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Atomic Structure


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Atomic Structure

  1. 1. By iTutor.comT- 1-855-694-8886Email-
  2. 2. What is Atom? The smallest unit of matter that retains the identity of thesubstance. Atoms are the basic building blocks of matter that make upeveryday objects. A desk, the air, even you are made up ofatoms. There are 90 naturally occurring kinds of atoms. Scientists inlabs have been able to make about 25 more. Atoms are made out of three basic particles:Protons, Neutrons and Electrons.© iTutor. 2000-2013. All Rights Reserved Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of theatom. Electron Shell: region that surrounds the nucleus that containsmost of the space in the atom.Atomic Structure
  3. 3. What is Nucleus ? The nucleus of an atom contains protons and neutrons. Thenucleus carries a positive electrical charge. Electrons movearound outside the nucleus. Almost all of the mass of an atom is in its nucleus; almost allof the volume of an atom is occupied by electrons.ElectronProtonNeutronCarbon nucleus© iTutor. 2000-2013. All Rights Reserved Electrons are basically theconnectors in the process ofbonding. The bond is determinedby the amount of valenceelectrons the element has. Protons are positively charged, while Neutrons are neutral(hence the name), and attract the negatively charged electronsto the nucleus, where they both reside. Neutrons are also those who prevents the protons to get out ofthe nucleus.
  4. 4. © iTutor. 2000-2013. All Rights ReservedQuantum Theory The quantum mechanical model is based on quantum theory,which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know theexact position and momentum of an electron at the same time. The quantum mechanical model of the atom uses complexshapes of orbitals (sometimes called electron clouds orelectron shell), volumes of space in which there is likely to bean electron.
  5. 5.  The Bohr Model has an atom consisting of a small, positively-charged nucleus orbited by negatively-charged electrons. Electrons orbit the nucleus in orbits that have a set size andenergy. The energy of the orbit is related to its size. The lowest energyis found in the smallest orbit. Radiation is absorbed or emitted when an electron movesfrom one orbit to another.Bohr’s Model© iTutor. 2000-2013. All Rights ReservedThe Rutherford–Bohr model ofthe hydrogen atom (Z = 1) or a hydrogen-like ion (Z > 1), where the negativelycharged electron confined to an atomicshell encircles a small, positivelycharged atomic nucleus and where anelectron jump between orbits isaccompanied by an emitted or absorbedamount of electromagnetic energy (hν).
  6. 6. © iTutor. 2000-2013. All Rights ReservedThe orbits in which the electron may travel are shown as grey circles;their radius increases as n2, where n is the principal quantum number.The3 → 2 transition depicted here produces the first line of the Balmerseries, and for hydrogen (Z = 1) it results in a photonof wavelength656 nm (red light).Limitation of Bohr’s Model It is in violation of the Heisenberg Uncertainty Principle. TheBohr Model considers electrons to have both a known radiusand orbit, which is impossible according to Heisenberg. The Bohr Model is very limited in terms of size. Poor spectralpredictions are obtained when larger atoms are in question. It cannot predict the relative intensities of spectral lines. It does not explain the Zeeman Effect, when the spectral lineis split into several components in the presence of a magneticfield. The Bohr Model does not account for the fact that acceleratingelectrons do not emit electromagnetic radiation.
  7. 7. Calculate the number of Protons, Neutrons and Electron The atomic number is the number ofprotons in an atom of an element. Inour example, kryptons atomicnumber is 36. This tells us that anatom of krypton has 36 protons inits nucleus.AtomicNumberAtomicweight© iTutor. 2000-2013. All Rights Reserved The atomic weight is basically a measurement of the totalnumber of particles in an atoms nucleus.To find the mass number, all you need to do is round theatomic weight to the nearest whole number. In ourexample, kryptons mass number is 84 since its atomicweight, 83.80, rounds up to 84.Mass Number = (Number of Protons) + (Number of Neutrons)84 = 36 + (Number of Neutrons)Number of Neutrons = 84-36Number of Neutrons = 48
  8. 8.  Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36electrons since it contains 36 protons.In SummaryNumber of Protons = Atomic NumberNumber of Electrons = Number of Protons = Atomic NumberNumber of Neutrons = Mass Number - Atomic NumberCall us for moreInformationwww.iTutor.comVisit1-855-694-8886