[Music] hi there have you ever wondered why fireworks have a different array of colors would you believe that this is due to the arrangement of electrons within the atom are you excited to discover more about the atom let's find out more in this video firework effects are produced by the combustion of explosive materials present in fireworks these explosive materials are also called metal salts metal salts emit a characteristic color of light when heated [Music] each color of light has a specific wavelength among the visible light red light has the longest wavelength and has the lowest energy violet light has the shortest wavelength and has the highest energy when compounds of different elements are heated over a flame it comes to a point where the hot gaseous atom begins to emit light of a definite color analysis of light given off by the vapors of elements can be done more precisely with an instrument called a spectroscope with the use of the spectroscope one can detect a series of narrow lines or line spectrum on the light given off by an element the spectral lines suggest different energy levels in an atom niels bohr a danish physicist explained the spectral lines of an element shown in the spectroscope each line in the atomic spectra of elements suggests definite energy transformations within the atom bohr stated that electrons are moving around the nucleus in a circular path or orbit at certain distances from the nucleus this movement is similar to the planets revolving around the sun which is why this model is also referred to as the planetary model electrons in each orbit have a definite energy this energy increases as the distance of the orbit from the nucleus increases these orbits are also known as shells or energy levels and are each assigned a number n equals one n equals two n equals three n equals four and etc or letters k l m n and etc as long as the electron stays in its given orbit there is no absorption or emission of energy if the electron received extra energy it can jump into a higher energy level this is also called the excited state the electron in the excited state can return to its original lower energy level or ground state by releasing a discrete amount of energy in the form of light moore's atomic model can only describe the atomic spectrum of an atom having only one electron like that of hydrogen irvine schrodinger together with werner heisenberg and louis de bruy made a refinement of boris atomic model schrodinger used mathematical equations to describe the possibility of finding an electron in a certain location this model is known as the quantum mechanical model of the atom based on the quantum mechanical model it would be impossible to plot a definite path or orbit for the moving electrons at least we can only guess the most probable location of the electron in a given instant to be within a certain volume or region of space surrounding the nucleus each energy level contains a certain number of sub-levels every sub-level has a fixed number of atomic orbitals an atomic orbital is the region around the nucleus where the electron is most likely to be found the atomic orbital serves as the house of the electron and it can accommodate a maximum of two electrons tracking down the location of a given electron in an atom is similar to tracking where a person lives to find a particular person you need to know his complete home address which should include the city street name and house number these correspond to energy levels sublevels and atomic orbitals in an atom in order to track where all the electrons in an atom are chemists use notations called electron configuration this electron configuration is the most stable arrangement in which the electrons have the lowest energy an s orbital is spherical in shape as the wave function suggests there is a 90 probability of finding an electron within the sphere except at its center where the nucleus is found a p orbital is dumbbell shaped the three equivalent p orbitals are p sub x p sub y and p sub z there are five kinds of d orbitals d sub y z d sub x z d sub x y d sub x squared minus y squared and d sub z squared except for the d sub z squared these orbitals consist of four lobes in contrast to the two lobes of the p orbital there are seven f orbitals these orbitals have the most diffuse shape compared to the other orbitals in the electron configuration of 1s2 1 refers to the main energy level occupied by the electron s denotes the kind of orbital and the superscript 2 for the number of electrons in the orbital the main energy level also tells us the number of sub-levels and the name of the sub-level is also the same with the name of the orbital three rules are applied in deriving the electron configuration these are off-both principle pauli's exclusion principle and han's rule of multiplicity oathbos principle is also known as the building up principle it states that electrons must first occupy the orbitals with lower energies than those with higher energies it follows this pattern or sequence in filling up the orbital the first orbital that is assigned two electrons is the 1s followed by two electrons for 2s and another 2 for each 2p orbital with a total of 6 for p sub x p sub y and p sub z this sequence goes on until all the electrons in an atom have been assigned to orbitals note that the maximum number of electrons for the s orbital is 2 6 for the p orbital 10 for the d orbital and 14 for the f orbital let's try writing the electron configuration for certain elements lithium with three electrons will have the electron configuration of 1s2 2s1 sodium which has 11 electrons will have the electron configuration of 1s2 2s2 2p6 3s1 now we're done with the first rule let's move on to the next rule which is paulie's exclusion principle according to pauli's exclusion principle only a maximum of two electrons can occupy an orbital and they must have opposite spins to minimize repulsion between them to give you a better idea let's try this example consider again our example earlier of lithium which has the electron configuration of 1s2 2s1 its orbital diagram would look like this not like this this follows poly's exclusion principle that electrons must have opposite spins to minimize repulsion between them for sodium its orbital diagram would look like this now let's proceed to the last rule which is hunt's rule of multiplicity according to hunt's rule of multiplicity when electrons enter a sub-level with more than one orbital they will spread out to the available orbitals with the same spin before pairing to better understand this rule let's have an example consider the electron configuration an orbital diagram of nitrogen which has seven electrons as you can observe the electrons in the p orbital have spread out first to the available orbitals with the same spin before pairing oxygen which has eight electrons will have this orbital diagram fluorine with nine electrons will have this orbital diagram now let's wrap things up war's atomic model also known as the planetary model describes the atom like a solar system where the electron is like a planet and can be found only in specific circular paths or orbits around the nucleus electrons in each orbit have a fixed energy an electron can jump to a higher energy level by gaining energy and returns to a lower energy level by releasing energy in the form of light the quantum mechanical model of the atom describes the atom as having a nucleus at the center around which the electrons move this model describes a region in space where the electron is most likely to be found the distribution of electrons in the different atomic orbitals is called electron configuration lastly three rules are applied in deriving the electron configuration these are off-both principle paulie's exclusion principle and hunt's rule of multiplicity that's all for now we will be discussing about ionic and covalent bonds in our next lesson so 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