Introduction to the Atom (English)

[Music] if everything in the known universe is composed of atoms then we should all have a basic understanding of the atom and the three fundamental subatomic particles the proton the neutron and the electron therefore the goal of this chapter is to define and deduce the number of protons neutrons and electrons that an atom possesses and understand where these subatomic particles reside within an atom there is a great deal of information that can be gleaned from the periodic table in fact many refer to the periodic table as the world's greatest cheat sheet for example what makes helium different from all the other elements found within the periodic table examining helium closer we see that the atomic number for helium is 2 the atomic number indicates how many protons are found in the nucleus of an atom thus elemental identity comes from the number of protons in other words for helium to be helium and must possess only 2 protons if helium gained a proton the atomic number would become 3 which means it's elemental identity would also change from helium to lithium the two protons of helium exists at the center of the atom called the nucleus and each proton has a positive charge the two similar positive charges should repel each other what an attractive force called a strong nuclear force helps to overcome this repulsion and the two subatomic particles are actually attracted to each other it should be noted that this attraction only occurs at the subatomic level the repulsions are further reduced with the help of neutrons the neutrons are also found inside the nucleus which are slightly heavier than the protons and have no charge it may help to think of a neutron as nuclear glue that increases the extent of the strong nuclear force which helps hold the protons together the sum of the protons and neutrons is referred to as the mass number in this example helium has two protons and two neutrons thus the mass number is four which is often given in the upper left-hand corner of the element and the atomic number is two which appears in the lower left-hand corner however the atomic number is often omitted after all atomic number can be deduced from the periodic table if the elemental symbol is given for example the atomic number in the lower left-hand corner does not have to be included for carbon if we have access to a periodic table from the periodic table we see that carbon has an atomic number of six thus there are six protons present to deduce the number of neutrons we simply subtract the number of protons from the mass number thus there are six neutrons remember the mass number is the sum of the neutrons and the protons at this point we can introduce isotopes isotopes are atoms with the same number of protons but different number of neutrons for example the two common isotopes of carbon are carbon-12 and carbon-13 they both have the same number of protons six but the number of neutrons are different carbon-12 has six and carbon-13 has seven neutrons which were deduced from subtracting the number of protons from the mass number now let's look at two isotopes of chlorine and deduce their numbers of protons and neutrons here again the atomic number in the lower left-hand corner has been omitted because we have access to a periodic table examining the periodic table we see that chlorine is atomic number 17 thus both isotopes have 17 protons the mass numbers 35 and 37 then allow us to deduce the number of neutrons for each isotope 18 and 20 the fractional abundance of the chlorine 35 isotope is seventy five point five three percent and the fractional abundance of the chlorine 37 isotope is twenty four point four seven percent put another way in any sample of pure chlorine seventy five point five three percent of the sample is the chlorine 35 isotope and twenty four point four seven percent is the chlorine 37 isotope now let's use this data to introduce the atomic mass of an element the atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes but what are the masses of each isotope and how are they calculated to answer this question we need to introduce the atomic mass unit or a mu a protons actual weight is a fraction of a gram thus it is easier if we simplify this value to one atomic mass unit although a neutron is slightly heavier than a proton we will also simplify this value to 1 amu taking the weighted average of the two chlorine isotopes means we have to account for the fractional abundance of both of these isotopes thus the chlorine-35 isotope is the major isotope and its mass needs to be accounted for approximately 75% of the time while the mass of the minor isotope 3/7 needs to be accounted for approximately 25% of the time for simplicity we have rounded the fractional abundances and masses for both isotopes within our calculations as we expected the atomic mass 35.5 amu lies closer to the mass number of the more abundant chlorine-35 isotope in the previous carbon example we examine two isotopes of carbon the carbon 12 isotope is the major isotope and its mass needs to be accounted for ninety eight point eight nine percent of the time while the mass of the minor isotope carbon-14 needs to be accounted for one point one one percent of the time as we expected the atomic mass for carbon twelve point O one amu lies much closer to the mass number of the more abundant isotope thus the atomic mass of an element depends on both the mass and the relative abundance of each of the elements isotopes the third subatomic particle the electron is a negatively charged particle that resides outside of the nucleus within orbitals in the next chapter we'll examine orbitals in much more detail but for now we will simply focus on how to ascertain the number of electrons that an atom possesses and how it affects the charge of the atom the actual charge that the positively charged proton and negatively charged electron possesses is very small thus for simplicity we will assign a positive 1 and a negative 1 charge to these subatomic particles if there are the same number of electrons as protons all charges will cancel and the atom will have no charge however if a different number of electrons than protons exists within an atom then the atom will have a charge called anion and this charge is written in the upper right-hand corner if an atom has more electrons than protons this ion is called an anion which has a negative charge and if an atom has less electrons than protons this ion is called a cation which has a positive charge for example if carbon gained an extra electron there would be one more electron than protons thus it would have seven electrons and a negative one charge in the next couple of examples it may help to think of an anion as an atom that has gained electrons and a cation as an atom that has lost electrons from the information given we do not need to consult a periodic table to deduce the number of protons for the fluorine 19 anion however if the atomic number of nine was not given we could have simply found fluorine on the periodic table and deduced its atomic number thus there are nine protons the number of neutrons is calculated from subtracting the number of protons from the mass number which gives 10 neutrons the negative one charge indicates there is one extra electron when compared to the number of protons thus there are 10 electrons here the atomic number of 12 is given for the magnesium 24 cation thus there are 12 protons again the number of neutrons is calculated from subtracting the number of protons from the mass number which affords 12 neutrons and finally the positive 2 charge indicates we have lost 2 electrons when compared to the number of positive charges thus there are 10 electrons this is always a good idea to check your work for example if you deduced there was 12 protons and 10 electrons you can simply add them together 12 positives with 10 negatives adds 2 plus 2 which matches the charge of this cation it is important to be able to quickly deduce the quantity of each of these subatomic particles so that you can gain a better understanding of the atom you are examining in fact different atoms have distinct chemical properties and reactivities due to the different numbers of protons neutrons and electrons now that we have developed skills to deduce numbers of protons neutrons and electrons for any isotope or ion let us start to get a feel for the relative sizes of these particles within an atom we have already learned that the proton is positively charged and the neutron has no charge that they both reside within the nucleus are about the same size and they are both approximately 2,000 times bigger than a negatively charged electron which resides in an orbital the term nucleus loosely translates to little nut in Latin [Music] so how small is the nucleus compared with the size of the orbital where the electron resides imagine you are standing in the middle of one half of a soccer field and you were holding a grain of rice in your hand which represents the size of a proton in this analogy now imagine the size of an electron which is one mm the size of that grain of rice this very small particle our electron moves rapidly and randomly inside this giant sphere with a fixed amount of energy this giant sphere is called an orbital which is the whole half of the field above and below you this is what an atom of hydrogen is like as you can see an atom is a whole lot of empty space even more in mind-boggling is the fact that an atom is so small that a human hair is approximately 1 million carbon atoms in width [Music] in the early 1900's many brilliant minds were changing the landscape of science in particular quantum theory was emerging and changing the way we viewed the atom one of the great results of quantum mechanics was the orbital which is where the electrons reside an orbital should never be confused with an orbit an orbit is a mathematically defined pathway for example how the Earth orbits the Sun using classical Newtonian physics we can predict where the earth will be on the orbit at some time T and where it was at some time T in the past you may have seen a similar simplified model of the atom where the electron is orbiting the nucleus on a mathematically defined pathway which couldn't be further from the truth an orbital is a much more complicated concept than an orbit in fact we know nothing about how the electron moves around the nucleus thus quantum mechanics demonstrated that electrons did not move around in neat orbits but existed in regions called orbitals with a fixed amount of energy in simplest terms an orbital is a three-dimensional region or shape and you can expect to find an electron inside the shape 90% of the time and may help to think of this shape as a boundary surface the electron is more likely to be inside this boundary shape rather than outside the boundary let's apply this concept of boundary shape to the electron of the hydrogen atom which has one proton in the nucleus and one electron in a surrounding orbital if you imagine the electron is moving in a random manner with fixed energy around the nucleus and then imagine that we take a picture of this electron every second for a day a week or month you see that all these pictures laid on top of one another begin to form an electron cloud around the nucleus remember all these hypothetical pictures or data points represent where the electron has been over time if we now attempt to create a three-dimensional surface to encompass 90% of all these data points we obtain a sphere which is often called the boundary surface the creation of this boundary surface for the hydrogen atom which is called an S orbital requires some pretty complex calculus thus if an electron is in an orbital the electron has a fixed amount of energy and the orbital is a three-dimensional region around the nucleus that indicates the probable location of that electron 90% of the time there are many different orbitals for the electrons to reside the success of solutions or orbitals from quantum mechanics increase in relative energy when we add the shapes to the energy turns we get the following electron configuration diagram which shows all the orbitals available for electrons to reside the orbitals fall into one of four broad categories s P D and F orbitals interestingly there is one solution each time an S orbital is obtained three solutions of the same energy each time a P solution is obtained five solutions are the same energy each time a D solution is obtained and seven solutions of the same energy each time an F solution is obtained in the next chapter we will revisit this diagram in detail to aid in writing electron configurations for now let's just focus on what this diagram represents the orbitals and each of these lines abstractly represents an orbital for example the first line on the electron configuration diagram is the 1s orbital and it is a sphere this is where the first two electrons of an atom can be found 90% of the time in addition all of the s orbitals are shaped like fears the three 2p orbitals are shaped like dumbbells oriented along the three axis the 2px 2py and 2pz for convenience your instructor will often shrink them down to a third of their size so that they are easier to draw if we continue to go up and relative energy the shapes of the orbitals become increasingly more complicated as demonstrated by the 3d orbital shapes and it is unlikely that your instructor will hold you accountable before these shapes although this diagram may look complicated remember that each line abstractly represents an orbital and that all these orbitals overlap on the same atom here you can see that a 1s orbital is the first orbital that the electrons will reside in then the 2's orbital is on top of that then the three 2p orbitals on top of them and so on and so on until the necessary amount of orbitals are present to house all of the electrons that an atom may possess if orbitals are where electrons can be found 90% of the time in the next chapter we will examine how many electrons are in each orbital and the order in which they are filled by an atom [Music] the arrangement of electrons in an atom is known as the atoms electron configuration think of this as finding a home for each electron electrons want to be in the lowest energy arrangement called the ground state electron configuration and to accomplish this we need to follow three basic rules the off-ball principle tells us the order the orbitals are filled alfe ball is a german word meaning to build up just like building a house we need to start at the bottom floor when that is completely finished we begin on the next floor thus electrons are added to the lowest energy orbital first and then we work our way up in relative energy this means that on the electron configuration diagram electrons are placed into the 1s orbital first then the 2s followed by the 2p 3s 3p and so on and so on until the necessary amount of orbitals are filled to house all the electrons that an atom may possess the next rule is called the Pauli exclusion principle which simply translates to only 2 electrons per orbital with opposite spin within the electron configuration diagram we will represent electrons as 1/2 arrows the first arrow is up and the second arrow is down remember that each line on this diagram abstractly represents an orbital and that each arrow represents an electron in that orbital below the diagram is the electron configuration notation which utilizes exponents to indicate the number of electrons within each orbital the third and last rule is called hoons rule which states orbitals of equal energy are occupied by one electron before any orbital is occupied by a second electron now let's review these three basic rules the first electron goes into lowest energy orbital 1s orbital which is the Aufbau rule the second electron goes into that same orbital with opposite spin the Pauli exclusion principle states we can only have two electrons per orbital thus the third electron goes into the next highest energy orbital the two the fourth electron also goes into the 2's orbital but with opposite spin followed by the fifth electron filling one of the 2p orbitals hoon's rule states that the six electron will go into a different 2p orbital because we should fill the orbitals one at a time across an energy level before pairing electrons subsequent electrons are added following these three basic rules until the required amount of electrons are added to work this example problem we first need to consult the periodic table to ascertain how many electrons are in a neutral atom of carbon in the first chapter we learned how to quickly deduce the number of electrons and we will need this skill now the atomic number of carbon is 6 thus a neutral atom of carbon has 6 electrons therefore this problem simply translates to finding a home for 6 electrons following our three simple rules we place all six electrons into our diagram as shown start at the bottom working our way up two electrons per orbital with opposite spin and fill the orbitals one at a time across an energy level before pairing electrons in this example we have one more electron than the atomic number of fluorine thus examining the periodic table we see that fluorines atomic number is nine which means there are nine protons and ten electrons if we have a negative one charge thus the problem is really asking us to find a home for 10 electrons again following our three simple rules we place all 10 electrons into our diagram as shown in this example the calcium atom has lost two electrons when compared to the number of protons thus examining the periodic table we see the calcium città McNutt wente which means there are 20 protons and 18 electrons if we have a positive 2 charge thus the problem is really asking us to find a home for 18 electrons again following our three simple rules we place all 18 electrons into our diagram as shown [Music] first we need to consult the periodic table to ascertain how many electrons are in a neutral atom of gallium which will be the same as the atomic number for gallium gallium atomic number is 31 which means there are 31 electrons if gallium has no charge thus the problem is really asking us to find a home for 31 electrons again following our three simple rules we place all 31 electrons into our diagram as shown [Music] you are probably thinking that it is going to be very challenging to memorize and reproduce the electron configuration diagram template shown however if you have access to a periodic table you can easily reproduce it for example if you simply read the periodic table from left to right the correct order of orbital filling is obtained 1s 2s 2p 3s 3p 4s then you go down a level for the 3d back up to the 4p 5s down a level for the 4d and so on in addition the periodic table tells us how many electrons go into each sublevel for example the s block is 2 elements across the Stu electrons can go into all the s sub levels the P block is 6 elements across the 6 electrons can go in all the P sub levels the D block is 10 elements across thus 10 electrons can go in all the D sub levels and finally the F block is 14 elements across which means 14 electrons can go in all the F sub levels you may notice that when we compare the order of filling we obtained from the periodic table to the electron configuration diagram template they are the same clearly having access to a periodic table helps us reproduce the electron configuration diagram template thus you should practice drawing this diagram on your own with the aid of a periodic table until you have mastered this skill as you can tell the keys to writing electron configurations are to quickly ascertain the number of electrons for an atom or ion from the periodic table and to be able to quickly reproduce the template for the electron configuration diagram remember you can use the periodic table to help you reproduce it then simply follow the three basic rules for electron configurations and you should have no problems determining electron configurations [Music] in the last chapter it may have seemed difficult representing electron configurations and drawing the full electron configuration diagrams for atoms that possessed many electrons for example the 31 electrons that are found in a neutral atom of gallium fortunately there is a much easier way abbreviated electron configurations allows to combine the inert noble core electrons with the remaining outermost electrons therefore to be able to write the abbreviated electron configuration we need to first become familiar with noble core electrons the noble core electrons have the same electron configuration often termed isoelectronic as a noble element to better understand noble core electrons let's return to the previous gallium example recall the galleons atomic number was 31 which meant we found a home for the 31 electrons of a neutral atom of gallium the noble elements are the last family on the periodic table to abbreviate the noble core electrons for gallium we simply slide back until we reach the first noble element which is argon argon has 18 electrons thus we can abbreviate the first 18 electrons of gallium as the element argon these 18 electrons begin at the 1s and end at the 3p orbital and are represented by the noble element argon in brackets clearly the abbreviated diagram is much easier to draw than the full electron configuration diagram [Music] in this example we will first draw the full electron configuration diagram for a neutral atom of potassium then we will focus on the abbreviated versions potassium città Makhno 19 which means there are 19 electrons for a neutral atom of potassium following the Alpha rule Pauli exclusion principle hoons rule the following diagram and electron configuration is quickly obtained for the 19 electrons of potassium to abbreviate the noble core electrons for potassium we simply slide back until we reach the first noble element which is argon with 18 electrons thus we can abbreviate the first 18 electrons of potassium as the element argon the first 18 electrons of potassium which begin at the 1s and ended the 3p orbital are represented by the noble element argon in brackets the remaining electron in the 4s orbital is the outermost electron commonly called the valence electron it is often very important to quickly ascertain the number of valence electrons than an atom possesses after all these are the electrons that will be involved in bond making and bond breaking the noble core electrons will not be involved in bond making and are often called the inert noble core electrons thus let's focus our efforts on the reactive valence electrons to answer how many valence electrons carbon has we will first write the abbreviated electron configuration we see that a neutral atom of carbon has six electrons thus the electron configuration for the six electrons of carbon is 1s2 2s2 2p2 however we need to write the abbreviated electron configuration to answer this question thus we slide back to the nearest noble which is helium helium will represent the two noble core electrons which leaves four valence electrons it should be noted that we did not have to draw the full or the abbreviated electron configuration diagram to answer this question we just needed access to a periodic table for example if we first slide back to the nearest noble which is helium then we can simply count forward to the element in question and that will equal how many valence electrons that atom possesses one two three four valence electrons which matches our result from drawing the electron configurations [Music] let's try to answer one more of these questions using only the periodic table for phosphorous for example if we first slide back to the nearest noble which is neon then we can simply count forward to the element in question and that will equal how many valence electrons that atom possesses which is five valence electrons thus from the periodic table we see that there are ten noble core electrons which we could represent by placing neon and brackets and the remaining five valence electrons are placed into the 3s and 3p orbitals which matches the diagrams shown having the ability to quickly ascertain the number of valence electrons and atom has is very important in bonding theory which is thoroughly examined in the next DVD of this series introduction to bonding [Music] the four quantum numbers are a direct result from various quantum mechanical equations these four quantum numbers completely describe where an electron can be located in a more simplified view one could say that the four quantum numbers give rise to the solutions or orbitals that the electrons occupy or that they give rise to the electron configuration diagram shown which was covered in Chapter two while thorough treatment of this topic is beyond the scope of this DVD your instructor may ask you to assign the four quantum numbers to an electron thus it is worth our efforts to learn about the four quantum numbers the four quantum numbers are the principal quantum number which will tell us the energy level the electron is located the angular momentum number which will indicate the shape of the orbital the magnetic quantum number which indicates on which axis the orbital is on and the spin quantum number which has only two possible values plus 1/2 which is up or minus 1/2 which is damn while this may seem confusing it is actually very easy to assign the four quantum numbers to an electron as the following examples we'll demonstrate [Music] after we draw the electron configuration diagram for nitrogen we see that the last electron occupies a 2p atomic orbital thus the principal quantum number which represents the energy level is 2 the second quantum number the angular momentum number represents the shape of the orbital and from the chart if the electron is in a p orbital l is equal to 1 the third quantum number the magnetic quantum number M have the designations shown from minus L to plus L thus this electron in the last 2p orbital has the value of +1 and the last quantum number which indicates the spin of the electron is plus 1/2 because the electron is pointing up thus the four quantum numbers are 2 1 plus 1 and plus 1/2 [Music] in the next example we are asked to assign the four quantum numbers to the last electron of a chloride anion from the electron configuration diagram we see that we need to fully describe the last three P electron the electron is in the third energy level thus and is three it occupies a p orbital thus L is 1 M is +1 and the electron is pointing down therefore it is minus 1/2 thus the four quantum numbers are 3 1 plus 1 and minus 1/2 in the next example we are asked to assign the four quantum numbers to the last electron of an atom of titanium from the electron configuration diagram we see that we need to fully describe the second 3d electron the electron is in the third energy level thus and is 3 it occupies a D orbital thus L is 2 M is minus 1 and the electron is pointing up therefore it is plus 1/2 thus the four quantum numbers are 3 2 minus 1 and plus 1/2 if chemistry is considered to be the central science than having a basic understanding of the atom and the three fundamental sub atomic particles the proton the neutron and the electron is essential after all the student who has the ability to understand the atom can take the next crucial steps to comprehend many different aspects of chemistry [Music]

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Keywords: Quantum Theory, Orbits vs. Orbitals, Orbital Shapes, Electron Configuration Diagram, Writing Full Electron Configurations and Diagrams, Aufbau Rule, Hünd's Rule, Pauli Principle, and Connection between Periodic Table and Order of Filling for Electrons, education, chemistry, atom, orbital, electron, configuration, periodic, high, school, learn, review, DVD, science, proton, neutron, exam, test, summary, cloud, dot, diagram

Id: 4YUWHWBrvI4

Length: 35min 35sec (2135 seconds)

Published: Tue Mar 12 2019