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Chemistry
Atomic Structure P1
| Question | Answer |
|---|---|
| Who hypothesized that matter was made up of smaller particles | Democritus |
| State Dalton's Atomic Theory | 1. Matter consists of tiny indivisible particles. 2. Atoms of an element cannot convert into atoms of another element. 3. Atoms of a given element are identical. 4. Atoms of different elements combine with each other. |
| What do we know now as it relates to Dalton's Atomic Theory | 1. Atoms are not indivisible (subatomic particles) 2. Atoms of an element can be converted into atoms of another during nuclear reactions not chemical reactions. 3. Atoms of a given element have slight differences in their mass and properties (ISO) |
| What do we know now as it relates to Dalton's Atomic Theory cont'd | 4. True that most compounds can combine with each other but a few have slight differences in their atomic ratios |
| Who discovered the electron | J.J. Thomson |
| Who discovered the proton | Rutherford along with his colleagues Geiger and Marsden |
| Who discovered the neutron | H.B. Moseley postulated that there has to be a neutral particle seeing that the mass of the nucleus was greater than the mass of protons. James Chadwick experimented by bombarding α parti. with element Be |
| Describe in detail the discovery of the electron | Thomson deflected cathode rays in electric field produced by pair of metal plates. The negatively charged plate repelled the cathode rays while positively charged metal plate attracted them. Therefore electrons are neg. charged |
| Describe in detail the discovery of the proton | Rutherford bombarded metal foils with α. Discovered that most of α passed straight through foil, showing they passed through empty space. However, small portion of α was deflected at large angles, some bounced back to source. Strong force = defl. |
| What is the plum pudding model of the atom | This model (by JJ Thompson) shows that the atom is a sphere of positive charge and negatively charged electrons embedded in it to balance the total positive charge. |
| Charge on proton | +1 |
| Charge on electron | -1 |
| Charge on neutron | 0 |
| Position of proton | nucleus |
| Position of neutron | nucleus |
| Position of electron | energy levels |
| Mass of proton | 1 |
| Mass of neutron | 1 |
| Mass of electron | 1/1840 |
| Behavior of proton in electric and magnetic field | deflected towards negative plate |
| Behavior of neutron in electric and magnetic field | continues in a straight line |
| Behavior of electron in electric and magnetic field | deflected towards positive plate |
| Define isotopes | Isotopes are atoms of the same element with the same number of protons but different number of neutrons hence they have different mass # |
| Formula to calculate atomic mass when given isotopic abundance | (mass # of isotope x abundance %) / 100 |
| List the steps involved in mass spectrometry | 1. Ionization 2. Acceleration 3. Deflection 4. Detection |
| Who created the planetary model | Rutherford |
| What did Niels Bohr do | He proposed an atomic model based on the quantum theory in which electrons move around the nucleus in definite orbits. |
| Define atomic number | Number of protons in the nucleus of an atom Also gives the number of electrons |
| Define mass number/atomic mass | Number of protons and neutrons in the nucleus of an atom |
| Another term for atomic mass | Nucleon # |
| What is the relative abundance of an isotope | The proportion of each isotope in a given element |
| Relative atomic mass meaning | The weight in grams of the number of atoms of the element contained in 12g of carbon-12 |
| Relative isotopic mass meaning | The mass of a single isotope compared to one twelfth the mass of a carbon-12 isotope. |
| What is a mass spectrometer used for | To measure the mass and relative abundance of each isotope in a sample of naturally occurring element |
| Describe ionization in mass spectrometry | Atoms of the gaseous element are bombarded by high energy electrons which knocks one or more electrons of the atom converting them to cations. |
| Describe acceleration in mass spectrometry | Electric field will accelerate the positive ions towards a magnetic field |
| Describe deflection in mass spectrometry | Fast moving ions are deflected based on their mass and charge as they pass through the magnetic field. Ions with lower mass to charge ratio will deflect more than ions with higher mass to charge ratio |
| Describe detection in mass spectrometry | Instrument is attached for detection to occur. Only specific ions will be detected as the electric and magnetic fields are kept constant By varying electric & magnetic field stren. one iso after the other can be detected |
| Define radioactivity | Radioactivity is the spontaneous disintegration of unstable atomic nuclei. The nucleus of the atom becomes more stable by emitting radiation in the form of alpha, beta or gamma rays. |
| Define radioisotope | an isotope with an unstable nucleus which undergoes radioactive decay by spontaneously giving off particles and radiation from its nucleus. |
| Give two uses of Cobalt 60 | 1. Food irradiation - sterilize food to increase shelf life 2. External irradiation - control cancerous growth |
| Use of carbon-14 | Allows for dating method which is used to determine the ge of an organism by using properties of radiocarbon |
| Use of iodine-131 | Used to treat thyroid cancer |
| Use of plutonium-238 | Generates significant heat; useful as a heat source for sensitive electrical components in satellites PT-239 used to make nuclear weapons |
| Use of uranium-235 | fuel for nuclear power plants |
| What is the Band of Stability | A plot of the number of neutrons vs the number of protons in stable nuclei which shows that stable nuclei are located within a shaded area. |
| How is repulsion between the positive charges of the protons minimized | Presence of neutrons in the nucleus |
| What happens as the atomic number of an element incerease | The neutron to proton ratio must also increase in order to keep the nucleus together. |
| Nuclei above the band of stability will have a _____ n/p ratio and can move toward the band of stability by emitting ______ | higher ; beta particle which will increase number of protons |
| Nuclei with atomic number greater than ___ tend to undergo ______ | 84; alpha emission which decreases both # of neutrons and protons |
| What is the evidence for atomic structure and arrangement of electrons? | Electromagnetic Radiation - a stream of particles with no mass travelling in a wave like pattern and moving at the speed of light (photons) |
| What is the absorption spectrum? | When white light passes through substances, the atoms absorb light of certain wavelengths. This causes a discontinuous spectrum with black lines in the spectrum indicating the wavelengths that were absorbed |
| What is the emission spectrum? | If the atoms are heated sufficiently, they will emit a light of certain wavelength. The observed spectrum will have colored lines displayed on a black background. |
| State Planck's Quantum Theory | Energy can be absorbed or emitted in certain amounts, packets of energy called quanta |
| Do electrons have energy? | Yes, electrons in orbit have a certain amount of energy - it is quantized |
| How do electrons move from one orbit to the next? | Electrons in orbit do not emit energy. For an electron to move from one orbit to the next, it has to absorb energy to be able to move away from the nucleus. |
| The _____ the difference in energy levels the higher the ________ of emitted light | greater; frequency |
| Alpha emission removes..... while beta emission removes...... | 2 protons and two neutrons 1 neutron (neutron is converted to proton and electron-electron emitted from nucleus is beta particle |
| Formulae for energy using planck's constant | E = hv E = hc/λ |
| 1 m is equivalent to ___ nm | 1 x 10^9 |
| What happens during Lyman series | Electron transition from higher energy levels to n=1 |
| What happens during Balmer series | Electron transition from higher energy levels to n=2 |
| What happens during Paschen series | Electron transition from higher energy levels to n=3 |
| What happens during Brackett series | Electron transition from higher energy levels to n=4 |
| What happens during Pfund series | Electron transition from higher energy levels to n=5 |
| Define orbital | The region where there is high probability of finding an electron |
| Define probability density | The probability of an electron being found at any distance from the nucleus |
| What are the four quantum numbers | Principal quantum number, n Angular quantum number, l Magnetic quantum numbers, m Spin quantum number, s |
| What does the principal quantum number do | Describes the energy level of the electron |
| What does the Angular quantum number do | Describes the shape of the orbital |
| What does the Magnetic quantum number do | Describes the # of orbitals within a sublevel |
| What does the spin quantum number do also state the principle that follows | Describes the spin of electron Pauli exclusion principle states that only 2 electrons can occupy any one orbit |
| State Aufbau Principle | Electrons are added one at a time starting with lowest energy orbital |
| Hund's rule | Electrons fill degenerate orbits one at a time with parallel spin before a second electron is added in the opposite spin |
| Why does 4s fill before 3d | 4s has a lower energy than 3d as such it will follow Aufbau principle and fill before 3d |
| Meaning of first ionization energy | The amount of energy required to remove one electron from one mole of an atom to form one mole of a gaseous ion with a single positive charge |
| Pauli exclusion principle | No more than two electrons can occupy an orbital |
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