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How do you know how many atoms and how many elements are in a symbol equation?
CO2 Tells you how many ELEMENTS there are (an easy way to do this is to count the capital letters) The number tells you how many ATOMS of each of that element there is
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Have a go… How many atoms and elements are in... H2O CaCO3 2MgO 2CaCl2
Mg(NO3) 2 Everything is multiplied by this number Everything in the bracket is multiplied by this number
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Filtration - separates fine, insoluble particles from a liquid
Fractional distillation – separates liquids with different boiling points Condenser Filter paper Funnel Conical flask Filtration - separates fine, insoluble particles from a liquid Chromatography – separates a mixture of chemicals / dyes Evaporating dish Bunsen burner Tripod Gauze Fractional distillation – separates liquids with different boiling points Evaporation / crystallisation – separates liquid from a dissolved substance
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Order of discovery of sub atomic particles
Date Scientist Electron 1897 JJ Thomson Proton 1919 Ernest Rutherford Neutron 1932 James Chadwick
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Rutherford Experiment: the set up
Geiger and Marsden counted the tiny green flashes in the microscope produced when alpha particles hit the screen. Both Geiger and Marsden described this as one of the most difficult and boring experiments they’d ever had to do. Moveable Microscope Zinc sulphide screen (glows when hit by alpha particles) Shield Source of alpha particles Vacuum (air pumped out) Very thin gold foil
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Geiger and Marsden placed the microscope as shown.
As expected, most of the alpha particles went straight through A few alpha particles were scattered by angles less than 90º, also as expected.
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Much to their surprise, a very small number of alpha particles (about 1 in 8000) bounced off the gold atoms! Under protest, Geiger and Marsden placed the microscope behind the gold leaf. They handed the results to Professor Rutherford who now had to explain what was going on.
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Observations Rutherford’s experiment finished with 3 observations. You need to explain what each observation tells us about the atom as we know it today Most of the fast, highly charged alpha particles went whizzing straight through un-deflected. Some of the alpha particles were deflected through a small angles A very small number of alpha particles were deflected backwards!
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SUGGESTS THAT MOST OF THE ATOM IS EMPTY SPACE!!
Conclusions Most of the fast, highly charged alpha particles went whizzing straight through undeflected. SUGGESTS THAT MOST OF THE ATOM IS EMPTY SPACE!!
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Some of the alpha particles were deflected through a small angles!
Conclusions Some of the alpha particles were deflected through a small angles! SUGGESTS THAT THERE IS A CONCENTRATED POSITIVE MASS SOMEWHERE IN THE ATOM.
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A very small number of alpha particles were deflected backwards!
Conclusions A very small number of alpha particles were deflected backwards! SUGGESTS THAT THE CONCENTRATED MASS IS MINISCULE COMPARED TO THE SIZE OF THE REST OF THE ATOM, BUT CONTAINS MOST OF THE MASS
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What did Bohr do? (1913) Realised that electrons should be attracted in to the nucleus Used mathematical models to show that electrons occupy fixed energy levels (or shells) around the nucleus
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Think about the location of:
Plum Pudding Model Nuclear Model Compare the differences between the plum pudding model and the nuclear model. Think about the location of: The mass The negative charge The positive charge The density
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The atom nucleus electron neutron
Draw a labelled diagram of the atom showing the nucleus and labelling protons, neutrons and electrons. The overall charge on an atom is 0… what does this tell you about the number of protons and electrons? nucleus electron Sub atomic particle Relative charge Relative Mass Proton Neutron Electron proton neutron +1 1 1 -1 1/2000 (Very small)
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How big is an atom? Atoms are very small, having a radius of about 0.1 nm (1 x m) The radius of a nucleus is less than 1/ of that of the atom (about 1 x m)
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What does this show you? 12 C 6 Atomic Mass number Carbon
(show the number of protons and neutrons in the nucleus) (number of neutrons = top number – bottom number) 12 C 6 Carbon Atomic number (tells you the number of protons and the number of electrons) How do we calculate mass and atomic numbers?
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H H H Isotopes 1 2 1 3 1 Hydrogen Deuterium Tritium
Isotopes are atoms of the same element (same protons & electrons) with different numbers of neutrons. This makes them unstable. Hydrogen Deuterium Tritium H 1 H 2 1 H 3 1
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Isotopes and RAM Many elements are a mixture of isotopes. The RAM given in the periodic table takes account of this. To calculate the RAM of a mixture of isotopes, multiply the percentage of each isotope by its atomic mass and add them together. For example, chlorine exists as two isotopes: chlorine-35 (75%) and chlorine-37 (25%). = (0.75 x 35) + (0.25 x 37) = = 35.5 RAM of chlorine = (75% x 35) + (25% x 37)
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Electronic structure Chlorine Calcium Argon 2,8,7 2,8,8,2 2,8,8 xx xx
Cl xx xx x xx xx Ca xx xx x x x xx xx x x xx 2,8,7 2,8,8,2 2,8,8 Only a certain number of electrons can fit in each ‘shell’. 2 in the first shell 8 in the second shell 8 in the third shell
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Group number = how many electrons in the outer shell
Alkali Metals Nobel gases Period number = how many shells the atom has Halogens Transition Metals
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Development of the Periodic table
John Newlands (1865) – Arranged elements in order of atomic weights (realised every 8th element had the same properties) Didn’t leave gaps so only really worked up until calcium Had lots more dissimilar elements in a column Dmitri Mendeleev (1869) – Left gaps for undiscovered elements Changed the order of some elements so they fit with the properties Elements with the predicted properties eventually discovered
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What is an ION? An ION is a ‘charged’ particle.
Video An ION is a ‘charged’ particle. Atoms 'like' to have a full shell of electrons. They are more stable if they have a full electron shell. Atoms will lose or gain electrons in order to gain a full shell. It has therefore either LOST or GAINED electrons.
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Click on me!! Remember that the proton number tells you how many protons or electrons the atom has. Not any more!!! Why not??
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An ion is shown like this to show the electron shells
Or simply like this
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The sodium ion + Sodium atom: Sodium ion: 11 protons = +11
11 electrons = -11 10 electrons = -10 Total charge = 0 Total charge = +1 Na + Na one electron is lost Electron arrangement: (partially full outer shell) Electron arrangement: [2.8]+ (full outer shell)
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The magnesium ion 2+ Magnesium atom: Magnesium ion: 12 protons = +12
12 electrons = -12 10 electrons = -10 Total charge = 0 Total charge = +2 Mg 2+ Mg two electrons are lost Electron arrangement: (partially full outer shell) Electron arrangement: [2.8]2+ (full outer shell)
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Negative ions An atom that gains one or more electrons forms a negative ion. Non-metal atoms, such as chlorine, oxygen and nitrogen, form positive ions. Negative ions have a small ‘-’ symbol and a number by them to indicate how many electrons they have gained to fill their outer shell. For example: chloride ion = Cl- (not Cl1-) chlorine atom = oxygen atom = 2.6 oxide ion = O2- nitrogen atom = 2.5 nitride ion = N3- The name of the ion is slightly different to that of the atom – it ends ‘–ide’.
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The fluoride ion - Fluorine atom: Fluoride ion: 9 protons = +9
9 electrons = -9 10 electrons = -10 Total charge = 0 Total charge = - 1 - F F one electron is gained Electron arrangement: 2.7 (partially full outer shell) Electron arrangement: [2.8]- (full outer shell)
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two electrons are gained
The sulfide ion Sulfur atom: Sulfide ion: 16 protons = +16 16 protons = +16 16 electrons = -16 18 electrons = -18 Total charge = 0 Total charge = 2- S S two electrons are gained Electron arrangement: (partially full outer shell) Electron arrangement: [2.8.8]2- (full outer shell)
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AN ATOM WITH A POSITIVE OR NEGATIVE CHARGE IS CALLED AN ION!!!!
Loss/gain of electrons Charge of stable ion Li F Mg Cl O Al Complete the table to show how each of the following atoms can become stable and what will be the charge on the ion?
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Group 0
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Group 1 (alkali) metals More reactive Higher melting point
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Metals and oxygen – general equation
Potassium and sodium are metals that react vigorously with water even when a small amount of each metal is used. metal oxygen metal oxide Lithium + oxygen Lithium oxide Li O2 Li2O Sodium + oxygen ________ _______ Na O2 Na2O Potassium + oxygen ________ ______ K O2 K2O
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Metals and chlorine – general equation
Potassium and sodium are metals that react vigorously with chlorine even when a small amount of each metal is used. metal chlorine metal chloride Lithium + chlorine Lithium chloride 2Li Cl2 LiCl Sodium + chlorine ________ _______ 2Na Cl2 NaCl Potassium + chlorine ________ ______ 2K Cl2 KCl
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Metals and water – general equation
Potassium and sodium are metals that react vigorously with water even when a small amount of each metal is used. metal water metal hydroxide hydrogen Lithium + Water Lithium Hydroxide + Hydrogen 2Li + 2H2O 2LiOH + H2 Sodium + Water ________ _______ + Hydrogen 2Na + 2H2O 2NaOH + H2 Potassium + Water ________ ______ + _______ 2K + 2H2O 2KOH + H2
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Halogens Less reactive
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Halogen displacement A more reactive halogen will displace and less reactive halogen from an aqueous solution of it’s salt 2KCl + I2 2KBr + I2 halogen chlorine bromine iodine salt (aq) potassium chloride potassium iodide potassium bromide 2KCl + Br2 no reaction
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Displacement Equations
Potassium Bromide and Chlorine: 2KBr + Cl2 2KCl + Br2 Potassium Iodide and Chlorine: 2KI + Cl2 2KCl + I2 Potassium Iodide and Bromine: 2KI + Br2 2KBr + I2
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Electron shielding Reasons why reactivity increases when you go down group 1, but decreases when you go down group 7. Electrons are further away from the nucleus Less attraction to the nucleus the further away the electrons are Makes it easier to lose electrons if they are further away but harder to gain Electrons between the nucleus repel other electrons
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Physical properties of transition metals
They are good conductors of electricity and thermal energy They are hard and strong The have high densities They have high melting points (with the exception of mercury which is a liquid at room temperature) Transition metals have very high melting points compared with group 1 metals
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Chemical properties of transition metals
Don’t react as strongly with oxygen, chlorine or water as the alkali metals do. Most transition metals react very slowly with oxygen and water (e.g iron rusts very slowly over time) Transition metals are much less reactive compared with group 1 metals
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Compounds of transition elements
Transition elements form coloured compounds: Copper (II) sulfate is blue Nickel (II) carbonate pale green Chromium (III) oxide is dark green Manganese(II) chloride is pale pink Transition metals can usually form more than one ion
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