# Atomic Structure. Name Mass Charge Location Protons 1 +1 Nucleus Neutrons 1 0 Nucleus Electrons 1/ Orbit nucleus in outer shells

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1 Atomic Structure called nucleons Name Mass Charge Location Protons 1 +1 Nucleus Neutrons 1 0 Nucleus Electrons 1/ Orbit nucleus in outer shells The number of protons equals the atomic number This is the number which defines the element (ie all elements have different atomic numbers) The atomic number can be written as a subscript (below the line) in front of the symbol (eg 6 C) In a neutral atom, the number of electrons equals the number of protons The mass number is equal to the number of nucleons The mass number can be written as a superscript before the symbol (eg 12 C) Isotopes are when a single element has atoms with the same number of protons, but different number of neutrons (and therefore mass number) Example: Chlorine comes in two different forms One form has a mass number of 35 and the other has a mass number of 37: 35 Cl - 17 protons 18 neutrons 37 Cl - 17 protons 20 neutrons Relative atomic mass (A r ) this is the mass of an average atom of an element divided by one atom of 1 H The A r takes into account the relative abundance of the naturally occurring isotopes of the element ok, so basically, you find the average of the masses of the different isotopes! The mass number is always an integer (that s a whole number for all you non-mathematicians) BUT the A r does not have to be Example: What is the Ar of chlorine given that there are two isotopes: 35 Cl (which is 75% abundant) and 37 Cl (which is 25% abundant)? To do this, we need to look at the abundance to work out the mass of an average atom of Cl As 35 Cl is 75% abundant, we multiply 35 by 75% (ie 075) and as 37 Cl is 25% abundant, we multiply 37 by 25% (ie 025) The two numbers are then added together and divided by the mass of one atom of 1 H (ie 1 so this step is pointless ): (35 075) + (37 025) = 355 (If you didn t understand that don t worry, here s an easier way just for you simply remember this formula: the sum of: mass abundance (for all the isotopes)

2 The Periodic Table There are approximately 100 elements Everything is made up of one or more elements The periodic table shows elements in increasing atomic number Electrons are accommodated in shells The maximum in the first shell is 2, the maximum in the second shell is 8 and the maximum in the third shell is also 8 Electrons always fill lower energy shells (ie closer to the nucleus) first 1 st electron shell (can hold up to 2 electrons) 2 nd electron shell (can hold up to 8 electrons) nucleus with protons and neutrons The first 20 elements: Atomic Number Symbol Element Shell 1 Shell 2 Shell 3 Shell 4 1 H Hydrogen 1 2 He Helium 2 3 Li Lithium Be Berillium B Boron C Carbon N Nitrogen O Oxygen F Fluorine Ne Neon Na Sodium Mg Magnesium Al Aluminium Si Silicon P Phosphorous S Sulphur Cl Chlorine Ar Argon K Potassium Ca Calcium Other important elements include: Atomic number Symbol Element 26 Fe Iron 29 Cu Copper 30 Zn Zinc 35 Br Bromine Atomic number Symbol Element 47 Ag Silver 53 I Iodine 56 Ba Barium 82 Pb Lead

3 In the periodic table, elements are arranged in rows named periods when a single electron shell is filling We start a new period when we start filling the next electron shell At the top of each column or group, there is a number showing how many electrons are in the outer shell (eg group 7 has 7 electrons in the outer shell) Element An element is a pure substance which cannot be broken down any simpler by chemical means Atoms of the same element have the same atomic number A sample of an element may be made up of atoms or molecules Compound Compounds are pure substances containing two or more elements chemically bonded together in fixed proportions by mass Example: H 2 O 2g Hydrogen, 16g oxygen 1g Hydrogen, 8g oxygen The properties of a compound are different to those of its constituent element The chemical bonds in compounds are either ionic or covalent (we will look at this a bit later fun fun fun!) Compounds can be either ions or molecules Mixtures Vary in composition and can be physically separated Mixtures and Compounds the difference! Iron and sulphur mixed together looks like yellow powder with grey bits in it (a mixture) You can separate then by: - using a magnet (the smart way of getting a needle from a haystack!) - dissolving the sulphur in a solvent (eg toluene) and filtering when hot Then let the solution cool and the sulphur crystallises If the mixture is heated, an exothermic reaction (a reaction that gives out heat) takes place There are 3 things to prove that a reaction has taken place: 1 It continues to glow red hot even when you stop heating it 2 The product is a brittle grey solid, which does not look like the mixture 3 The mixture reacts with dilute hydrochloric acid to produce hydrogen whereas the compound (after heating) reacts with hydrochloric acid to make foul smelling hydrogen sulphide Iron (s) + Sulphur (l) Iron (II) Sulphide (s) Fe (s) + S (l) FeS (s) Atoms of different elements can combine to form compounds by the formation of new chemical bonds Magnesium (s) + Oxygen (g) Magnesium Oxide (s) 2Mg (s) + O 2 (g) 2MgO (s)

4 Ions Ions are formed from atoms by the gain or loss of electrons The nucleus is left unaffected The maximum that can be lost or gained is 3 Generally we form an ion which has a noble gas configuration (ie all full outer shells) Positive ions are called cations Negative ions are called anions Atoms of elements in group 1 LOSE one electron to form a 1+ ion of noble gas Na Na + + 1e (electron) 2, 8, 1 2, 8 (same electron configuration as neon) Atoms of elements in group 2 LOSE two electrons to form a 2+ ion of noble gas Ca Ca e (electrons) 2, 8, 8, 2 2, 8 (same electron configuration as argon) Atoms of elements in group 3 LOSE three electrons to form a 3+ ion of noble gas Al Al e (electrons) 2, 8, 3 2, 8 (same electron configuration as neon) Atoms of elements in group 7 GAIN one electron to form a 1 ion of noble gas (electron) e + Cl Cl 2, 8, 7 2, 8, 8 (same electron configuration as argon) Atoms of elements in group 6 GAIN two electrons to form a 2 ion of noble gas (electrons) 2e + O O 2 2, 6 2, 8 (same electron configuration as neon)

5 Formulae of Ionic compounds The ones in red / green need to be learnt, the rest can be worked out by looking at their position in the periodic table Mg 2+ O 2 (oxygen) F (fluoride) Li + (lithium) (magnesium) S 2 (sulphide) Cl (chloride) Na + (sodium) Ca 2+ (calcium) Br (bromide) K + (potassium) Ba 2+ (barium) I (iodide) Ag + (silver) Zn 2+ (zinc) H + (hydrogen) Pb 2+ (lead) Cu + (copper I) Cu 2+ (copper II) Fe 2+ (iron II) SO 2 4 (sulphate) CO 2 3 (carbonate) SO 3 2 (sulphite) OH (hydroxide) NO 3 (nitrate) HCO 3 (hydrogencarbonate) CH 3 CO 2 (ethanoate) NH 4 + (ammonium) Al 3+ (aluminium III) Fe 3+ (iron III) Radical Ions (2 or more atoms covalently bonded together carrying a charge they behave as a single unit) Both copper and iron can form ions of more than one charge We have to write the charge in roman numerals in the name to distinguish between the compounds Cu 2 O = Copper (I) oxide CuO = Copper (II) oxide FeCl 2 = FeCl 3 = Iron (II) chloride Iron (III) chloride Learning how to write formulae is VERY important lots of chemistry is about formulae Basically, all you have to do is take the symbol of each element and put it together making sure that the charges cancel out and that you put the positive ion first So three steps: 1 In name and formulae, the positive ion goes first 2 The total charge must equal 0 3 If you have to multiply a radical ion, put it in brackets Examples: Sodium Chloride (Na + and Cl ) NaCl Calcium Chloride (Ca 2+ and Cl ) CaCl 2 (notice that 2 Cls are needed to cancel the 2+ of the Ca) Calcium Nitrate (Ca 2+ and NO 3 ) Ca(NO 3 ) 2 Try some for yourself (just to see if you really understood it and aren t just pretending to): 1 Sodium sulphate 2 Aluminium chloride 3 Calcium sulphide 4 Aluminium nitrate 5 Sodium nitrate 6 Ammonium chloride 7 Ammonium sulphide 8 Aluminium sulphide

6 A GCSE Chemistry word-fill worksheet on "ATOMIC STRUCTURE, ISOTOPES and ELECTRON STRUCTURE" nd th 5 5th atomic atomic electrons electrons electrons group iron isotopes mass mass neutrons neutrons nucleus number period shell shells three Q1(a) Atoms are made of fundamental particles called protons (+), (0) and (-) (b) The centre of the atom is called the (c) It consists of protons and and contains most of the mass of the atom Q2(a) The number of protons in the atom is called the number It also equals the number of atom (b) The the nucleus in a neutral is the sum of the protons and neutrons in Q3 An atom of mass number 43, and atomic number 21, consists of protons, neutrons and electrons Q4 (a) In the symbol for an atom of shown on the left, the atom consists of protons, neutrons and electrons (b) Atoms of the same element with a different number due to different numbers of neutrons are called Q5(a) Electrons are arranged around the nucleus in energy levels or (b) The 1st shell can have a maximum of electrons, the shell a maximum of electrons and the 3rd shell a maximum of electrons (c) The 19th and 20th electrons go in the shell (d) The electron arrangement, showing the number of electrons in each can be written out in shorthand eg 286 for the 1st, 2nd and 3rd shells respectively

7 Q6(a) Apart from hydrogen and helium in period 1 of the Periodic Table the last number in the arrangement is equal to the number in the Periodic Table (b) The number of shells used containing electrons is equal to the of electrons in an atom is equal to the number (c) The number or proton number Q7(a) Phosphorus has an atomic number of 15 so the atoms have protons or 15 (b) The electron arrangement will be (c) In the Periodic Table it will be a member of Group and it will be the element along Period Q8(a) Fluorine has an atomic number of so the atoms have 9 protons or electrons (b) Its electron arrangement is and it belongs to Group on Period

8 Ionic Equations Questions (A) Translate into symbols and balance each equation: 1 calcium carbonate breaks down on heating to give calcium oxide and carbon dioxide 2 sulphur burns in oxygen to form sulphur dioxide gas 3 heating magnesium and sulphur powders together produces solid magnesium sulphide 4 sodium hydroxide and hydrochloric acid react to form sodium chloride and water 5 hydrogen gas and oxygen gas burn together to form water 6 zinc metal and copper sulphate solution react to produce copper and zinc sulphate solution (B) Balance these equations and add state symbols: 1 CuO + HNO3 to Cu(NO3)2 + H2O 2 Al + Cl2 to AlCl3 3 N2 + H2 to NH3 4 Na + H2O to NaOH + H2 5 K2CO3 + H2SO4 to K2SO4 + H2O + CO2 6 Fe + H2SO4 to FeSO4 + H2 7 CH4 + O2 to CO2 + H2O 8 Pb(NO3)2 + NaCl to PbCl2 + NaNO3 (C) Balance these equations: 1 MnO2 + HCl to MnCl2 + Cl2 + H2O 2 HBr + H2SO4 to SO2 + Br2 + H2O 3 HI + H2SO4 to I2 + H2S + H2O 4 KMnO4 + HCl to KCl + MnCL2 + Cl2 + H2O 5 FeSO4 + KMnO4 + H2SO4 to (Fe)2 (SO4)3+K2SO4+MnSO4+H2O

9 Equation Answers A 1 CaCO3(s) CaO(s) + CO2(g) 2 S(s) + O2(g) SO2(g) 3 Mg(s) + S(s) MgS(s) 4 NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) 5 2H2(g) + O2(g) 2H2O(l) 6 Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s) B 1 CuO(s) + 2HNO3(aq) Cu(NO3)2(aq) + H2O(l) 2 2Al(s) + 3Cl2(g) 2AlCl3(s) 3 N2(g) + 3H2(g) 2NH3(g) 4 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) 5 K2CO3(s) + H2SO4(aq) K2SO4(aq) + H2O(l) + CO2(g) 6 Fe(s) + H2SO4(aq) FeSO4(aq) + H2(g) 7 CH4(g) + 2O2(g) CO2(g) + 2H2O(g) 8 Pb(NO3)2(aq) + 2NaCl(aq) PbCl2(s) + 2NaNO3(aq) C 1 MnO2 + 4HCl MnCl2 + Cl2 + 2H2O 2 2HBr + H2SO4 SO2 + Br2 + 2H2O 3 8HI + H2SO4 4I2 + H2S + 4H2O 4 2KMnO4 + 16HCl 2KCl + 2MnCl2 + 5Cl2 + 8H2O 5 10FeSO4 + 2KMnO4 + 5(Fe)2(SO4)3 + K2SO4 + 2MnSO4 + 8H2SO4 8H2O

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