Flashcards
1. Atomic structure
Flashcards do conjunto (89)
- 1Elementa substance whose atoms all have the same number of protons made of only one kind of atom and cannot be broken down into simpler substances
- 2Theorysubstituted for those parts of reality that are not yet discovered or understood and proposes an explanation for the phenomenon
- 3acceptable theories should belogical and show congruence between the present body of knowledge and theoretical constructs
- 4data collected must beaccurate, reliable and replicable
- 5as the body of knowledge increasestheoretical adjustments must be made to overcome contradictions within the scientific society
- 61808 John Daltondeveloped the first useful atomic theory of matter. Some of Dalton's theories are now known to be incorrect but the basic concepts are the foundations of modern science
- 7Assumptions of Dalton's Atomic Theory1. Matter consists of small particles called atoms
2. Atoms are indestructible or indivisible
3. Atoms of same element are identical in mass and properties
4. Atoms combine chemically in simple whole number ratios to form compounds
5. Atoms can combine in more than one simple whole number ratio - 8With the discovery of subatomic particles it was possible to show thatthe atom could be divided into smaller parts
- 9Errors in Dalton's Atomic Theory1. Atoms are not indivisible, it can be divided into smaller parts (subatomic particles)
2. Atoms are not indestructible- it can be destroyed by nuclear reactions
3. All atoms of the same element are not identical- atoms of the same element with different masses exist (isotopes) - 10indivisibleunable to be divided or separated
- 11atomSmallest particle of an element
- 12moleculea particle that contains 2 or more atoms chemically joined together
- 13Cathode rays consist ofelectrons
- 14Electronsnegatively charged particles about 1840 times lighter than hydrogen atoms
- 151897 JJ Thomsondiscovered electrons
- 16How Thomson discovered the electronhe deflected cathode rays with both electric and magnetic fields. He reasoned that if a particle had momentum, it must have a mass, thus cathode rays must be a stream of particles. He used the results to measure the charge to mass ratio and found these particles to be negatively charged and had a mass nearly 2000 times lighter than the mass of a hydrogen atom.
- 17Thomson work made it apparent thatatoms were not indivisible and gave evidence for the existence of subatomic particles
- 18the model that JJ Thomson proposePlum pudding model which described atoms as negative charged electrons embedded in a sphere of positive charge
- 191900 E. Goldsteindiscovered protons after observing the rays in a cathode ray tube that were travelling in the direction opposite to that of cathode rays. According to Goldstein since atoms are electrically neutral they must contain equal number of positively charged particles to negatively charged particles
- 201909 Earnest Rutherford and colleagues Geiger and Marsdenbombarded thin metal foils with alpha particles to test Thomson's model of the atom. Rutherford and his colleagues found that most of the alpha particles passed straight through the foil, showing that they must have passed through essentially empty space. However, a small portion of the alpha particles were deflected at very large angles, and a few even bounced back towards the source. This indicated that strong forces were present to cause deflection of the alpha particles
- 21Rutherford proposedthat most of the atom must be mainly empty space with the mass and positive charge being concentrated in a tiny nucleus while the electrons orbit the nucleus like planets orbit the sun.
- 22Rutherford planetary model of the atom did not explainwhy the negative electron revolving a positive nucleus did not lose energy and spiral into the nucleus or what prevented the electrons from being pulled into the nucleus by electrostatic attraction
- 231913 Niels Bohrproposed an atomic model based on the quantum theory in which electrons move around the nucleus in definite orbits. Niels Bohr worked out that the electrostatic force between the nucleus and an orbiting electron was cancelled out by the outward force due to orbital motion. Bohr suggested that an electron in a given orbit can have only a certain amount of energy and the orbit can have only a certain radius.
If the electron absorbs a quantum of energy, it moves to an orbit with a higher energy level which is further away from the nucleus. The electron becomes excited and emits energy to returns to its stable orbit. - 24late 1913 Henry Moseleysuggested that if atoms are neutral, then the number of electrons must be the same as the number of protons. Since electrons have negligible mass, and the atomic masses are greater than the mass of protons in the atom the extra mass must be the existence of a particle with mass but no charge. Rutherford also put forward this idea and called the particle a neutron. Thus began the search for the neutron
- 251932 James Chadwickbombarded the element Be with alpha particles. This produced a highly penetrating stream of particles which could pass through many centimeters of solid lead and which was not deflected by electric or magnetic fields. he had detected the neutron. James Chadwick discovered the neutron
- 26the word atom comes fromthe greek "atomos" which means something that cannot be split into smaller pieces
- 27atoms are considered ____ and consist of_______the building blocks of chemistry______ protons, neutrons and electrons
- 28where protons, electrons and neutrons are foundheld in a tiny nucleus by powerful nuclear forces while the electrons are found orbiting the nucleus
- 29The mass of the subatomic particles is measuredrelative to one twelfth the mass of a carbon-12 isotope
- 30the charge of the particles iscompared to the charge of a proton and an electron
- 31mass of proton1 amu
- 32mass of neutron1 amu
- 33Mass of an electron1/1837
- 34Charge of a proton+1
- 35charge of a neutron0
- 36charge of a electron-1
- 37the structure of the atom is held together bythe electrostatic force of attraction between the + charged nucleus and the - charged electrons surrounding it
- 38Experiments in which subatomic particles are deflected in electric and magnetic fields showelectrons are deflected at large angles towards the positive pole (which suggests that electrons are negatively charged particles and lighter than protons) while protons are deflected at smaller angles towards the negative pole (and protons are positively charged particles) and neutrons showed no deflection (which suggests that these particles do not carry an electric charge and are therefore neutral
- 39diagram behavior of particles in an electric fielddiagram
- 40Atoms are electrically neutral species sothe number of protons must be equal to the number of electrons
- 41Atomic (proton) numberthe number of protons in the nucleus of an atom
- 42the atomic number is used to define the atom becauseAtoms of the same element have the same number of protons
- 43atomic mass/mass numberthe sum of protons and neutrons in the nucleus of the atom
- 44the atomic mass is also referred to as the nucleon number sincethe protons and neutrons are found in the nucleus of the atom
- 45who discovered isotopesThomson found isotopes in 1913 when he saw that some atoms of the same elements had different masses
- 46Isotopesatoms with the same atomic number but different mass numbers
- 47Isotopes of an element have the same atomic number becausethey have the same number of protons but the difference in mass numbers is due to the different numbers of neutrons present
- 48Why isotopes have the same chemical properties but different physical propertiesSince the number of protons is equal to the number of electrons, isotopes have identical chemical properties, however, their physical properties are different because they have different masses
- 49how many isotopes do elements consist ofmore than one isotope
- 50chlorine exist with mass number35 and 37.
Chlorine 35 contains 17p, 18n while
Chlorine 37 contains 17p, 20n - 51The proportion of each isotope in a given element is calledthe relative abundance
- 52The relative abundancethe ratio or percentages in which they exist in the world.
- 53If the relative abundance is minute and is insignificant then itis not considered in calculating the relative atomic mass for placement in the periodic table
- 54although isotopes of elements exist, the relative atomic masses arewhole numbers whereas there are some whose masses are not whole numbers.
- 55The mass of an element depends onthe relative abundance of the isotopes present in the element.
- 56The actual mass of an atom is sosmall that it is not practical to work with therefore a reference is used and compared to the actual atomic mass
- 571961- it was agreedinternationally that the carbon 12 isotope should be used as the reference
- 58the mass of an atom relative to (compared to) the reference is calledthe relative atomic mass
- 59The relative atomic massthe average weight and relative abundances of the isotopes of elements in naturally occurring samples are measured
- 60the relative atomic mass is not usually a whole number becausethe mass of an atom compared to one twelfth the mass of a carbon 12 isotope.
- 61the relative isotopic massthe mass of a single isotope compared to one twelfth the mass of a carbon 12 isotope
- 621919 F. Astondeveloped the mass spectrometer
- 63the mass spectrometer is used tomeasure the mass an relative abundance of each isotope in a sample of naturally occurring element
- 64main steps involved in the operating principles of the mass spectrometer1. Ionization
2. Acceleration
3. Deflection
4. Detection - 65Ionizationthe sample of the element is vaporized and injected into the instrument.
The element passes into the ionization chamber where the atoms are bombarded by a beam of high energy electrons which knocks one ore more electrons out of the atoms converting them into positively charged ions - 66AccelerationThe positive ions move into the accelerating chamber where an electric field accelerates positive ions towards a magnetic field.
- 67deflectionThe fast moving ions are deflected according to their mass and charge as they pass through the magnetic field. Ions with lower mass to charge ratios are deflected more than ions with higher mass to charge ratios
- 68detectionThe ions are detected by an instrument which is attached to an amplifier and a recorder. When the accelerating electric field and the magnetic field are kept constant, only ions of a specific mass to charge ratio can be detected. Higher or lower mass to charge ratios are either deflected too little or too much to make contact with the detector. Therefore by varying the electric field and magnetic field strength, one isotope after another can be deflected to hit the detector. The mass and the relative abundance of each isotope can be measured and an accurate value for the relative atomic mass can be calculated. The relative heights of the peaks produced by the recorder give a measure of the relative abundance of the different isotopes present.
- 69diagram how the mass spectrometer worksaaa
- 70the mass spectrum of chlorine atoms shows the relative abundance of chlorine-35 is 75.8% and chlorine-37 is 24.2%. calculate the relative atomic mass (Ar) of chlorine35.5
- 711903 Henri Bacquerel was awardedthe Nobel prize for physics for his discovery of radioactivity
- 72how Henri Bacquerel discovered radioactivityBacquerel wrapped uranium covered photographic plates in black paper and placed them in a drawer for a few days. he found that clear images were developed on the plates which suggested that uranium emitted radiation. he later showed that the radiation emitted were not only similar to X-rays and could also be deflected by a magnetic field which suggests that they consist of charged particles
- 73how the Curie's discovered radioactive elements radium and poloniumPierre and Marie Curie were interested in the recent discovery of radiation and conducted research on radioactive substances. they found that uranium ore contained much more radioactivity than could be explained by the uranium content alone. the curie's research led them to the discovery of the radioactive elements radium and polonium. they shared the nobel prize for physics with Bacquerel in 1903
- 74marie received a second nobel prize in 1911 forchemistry for her isolation of radium. her research in radioactivity was immediately applied to the treatment of cancer and other diseases
- 75what the Curie's discoveredthe radioactive elements radium and polonium
- 76the force of attraction in the nucleusis a strong nuclear force of attraction that exists between nucleons. the nucleons are intimately involved in this attractive force
- 77as the number of protons increases in the atom the positive charges in the nucleusrepel each other so that the number of neutrons needed to create a stable nucleus increases more rapidly than the number of protons
- 78even with an increasing number of neutrons to protons in the nucleusnuclei with 84 or more protons are unstable
- 79unstable nuclei are calledradioisotopes (radioactive isotopes)
- 80unstable nuclei become stable byspontaneously ejecting alpha particles, beta particles and gamma radiation.
- 81the emission of alpha and beta particles changesthe number of protons in the nucleus so that a different atom is produced
- 82Alpha particles arehelium nuclei
- 83in nuclear reactions it is understood thatalpha particles are formed without its electrons therefore the symbol "He" is used in nuclear equations
- 84Emission of alpha particles leads to adecrease in atomic number by 2 and mass number by 4
- 85eg of emission of alpha particlesaa
- 86beta particles are formed whena neuron disintegrates giving a proton and an electron. the proton remains in the nucleus of the atom, so its atomic number increases by 1. the mass number is unchanged
- 87eg of beta particles forminga
- 88Gamma rays areelectromagnetic waves of short wavelength
- 89emissions of alpha or beta particles are often accompanied bythe emission of gamma rays
Informações
- Descrição
- Atomic theory atomic structure
- Criado por
- victoria acevero
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