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Give two properties of cathode rays. negatively charged (attracted to anode); negligible mass; straight-line motion; penetrating; cause fluorescence; move paddle wheel; deflected by electric and magnetic field; high-speed Define atomic number number of protons in the nucleus of an atom of the element What was the basis (periodic law) used by Mendeleev in arranging the elements in his periodic table? when arranged according to increasing atomic weight there is a periodic occurrence of elements with similar properties so that elements can be grouped by similar properties Why did Mendeleev leave spaces in his periodic table so that elements with same properties were in same group; because of undiscovered elements Explain why in a few instances Mendeleev reversed the order of elements required by his periodic law. to suit properties to groups; the lower atomic mass element fitted better in the higher group and vice versa; tellurium fitted better with the O group (Grp. VI); iodine fitted better with the halogens Explain why the alkali metals are all reactive readily lose a single electron from the outer shell; they have low first ionisation energy Explain why the reactivity of the alkali metals increases down the group. increase in atomic radius; outer electron getting further from nucleus; decrease in first ionisation energy; outer electron more easily lost Define atomic orbital region around the nucleus of an atom where there is a 99 % (high) probability of finding an electron; described by solution of Schrödinger equation Write the electron configuration (s, p, etc.) of the element manganese (Mn). 1s2 2s2 2p6 3s2 3p6 4s2 3d5 What do the electron configurations of the series of elements from scandium to zinc have in common? electrons entering (occupying) 3d sublevel Write the electron configuration (s, p, etc.) of the oxygen (oxide) ion (O2-). [1s2, 2s2, 2p6]2- State two differences between Mendeleev's periodic table and the modern periodic table of the elements. Mendeleev :Arranged in terms of atomic wgt. (mass) // reversed some pairs of elements // left gaps for undiscovered elements (in the table) // no noble gases // fewer elements //did not put transition elements (lanthanides, actinides) in separate block State two assumptions of Dalton's atomic theory of 1808. Small // indivisible // identical atomic mass (weight) for particular element Name the scientist who, about 1897, measured the ratio of charge to mass of the electron, e/m, Thomson Name the scientist who, about 1910, proved that the electrons in an atom reside in an electron cloud surrounding a smalldense positive central nucleus, Rutherford Name the scientist who, about 1911, measured the charge on the electron, e. Millikan Outline Bohr's atomic theory based on the hydrogen emission spectrum The electron in a hydrogen atom occupies fixed energy levels // an electron in an energy level does not radiate energy // electron occupies lowest energy levels available (ground state) // the electron can move to a higher energy level if it receives an amount of energy (photon of energy)(become excited) // the photon (energy) must be exactly equal to the energy difference between the ground state (a lower level) and a higher energy level (excited state) // the electron in an excited state (a higher level) is unstable // the excited electron falls back to a lower energy level // emitting the excess energy in the form of a photon of light (hf) / emitting light of a definite frequency (wavelength) / emitting light according to E2 - E1 = hf (hν) State two limitations of Bohr's theory that led to its modification Didn't work for higher elements / only worked for hydrogen / doesn't work for multi electron systems // Did not take wave-particle duality into account // Did not allow for uncertainty (probability) // Did not explain higher resolution spectra / didn't explain discovery of sublevels // Could not account for the existence of orbitals / Zeeman effect / splitting of spectral lines Draw the shape of the p-orbital. Dumbbell drawn State the maximum number of electrons that can be accommodated in a p-orbital two / 2 Define radioactivity Spontaneous random decay of a nucleus to release α, β or γ radiation Spontaneous random emission of radiation from unstable nuclei Define the half-life of a radioactive isotope Time taken for half of the radioactive isotopes (nuclei) in a sample to disintegrate (decay) time for sample to reach half its activity Determine the value of A and the value of Z in the following nuclear equation for the alpha decay of an americium-241 nucleus. 241 Am 95 to A Np Z + 4 He 2 + energy A = 237 // Z = 93 State one risk associated with exposure to alpha radiation. Causes ionisation / causes cancer / causes mutation Explain why the occupants of a house fitted with smoke detectors containing americium-241 are not at risk from alpha radiation emitted by these devices Radiation is not very penetrating Householders are advised to replace the batteries in smoke detectors regularly. Explain whether or not the americium-241 needs to be replaced regularly also Half life is over 400 years (very long) // sample does not deplete quickly Name the scientist who used charged oil drops to determinethe size of the charge on a sub-atomic particle, and the name sub-atomic particle involved in his experiments. Robert Millikan electron What change occurs in the nucleus of an atom when it undergoes beta emission? neutron changes to proton / number of neutrons decrease(s) by 1, number of protons increase(s) by 1 State the Heisenberg uncertainty principle not possible to measure the exact position (location) and momentum (energy, velocity) of electron in atom simultaneously (at same time) Define first ionisation energy of an element The minimum energy required to remove most loosely-bound (highest energy, outermost) electron from 1 mole of isolated (gaseous) atoms in their ground (lowest energy) state Use the values in the Mathematics Tables to plot a graph on graph paper of first ionisation energy versus atomic number for the elements with atomic numbers from 10 to 20 inclusive. axes correctly labeled // axes correctly scaled // points correctly plotted // graph correctly drawn Account fully for the general increase in ionisation energy values across the third period ofthe Periodic Table increased nuclear charge / increase in protons / increase in atomic number // decrease in atomic radius // no increase in shielding (screening) by inner shells Account fully for the peaks which occur in your graphat elements 12 and 15 increased stability of element 12 due to full outer sublevel (subshell) / stability due to electron being removed from full sublevel (subshell) increased stability of element15 due to half-full p sublevel (subshell) /stability due to three singly-occupied (half-full) p orbitals Account fully for the sharp decrease in ionisation energy value between elements 18 and 19 element 18 stable due to outer octet (eight in outer shell) / stable octet / noble gas config / outer sublevel (subshell) full / outer (electron being removed from) 3s2 3p6 element 19 has outer electron further from nucleus (in a new shell / more screened) / electron removed from next (4th) shell / electron removed from 4s - can only be given if full sp configuration of potassium is shown in candidate's work. Write the s, p electron configuration for the potassium atom. 1s2 2s2 2p6 3s2 3p6 4s1 / [Ar]4s1 state how many energy sub-levels are occupied by electrons in a potassium atom. 6 sublevels state how many (i) energy sub-levels, (ii) individual orbitals, are occupied by electrons in a potassium atom. 10 orbitals Explain why there are electrons in the fourth main energy level of potassium although the third main energy level is incomplete 4s sublevel (subshell) lower in energy than 3d What are isotopes? atoms of same element (same atomic number, same number of protons) having different mass numbers (different numbers of neutrons) What is the principle of the mass spectrometer positive ions are separated based on relative mass(es) (or charge-to-mass ratio) when moving in a magnetic field Calculate, to two decimal places, the relative atomic mass of a sample of neon shown by mass spectrometer to be composed of 90.50% of neon-20 and 9.50% of neon-22. 20.19 Write the electron configuration (s, p, etc.) of the aluminium ion (Al3+). [1s2 2s2 2p6]3+ What contribution did Henry Moseley make to the systematic arrangement of the elements in the periodic table? Identified the characteristic positive charge (or atomic number) for element and arranged elements in increasing atomic number Give two properties of alpha particles positive (+) charge (attracted to negative) // mass 4 // relatively low velocity (speed) // poor penetration (high absorption, stopped by skin, stopped by few sheet(s) of paper, stopped by few cm of air) // strong ionisation // stable nucleus // gains two electrons to form helium atom // damages cells (causes cancer) // deflected by electric fields // deflected by magnetic fields // causes luminescence(fluorescence, phosphorescence) Define energy level. discrete or fixed energy of electron in an atom / orbit (shell) in an atom which electrons of equal energy can occupy Distinguish between ground state and excited state for the electron in a hydrogen atom. ground: in lowest energy state / in n = 1 level (shell) / in 1s orbital excited: higher energy state / in n > 1 level (shell) / in orbital other than 1s Name the series of lines in the visible part of the line emission spectrum of hydrogen. Balmer series Explain how the expression E2 - E1 = hf links the occurrence of the visible lines in the hydrogen spectrum to energy levels in a hydrogen atom. E2 - E1: energy difference between higher and level 2 / energy emitted when electron falls from higher (e.g. E2) to lower (e.g. E1) // f : frequency of line in spectrum // each line produced is due to electrons falling from a particular higher level to a particular lower level // h is Planck's constant / hf is a photon // the expression indicates that the energy difference (E2 - E1) is proportional to the frequency (f) / the energy difference (E2 - E1) is a constant times the frequency (f) / Define atomic (covalent) radius half the distance between the centres of singly-bonded atoms of the same element Write the electron configuration (s, p) for the sulfur atom in its ground state, showing the arrangement in atomic orbitals of the highest energy electrons. 1s2 2s2 2p6 3s2 3p4 3px2 3py1 3pz1 State how many energy levels are occupied in a sulfur atom in its ground state. 3 State how many orbitals are occupied in a sulfur atomin its ground state. 9 Describe the model of atomic structure which existed immediately prior to Rutherford's gold foil experiment. A positively charged sphere with electrons embedded at random in it In Rutherford's gold foil experiment it was observed that most of the alpha particles went straight through the gold foil. Two other observations were made. State these other observations and explain how each helped Rutherford deduce that the atom has a nucleus There was deflection of alpha particles when they passed close to a small, positive mass (charge) Some alpha particles came straight back when they collided with a small, very dense mass which was called the nucleus Copy and complete the equation for the alpha-decay of polonium-210, filling in the values of x (atomic number), y (mass number) and Z (elemental symbol). 210Po 84 →y Z x + 4He2 210Po 84→206 Pb 82 + 4He2 Write the electron configuration (s, p, etc.) of a chromium atom in its ground state. 1s2 2s2 2p6 3s2 3p6 3d5 4s1 Name the scientist who identified cathode rays as subatomic particles. J J Thomson Give two differences between a nuclear reaction and a chemical reaction nuclear involves nucleus of atoms, chemical involves electron cloud // nuclear involves new elements being generated whereas chemical doesn't // nuclear involves large scale release of energy from nucleus whereas chemical may be ebndothermic or exothermic // involve the release of nuclear radiation (α, β or γ rays) // mass not conserved in nuclear reaction, but is conserved in a chemical reaction What contribution did Newlands make to the systematic arrangement of the elements known to him? Identified periodicity of properties and arranged elements in increasing rel. atomic mass in his law of octaves / Properties repeat every eighth (after seven) elements Describe how you would carry out a flame test on a sample of potassium chloride. Place sample of the salt on a wooden splint, soaked overnight in water and hold in the blue Bunsen flame, showing a lilac colour Why do different elements have unique atomic spectra? each element has a different distribution of energy levels (or different electron configuration) giving rise to different electron transitions What instrumental technique is based on the fact that each element has unique atomic spectra? atomic absorption spectrometry Define atomic orbital region around nucleus in which there is high probability of finding electron wave function of electron got by solution of Schrodinger's equation What does Heisenberg's uncertainty principle say about an electron in an atom? it is not possible to measure the exact position and energy (momentum, velocity) of an electron in an atom simultaneously Explain, in terms of the structures of the atoms, the trend in reactivity down Group I (the alkali metal group) of the periodic table. reactivity increases // increase in atomic radius // effective nuclear charge is the same ( screening effect of inner shells cancels the increase in nuclear charge) // outermost electron less tightly held by the nucleus What are isotopes? atoms of same element with the same atomic number, having different mass numbers because of different numbers of neutrons Define relative atomic mass, Ar. average mass of isotopes of an element taking abundances into account relative to 1/12 mass of carbon-12 atom What is the principle on which the mass spectrometer is based? positive ions are separated // based on relative mass(es) (charge/mass ratio) // when moving in a magnetic field Calculate the relative atomic mass of a sample of lithium, given that a mass spectrometer shows that it consists of 7.4 % of 6Li and 92.6 % of 7Li. 6.926 Name the series of coloured lines in the line emission spectrum of hydrogen corresponding to transitions of electrons from higher energy levels to the second (n = 2) energy level. Balmer What contribution did Dobereiner make to the systematic arrangement of the elements? he grouped elements of similar properties in groups of three (triads) where the mass of the middle element was the average of the other two. Distinguish between an atomic orbital and a sub-level. atomic orbitals are three dimensional spaces about the nucleus of an atom where there is a high probability of finding an electron whereas an atomic sub-level is a sub-division of a main energy level consisting of one or more orbitals of the same energy Name the scientist pictured on the right who is credited with the discovery in 1896 that uranium salts emit radiation. Becquerel Give an example of a radioactive isotope and state one common use made of this isotope. Deuterium, H-2; (nuclear fusion); carbon-13 (tracers in biosynthesis); carbon-14 (dating of ancient remains); caesium-135 (measurement of second); cobalt-60 (radiotherapy, cancer treatment, sterilisation); americium-241 (smoke alarms); phosphorus-32 (plant nutrient tracer, medical e.g. bone scans, radiotherapy); iodine-125 (medical tracer); caesium-137 (radiotherapy); oxygen-18 (reaction mechanisms); technetium-99 (medic-al tracer); uranium-235/uranium-238 (weapons, power); mass number essential] Describe and account for the trend in atomic radii of the elements across the second period decrease in atomic radius Because there is an increase in nuclear charge with constant screening effect (there is an increase in effective nuclear charge) Describe and account for the trend in atomic radii of the elements down any group increase in atomic radius Because there is an increase in the number of filled shells The minimum energy required to completely remove the most loosely bound electron from a mole of gaseous atoms in their ground state defines an important property of every element. Identify the energy quantity defined above first ionisation energy The minimum energy required to completely remove the most loosely bound electron from a mole of gaseous atoms in their ground state defines an important property of every element. State the unit used to measure this quantity. kilojoules per mole (kJ mol-1) Using X to represent an element, express the first ionisation energy in the form of a balanced chemical equation. X(g) ------ X+(g) + e- Would it take more or less energy to remove the most loosely bound electron from an atom if that electron were not in its ground state? Explain. less The electron already gained energy and is already raised to higher level further from nucleus An element has a low first ionisation energy value and a low electronegativity value. What does this information tell you about how reactive the element is likely to be, and what is likely to happen to the atoms of the element when they react? very reactive reacts by losing electron(s) Write the electron configuration (s, p, etc.) of the nitrogen atom. 1s2 2s2 2px1 2py1 2pz1 There is a general increase in first ionisation energy across a period of the periodic table. State the two principal reasons for this trend. increase in nuclear charge (atomic number) decrease in atomic radius Account for the decrease in first ionisation energy between nitrogen and oxygen. nitrogen has a stable electron configuration due to half-full p sublevel (subshell) oxygen has a less stable configuration due to 1s2 2s2 2p4 and is one electron away from a stable configuration Explain why the second ionisation energy of sodium is significantly (about nine times) higher than the first while the increase in the second ionisation energy of neon compared to its first is relatively small (less than twice the first). sodium: First electron removed from third shell whereas second removed from second shell loss of first gives high stability configuration with a full outer level (noble gas configuration), loss of second is from high stability configuration [from a new inner full level] Neon: first removed from full shell and second removed from same shell (both removed from 2p) Describe how Bohr used line emission spectra to explain the existence of energy levels in atoms. electrons in ground state are restricted to energy levels (energy of electron quantised) fixed energies (photons) absorbed and electrons jump to higher level(s) (excited state) energy only emitted (or absorbed) when electrons move between fixed levels excited state unstable, and electrons fall back to lower levels emitting energy as light energy difference between levels gives specific (definite) frequency (wavelength, line) of light in spectrum E2 - E1 = hν (hf) Why does each element have a unique line emission spectrum? each element has a different distribution of energy levels or different electron configurations, giving rise to different electron transitions The fact that each element has a unique line spectrum forms the basis for an instrumental technique which can be used to detect heavy metals and to measure their concentrations in a soil or a water sample. Name the instrumental technique. atomic absorption spectrometry (AAS) Bohr's atomic theory was later modified. Give one reason why this theory was updated. only worked for simple (hydrogen-like) atoms / wave nature of electron / Heisenberg uncertainty principle / discovery of sublevels / could not explain Zeeman effect / didn't explain splitting of lines Write an equation for the nuclear reaction involved in the beta decay of 14C (carbon-14). 14C6 ------ 0e-1 + 14N7 State two properties of beta (β) particles. negative charge / negligible mass / high speed / more penetrating than α (less penetrating than γ, stopped by 2 - 5 mm (sheet of) aluminium / less ionising than α (more ionising than γ) / damage body cells (cause cancer) / electrons from nucleus / deflected by electric fields / deflected by magnetic fields / fluorescence / phosphorescence Explain how the carbon-14 isotope allows certain archaeological discoveries to be dated. In living things, the ratio of carbon-12 to carbon-14 is constant After death, carbon-14 decays and the changed ratio and the half-life are used to find age (decrease in carbon-14 related to time passed since death) How many (i) electrons and (ii) neutrons has Cl- (mass number =37, atomic number =17)? 18 electrons 20 neutrons List the following three types of radiation in order of increasing penetrating power alpha- (α-) beta- (β-) gamma- (γ-) alpha, beta, gamma State two ways in which Mendeleev's periodic table of the elements differs from that of Moseley Mendeleev {Moseley}: order of atomic mass (weight) {order of atomic number} / gaps (fewer elements) {fewer gaps (no gaps), more elements } / reversed elements {no reversing} / man-made elements absent {man-made elements present} / transition elements not in separate block {transition elements in separate block} / lanthanides (rare earths) not in separate block {lanthanides in separate block} / actinides not in separate block {actinides in separate block} / no detectable naturally-occurring radioactive elements {detectable naturally-occurring radioactive elements present} Define energy level discrete (fixed) energy of electron in an atom/ an orbit in an atom that electrons of equal energy can occupy Define atomic orbital high probability region for electron / region in which electron is likely to be found Describe how the electrons are arranged in the orbitals of the highest occupied sub-level of a nitrogen atom in its ground state. one electron in each of the three p orbitals / 2px1 2py1 2pz1 What test could be carried out to distinguish between the sodium salts and the potassium salt flame test atomic absorption spectrometry (AAS) What observation would you make in a flame test on sodium and potassium salts sodium: yellow / orange potassium: lilac / violet Account for the general increase in ionisation energies across elements 3 to 10 increase in nuclear charge decrease in atomic radius Explain why the ionisation energies of element number 4 and 7 are exceptionally high relative to the general trend across period 2 Element 4: outer sublevel full / 1s2 2s2 / electron from full 2s sublevel giving increased stability Element 7: half-full p sublevel / 1s2 2s2 2p3 / giving increased stability How does the definition of second ionisation energy differ from that of first ionisation energy? electron removed from monopositive ion / X+ ------ X2+ + e- What are isotopes atoms of same element with the same atomic number, having different mass numbers because of different numbers of neutrons Write the electronic configuration of a neutral copper atom 1s2 2s2 2p6 3s2 3p6 3d10 4s1 What spectroscopic technique is used to detect heavy metals, e.g. lead, in environmental analysis atomic absorption spectrometry / AAS Account for the trend in first ionisation energies of the elements going down Group II of the periodic table, i.e. the alkaline-earth metals. decrease due to increasing atomic radius increased shielding (screening) offsets increased nuclear charge / Explain why there is an increase in the first eight ionisation energies of magnesium increasing positive charge of species losing electron (no. of protons same but no. of electrons decreasing) decreasing radius Account fully for the trends in first ionisation energies of elements across the second period of the periodic table (i.e. Li to Ne). increasing nuclear charge decreasing atomic radius DROPS: Be or N stable Be due to 2s full / 1s2 2s2 N due to half-full p sublevel / 1s2 2s2 2p3 B or O unstable B due to one electron in 2p / 1s2 2s2 2p1 / one electron away from stable / O due to 1s2 2s2 2p4 / one electron away from stable configuration/ Account for the dramatic increase in ionisation energy of magnesium going from the second to the third ionisation. third electron coming from new full shell (2s2 2p6) with a high stability configuration (noble gas (neon) configuration) Between which two ionisations would you expect the next dramatic increase (after the third ionisation energy) to occur if the data for further ionisation energies of magnesium were examined? Give a reason for your answer. between 10th and 11th REASON: eleventh electron coming from new full shell with a high stability configuration (noble gas (helium) configuration) Mass spectrometry is a widely used instrumental technique in chemistry. Give one application of this technique. separating isotopes / measuring relative atomic mass / measuring relative molecular mass / determining structure / identifying species / measuring relative abundance / analysing waste gases (from cars, dumps, etc.) / water analysis / drug metabolites / quality control / environmental analysis What are the main principles on which mass spectrometry is based? charged particles moving in a magnetic field experience a force and are deflected in a circular path according to their mass/charge ratio What are the fundamental processes that occur in a mass spectrometer? vaporisation of sample ionisation to positive ions acceleration in electric field separation in magnetic field by mass detection producing a mass spectrum What is the colour of the light associated with the line emission spectrum of sodium? yellow / orange Explain how line emission spectra occur. electrons are restricted to discrete energy levels they jump to higher levels when they absorb enough energy fall back emitting energy as light energy difference between levels gives specific (definite) frequency (wavelength, line) of light in spectrum. E2 - E1 = hv (hf) What evidence do line emission spectra provide for the existence of energy levels in atoms? only fixed (specific) frequencies are emitted therefore electrons must be restricted to certain discrete energy values Bohr's energy levels gave same results as those from spectra by Balmer and Rydberg Why is it possible for line emission spectra to be used to distinguish between different elements? different elements have different unique spectra because of different distribution of energy levels What are alpha-particles (α-particles)? helium nuclei two protons and two neutrons Describe the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus He bombarded gold foil (leaf) with a-particles used zinc sulfide detector (phosphorescent screen) for scattered a-particles most passed straight through / some deflected at large angles / a small number reflected (bounced back) Explain how Rutherford interpreted the results of his gold foil experiment to conclude that the atom has a nucleus The only possible explanations for the observations are: mass concentrated (contained in small space) / positive charge concentrated (contained in small space) / atom is mostly empty space How many (i) protons, (ii) neutrons are there in the selenium atom 79Se34 34 protons 45 neutrons What is the name given to the energy change corresponding to the reaction represented by the equation: X(g) → X+(g) + e- First ionisation energy Explain why atomic radius decreases going from aluminium to chlorine increased nuclear charge electrons going into the same energy level Explain why atomic radius increases going from nitrogen to phosphorus extra shell of electrons Explain why the atomic radii of chromium, copper and zinc are very similar all d-blobk elements and electrons go into the inner d sublevel there is no change in effective nuclear charge Write the electronic configurations (s, p, etc.) for chromium and copper and explain why these two elements are exceptions to the normal order in which electrons occupy sublevels. Cr 1s2 2s2 2p6 3s2 3p6 4s1 3d5 Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10 normal order is 4s before 3d, but half-filled or filled sublevels give extra stability Chromium, copper and zinc are all classified as d-block elements but only chromium and copper are classified as transition elements. Explain why this is the case. Cr and Cu have ions with partially filled d sublevels, the ions of Zn have filled d sublevel Cr and Cu show variable valency, Zn has fixed valency Cr and Cu formed coloured compounds, Zn doesn't