The Evolution of Atomic Structure _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ In this book series I am going to explain everything thing about atom its part 1- evolution of atomic structure Part 2 - behind the atom Part 3 - i am hear the atom In second part Bond and bonding in the final part particles physics with all knowledge of atom CONTENTS _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Part 1 classic mechanics Part 2 quantum foundation Part 3 particles physics Part-1 All this started around 400BCE or 2,395 years ago. The philosopher Democritus thought that an apple if divided into half and half and half but a moment came when it could not divide more it is called ‘ATOMOS’ no experiment just philosophy. He also said that the atomos they show show different - different properties. In the same period the Indian philosopher Maharishi Kanad . He says that the smallest particles are called 'ANU’. John Dalton he proposed the first model of atom with 6 postulates 1. Each and every object in this universe is made up of tiny particles called atom 2.Atoms of the same element are identical in mass and properties 3.Atoms of different elements are different in mass and properties. 4.atom can not create or destroy in chemical reaction only they can rearrange 5.Atoms combine in simple whole number ratios to form compounds. [after some pages we will seen it in very brief] 6.In a given compound, the kind and number of atoms remain fixed . In water [hydrogen and oxygen] it's 1:8 if it doesn't then it's not water . This ratio is by Mass. J. Dalton describes is a British teacher the theory by two laws. law Conservation of Mass & law of definition proportion. Dalton also gives symbols of elements . The atom is a solid sphere. Mass is neither created nor destroyed in a chemical reaction. By Antoine Lavoisier A compound always contains the same elements in the same fixed ratio by mass. By Joseph Proust Drawbacks of Dalton atomic theory 1. Atoms are not indivisible; they can be divided into electrons, protons, neutrons. Even e-,p + ,n 0 are made up of quarks 2. John says that all atoms of the same element are identical.and he is here Because isotopes eg- Cl-35,Cl-37. 3. Atoms can be destroyed in nuclear reactions. But we can separate them from nuclear fusion or fission. 4. Does not explain the structure of atoms. He says the atom is a solid sphere. 5. Doesn't explain how the atoms make bonds but nowadays modern physics tells how the atoms make bonds. Atomic Model of J. J. Thomson (1904) 1. Atoms are positively charged sphere 2. Electrons are embedded between the positive charge.He found the electrons 3. The positive & negative charges are equal 4. Atoms are electrically neutral. Drawbacks of J.J Thomson 1. Thomson model says that the positive change is evenly distributed but in in the centre 2. Electrons are embedded between the positive charge. But the electrons rotate around the nucleus and the nucleus is made up of protons and neutrons. 3. Did not explain how they move 4. Did not explain the stability of atom 5.failed to explain emission or absorption spectra of elements. Cathode Ray Tube (CRT) Experiment — 1897 1.requirements Glass tubes with most of the air removed add very low pressure gas. Two metal electrodes. Super High voltage power supply Fluorescent screen to detect the beam Electric and magnetic plates to test the charge of the particles 2. Prossger A very high voltage ray was produced from cathode towards anode. When the beam struck the fluorescent screen, it produced a glowing spot.we put a magnetic were to observe how the beam behave.so what happens when we put the magnetic so see in paragraph. 3. Observations So the ray travels towards the anode. A ray moves in a straight line. When we apply a magnetic field we see rays deflected. an electric field is applied, the rays bend toward the positive plate. 4. Conclusions But why was the ray bent? Because in ray some is negatively charged. So something in the atom that is negatively charged. And the negative charge is called electrons. Atomic Model of Ernest Rutherford (1911) 1. Atoms have a very small,dense positive charged nucleus in the centre 2. Most of the mass of atoms is concentrated in the nucleus. 3. Electrons revolve around the nucleus in a circular way. ( Now day it's a common thing but in that era it's a very big thing ) 4. Most of the space of the atom is empty Drawbacks of atomic theory of Rutherford 1.In the time period a great physicist james maxwell he say that any electricity charged thing move it radiate energy so the electron also 2.Failed to explain the hydrogen emissions spectrum 3.Dose not tell how the electron arranged in an atom 4. Does not tell how the atom do bonding We know all this theory because the sir Rutherford do a famous experiment that is called Alpha particles gold foil Scattering experiment. So the set up of the experiment. A source of alpha particles ( so what are the alpha particles? Alpha particles are nothing but it's He2+ , it's not a toy, it's radioactive , it can kill you easily ) ,think Gold foil, they get gold foil because it's the most malleable element in our universe until we find it. That's why they get gold to foil not because he have so much money & and a zinc sulphate screen to detect scattered particles and it is not visible for human eyes we want a microscope to see it because the He2+ is very small Observations In the Alpha particles gold foil Scattering experiment most of the alpha particles go straight from the gold foil, very few reflected on small angles And very few come back at ~180° . It proves that in the centre something in its central part is named as protons p + Now we are going to the second greatest model of atoms, the Bohr model of atoms . Let's go back in time so we have to go back in time to James Maxwell. He says that any electricity charged particle that moves it releases alternate electrical radiation . Radiation is nothing but electromagnetic waves . The electromagnetic radiation waves can be shorter or longer waves. Bohr’s model of atom 1.The first postulate comes with the stability of atom electrons in a fixed circular path or fixed energy state and the electrons can not lose in fixed orbit.and the fixed path or fixed energy level are called orbits and shells. He named and numbered the shells by n=1 for the closest one and went far and further from the nucleus by one orbit to the second orbits also named as K,L,M,N . See the diagram After that he tells how to fill electrons by the formula 2n 2 2.He found the radius of atom in of shell to calculate the radius of atom In simple terms we write as Z = atomic number n = shell number Å = unit of length 10 -10 = 0.1nm h = plank constant me = mass of electron 9.1093837 × 10-31 kg So what is the sell size of (K)n=1 is 0.53Å And for n=2 is 2.11Å So do thinking something is missing. Yes it is Speed of electron the expression we use to find it By use we can the speed of e - So the n=1 is 2.186×10 6 meter per second is actually fast . But what about the energy and that is the 3 rd postulate. 3. The formula Bohr derive to calculate the energy if The total energy of n=1 first shell is -13.6ev ev is for electrons volt is the SI unit of energy Let's get the electron of the first shell. It can hold energy -13.6 it cannot be -13.4 or -13.2 but it never can go inside the nucleus . 4. His 4 th postulate says that electrons can lose and gain energy .The speed of waves is 300000 m/s calculated in vacuum but stays the same at every place they don't need medium to travel . The waves length is divided in many ways like radio waves,micro wave , infrared rays , visible light , Ultraviolet rays , x-rays and gamma-rays are the most dangerous . Humans only can see visible light that is 380 nm - 740nm . As we can if we pass a sun light beam through a prism. You can see continuous light red to violet and this is called visible light continuous spectrum because every light has different wavelengths so they show different colours. So the ordinary white light contains this red to violet. But the mystery stay for a long time continue when a white light pass through gasses the output is not coming as continuous spectrum it comes as spectrum for example : When white light enters hydrogen gas, the outcome is only that kind of patterns of color such as red,green, blue, and violet. It means that something in the hydrogen atoms absorbs remaining wavelengths .But here is a question: where does the radiation go? No doubt it goes in the atom but in which part it's great things to think about. In early time period we light is consistent and continues waves but light show particles features also and its called waves particles duality So now move to bohr’s hydrogen model of atom When the electron gain energy when it's in stationery state and then it can energy is moved stationary orbit to higher energy orbitals but we study in third first postulate of bohr that electrons have fixed energy so how they go in higher orbit it gains energy but the electron return to its stationary state or orbit when its energy actually I'm talking about electron release energy in the form of wavelength different-different wavelength show different different colours and electron go from stationery state to highest State orbit what that kind of electron called it called excited state but I like to say excited electron even both are correct but I prefer to excited state it's common in books. When the electrons radiate or release energy in the form of wavelength between 380 to 700 that shows these colours nm stand for nanometer. So it's the Bohr atomic model of hydrogen. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Part - 2 Heisenberg uncertainty principle In 1924 french physicist de broglie every matter had due nature like electromagnetic radiation meaning waves and particles behaviour according to him even humans are also waves but shorter wavelength but that is not detectable . But the sub atomic particles can be detected experimentally they have lesser mass so that's why In 1927 Germany physicist Heisenberg proposed that uncertainty principle he states that it's impossible to calculate the position and velocity at the same time of an electron because we see an atom by the help of light and light is Photon . After this theory physicists say that there is no fixed orbit so the orbit is replaced by the probability of the presence of electrons. Quant: energy is not contentious, it transfers in small small packets. Quantum model We can measure the location of particle but when it's wave how we measure the position when it is a wave it doesn't on a particular as it's in entire the atom When we observe the electron as particles.because our observations disturb the position of electrons it's not like the gas clouds its electrons cloud. By the Heisenberg uncertainty principle it's impossible to calculate the velocity and position at the same time; it's a fundamental limit. So scientists make some mathematical formulas. By Shödinger equations we find the electron in this particular region 90% of time but it is nearly to the 0.53Å. . But what the 10% of time it can anywhere close of nucleus far form nucleus but it can not leave atom.my some friends say something the electron is not in atom but atom is not atom with electrons all of the time electron stay in the atom far on near the nucleus . To understand the wave nature of particles we need more advanced mathematics, so in 1926 Erwin Shödinger . He is a physicist not a character of Attack on Titan but that is not the topic . So the in the 1926 he make waves equations understand quantum system so our quantum system is atom It explains the quantum system Currently our quantum system is atom . An electron cloud is a visual representation of probability density. The are the Shödinger equations for Electron hydrogen density of atoms in first energy (n=1). Do you remember this image? quantum numbers To understand atoms more deeply we have to know about quantum numbers. What are quantum numbers? Quantum numbers are nothing but it's the numbers that tell about electron states like size, shape, energy, spin, orientation . Most people face difficulty understanding. So the first is principal quantum numbers (n) shell no 1 see , shell no =2=n=2. in image: These n values are always positive . If n number increases also increases the electron cloud. Do you remember the formula of finding how many electrons in each shell 2n 2 .n is that number you see currently. It looks very simple but it's not . Azimuth number (l) or orbital quantum numbers If principle quantum numbers are housed, the Azimuth number is floor . There are 4 main subshells,p,d,f . Orbital Subhell 1n s 2n s,p 3n s,p,d 4n s,p,d,f And the l = (n-1) So see the next table Azimuth number (l) Subshell l=0 s l=1 p l=2 d l=3 f When Azimuth number (l) is 0 zero so it s orbital and its shape is sphere So l=1; its p orbital and its shape like a bumble. People and Books say but i don't think bumble So it's the d orbital ; l=2 .d z2 it's especially. Some books and people say it's a double bumble.