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Note On Atomic Structure

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Published in: Chemistry
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This is topic 1 atomic structure

Alaa N / Abu Dhabi

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Qualification: Bs.c clinical pharmacist

Teaches: Biology, Chemistry

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  1. CHEMISTRY 0971 Topic 1 Atomic Structure
  2. CHEMISTRY 0971 ATOMIC STRUCTURE 6 Atom: is the smallest uncharged particle that can take part in a chemical change. -At the center Of the atom there is a tiny nucleus . -The nucleus is made up of protons and neutrons -The electrons spin around in areas called electrons shells or energy levels . -Protons , neutrons and electrons are called subatomic particles -Electrons are held within the atom by an electrostatic force of attraction between the negative electrons and the positive charge of protons in the nucleus. POC Subatomic particle Protons Neutrons Electrons RELATIVE CHARGE The centre is called the nys!eys RELATIVE MASS 1 1 1/1840 electron shell LOCATION IN ATOM In nucleus Electronic shells -Protons and neutrons have the same mass , while electrons are much smaller (virtually no mass) -All Atoms are neutral , why ? Because they contain equal number of protons and electrons
  3. CHEMISTRY 0971 THE BASIS OF THE PERIODIC. TABLE 6 -The-proton-number-or-atomjc-numbecdecides the atom belongs to which element I.e. It is unique for each element. -The periodic table is arranged in order of proton number . -Each element in the periodic table is represented as follow: z A : The Mass number or Nucleon number (neutrons + protons) Z :The proton number or atomic number X : Is the symbol of the element The number of neutrons: nucleon number — proton number The number of electrons is equal to the number of protons 16 o 8 Oxygen- 16 has 8 Protons 8 Electrons 16-8=8 Neutrons The nucleon number or mass number: is the number of protons and neutrons in the nucleus of an atom The proton number or atomic number : is the number of protons in the nucleus of an atom 4
  4. CHEMISTRY Complete the table 6 Element Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Symbol No. of protons No. of neutrons Be o No. of electrons
  5. CHEMISTRY 0971 The periodic table gives us 2 information about the electronic configuration: 1- for the main group elements, The group 6 number is equal to the number of electrons in outer shell 2- The period number is equal to the number of shells Complete the table Groups or Fami lies ( vert'c•l columns) Periods or Series (honzont.l rows) Element Hydrogen Helium Lithium Beryllium Boron Carbon Symbol He c Electronic configuration 7
  6. CHEMISTRY 0971 ELECTRONIC CONFIGURAT(ON It is the arrangement of electrons in an atom Electrons are in orbit around the central nucleus of the atom The electron orbits are called shells (or energy levels) 6 The shells are filled starting with the lowest energy shell (the closest shell to the nucleus) The first shell can hold up to 2 electrons The second shell can contain a maximum of 8 electrons The third shell can contain up to 8 or 18 electrons second enero leva Lithium atom electrons first energy level nucleus. containing 3 tons and 4 neutrons Instead of drawing the shells you can give the electron arrangement or electronic structure in terms of number (1st shell, 2nd shell , 3rd shell) AAXPLE 2,1 for lithium 2,8,1 for sodium The significance of the noble gas electronic structures -Group O elements, the noble gases , have a Full outer shell of electrons. This type of Electronic structure is very stable- so the atoms cannot gain or lose electrons . This makes the noble gases unreactive. -Exist naturally as single atoms -When atoms of other elements combine, The compounds formed have noble gas electronic configuration of full electron shells around each atom in the molecules of the compound 6
  7. CHEMISTRY Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine 6 o Na Mg Al s ISOTOPES Isotopes are atoms of the same element having the same number of protons (atomic number) but different nucleon number due to difference in number of neutrons.
  8. CHEMISTRY Give reason Isotopes are of the same element Isotopes have the same chemical properties Isotopes have different physical properties V Gomplete@he-table 6 Because they have same number of protons Because they have the same number of electrons in their outer shell (electronic structure) Because the mass of the atoms will differ and therefore other properties like density and rate of diffusion Electrons Neutrons Carbon Hydrogen Protons c c c Hydrogen deuterüJm Tritium
  9. CHEMISTRY 0971 RELATIVE ATOMIC MASS (AR) How the mass of the atom is measured ? 6 The mass Of the atom cannot be weighed on a balance but it's mass can be compared to another atom (Carbon-12 ) using mass spectrometer . Since we are comparing the masses of the atoms , the values we obtain are relative values Relative atomic mass(hr)_: the average mass of the isotopes of an element compared to 1/12 of the mass of carbon-12 Most elements exists naturally as a mixture of isotopes. Therefore the value we use for the atomic mass of an element is the average mass. For example : Chlorine exists in nature as two different isotopes CI-35 (75%) and Cl-37 (25%) How to calculate the relative atomic mass ? MASS no. X PERCENTAGE 100 SO for chlorine the relative atomic mass will be calculated as follow: (35 (37 x E) -35.5 100 100 10
  10. CHEMISTRY Calculate the relative atomic mass of the following elements from their abundance 6 Element Isotopes Lithium Li-7 Mg-24 Mg-25 Magnesium Mg-26 abundance Relative atomic mass 7.5% 92.5% 78.6% 10.1% 11.3% RADIOACTIVE ISOTOPES They are isotopes which have unstable nuclei that emit radiation in order to be more stable
  11. 6 CHEMISTRY ELEMENTS . COMPOUNDS AND MIXTURES Substances are either Pure Element : Pure substance made up of one type of Or pure substance which cannot be broken down into anything simpler by chemical reaction Helium (Exist as atoms) Compound: Bromine (Exist as molecules) Pure substance made up of two or more elements chemically combined together (Chemically bonded together) Impure Mixture: substance made up of two or more elements NOT chemically combined together Air (Consist of 02 and N2 molecules ,argon atoms , C02 molecules ) E.g. Water (Exist as molecules made up Of 2 different elements) 12
  12. CHEMISTRY Compound Made up of one substance Composition is always the same 6 Mixture Made up of 2 or more substances Composition may vary Broken by chemical reactions Substances can be separated by physical methods ATOM Vs ION Atom Smallest uncharged particle Equal number of protons and electrons Ion . Smallest charged particle Unequal number of protons and electrons -positive ion = more protons than electrons -Negative ion more electrons than protons nunt•er of protons 6 12 13 8 11 nurtt>er of neutrons 8 12 14 8 12 number of -Particle A B and E are atoms electrons 6 12 10 10 11 as they have equal number Of protons and electrons -Particle C is a positive ion as it has 3 more protons than electrons -Particle D is a negative ion as it has 2 more electrons than protons 13

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