2 and the s-orbital of Shell #3 are full. The first two p-orbitals of Shell #3 are full with two electrons and each of the other p-orbital of Shell #3 contains one electron for a total of 5 in the p-orbitals of Shell #3. The added electron that makes Chlorine into Argon will fill the third p-orbital of the third Shell (Shell #3) leading to a completely full Shell #3 as shown in the picture above.
Argon has 18 protons and 18 electrons which gives it an Atomic Number (Z) of 18.
Building the Potassium (K) Atom
If we add one proton and one electron to the Atomic Structure of Argon we get an atom of the element Potassium.
For Potassium Shell #1, Shell #2 and Shell #3 are full. So the added electron that makes Argon into Potassium will go into the lowest energy orbital of Shell #4, the s-orbital as shown in the picture above.
Potassium has 19 protons and 19 electrons which gives it an Atomic Number (Z) of 19.
Building the Calcium (Ca) Atom
If we add one proton and one electron to Potassium we get an atom of the element Calcium.
For Calcium Shell #1, Shell #2 and Shell #3 are full and the s-orbital of Shell #4 has one electron. So the added electron that makes Potassium into Calcium will go to fill the s-orbital of Shell #4 as shown in the picture above.
Calcium has 20 protons and 20 electrons which gives it an Atomic Number (Z) of 20.
Grouping Elements by Atomic Structure
In the above discussion we have step-by-step, proton and electron by
proton and electron, build the first 20 elements from the simplest
Hydrogen (H). We could continue this process for the remaining of the
103 known elements but we won't.
By now you should have a good understanding of the specific and unique Atomic Structure of the atoms of each element. These elements can be grouped by Atomic Structure as shown in the picture above.
In the two tables above we list the 20 elements we have constructed in order of increasing Atomic Number. This means of course in the order of increasing number of protons.
We have also included the Shells labeled by number and color coded to match our atom structure diagrams. In addition we have listed the Atomic Mass and a column in which we calculated the number of neutrons as described above.
This completes our tutorial on the Atomic Structure of matter and lays a solid foundation for understanding the grouping of elements by Atomic Structure which is the basis for the Periodic Table.
Now, that you have learned about Atomic Structure you are ready to group the Elements by their Atomic
Structure. This is the basis for the Periodic Table.
Click here for a tutorial on the Periodic Table.
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