Periodic Trends


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Periodic Trends

  1. 1. Periodic Trends Chapter 6 Section 3 pp.163-169
  2. 2. What is a trend? <ul><li>1. The general direction in which something tends to move. </li></ul><ul><li>2. A general tendency or inclination. See Synonyms at tendency . </li></ul>
  3. 3. Things to remember… <ul><li>Nuclear charge </li></ul><ul><ul><li>Positively charged nucleus pulls electrons towards it </li></ul></ul><ul><li>Atomic radius is measured in picometers </li></ul><ul><ul><li>1 x 10^-12 meters = 1 pm </li></ul></ul>
  4. 5. <ul><li>Ions </li></ul><ul><ul><li>An atom or bonded group of atoms that has a positive or negative charge </li></ul></ul><ul><ul><li>Occurs when an atom gains or loses an electron </li></ul></ul><ul><ul><li>Electrons are charged so you are gaining or losing a negative charge </li></ul></ul><ul><ul><ul><li>Affects the overall charge of the atom </li></ul></ul></ul><ul><li>Electrostatic repulsion </li></ul><ul><ul><li>Remember like charges repel each other…electrons in orbitals repel/push each other away </li></ul></ul>
  5. 7. <ul><li>Energy is needed to overcome the attraction between the positive protons and negative electrons </li></ul><ul><ul><li>Ionization energy (IE) is the energy required to remove an electron from a gaseous atom (kJ/mol) </li></ul></ul><ul><ul><li>IE indicates how strongly a nucleus can hold onto its valence e- </li></ul></ul><ul><ul><li>High IE= strong hold on e-; less likely to make positive ions </li></ul></ul><ul><ul><li>Low IE= atom can lose valence e- easily; likely to make positive ions </li></ul></ul>
  6. 8. More about ionization energy… <ul><li>After removing the 1 st e- it is still possible to remove additional electrons </li></ul><ul><li>Second ionization energy: </li></ul><ul><ul><li>The IE needed to remove a second electron from a +1 ion </li></ul></ul><ul><li>Third ionization energy: </li></ul><ul><ul><li>The IE needed to remove a third electron from a +2 ion </li></ul></ul>
  7. 9. Electronegativity <ul><li>Characteristic of an element that indicates the relative ability of its atoms to attract electrons in a chemical bond </li></ul><ul><li>Units: Paulings </li></ul><ul><li>Values are less than 3.98 or less </li></ul><ul><li>Leave out noble gases (they really don’t react) </li></ul>
  8. 10. Atomic Radius <ul><li>Electron cloud </li></ul><ul><ul><li>Spherical surface in which there is a 90% probability of finding an e- </li></ul></ul><ul><ul><li>Not physical </li></ul></ul><ul><li>Atomic size is defined by how closely an atom lies to its neighboring atom </li></ul><ul><ul><li>Each atom has different properties so there are going to be different sizes… </li></ul></ul><ul><ul><li>Different sizes in different blocks… </li></ul></ul>
  9. 12. Atomic Radius of a Metal <ul><li>Metals </li></ul><ul><ul><li>Atomic radius </li></ul></ul><ul><ul><ul><li>half the distance between adjacent nuclei in a crystal of that element </li></ul></ul></ul>
  10. 13. Atomic Radius of a Nonmetal <ul><li>Usually occur as molecules </li></ul><ul><li>Atomic radius: </li></ul><ul><ul><li>Half the distance between nuclei of identical atoms that are chemically bonded together </li></ul></ul><ul><ul><li>Diatomic molecules </li></ul></ul><ul><ul><ul><li>Hydrogen </li></ul></ul></ul><ul><ul><ul><li>Bromine </li></ul></ul></ul><ul><ul><ul><li>Iodine </li></ul></ul></ul><ul><ul><ul><li>Oxygen </li></ul></ul></ul>
  11. 14. Ionic Radius <ul><li>Losing/gaining electrons affects size of an atom </li></ul><ul><li>Gain an electron  atom becomes negative  atom becomes larger </li></ul><ul><ul><li>Electrostatic repulsion between atom’s outer electrons increase </li></ul></ul><ul><ul><ul><li>Forces outer electrons to move further apart </li></ul></ul></ul><ul><ul><ul><li>Makes radius bigger </li></ul></ul></ul><ul><li>Lose an electron  atom becomes positive  atom becomes smaller </li></ul><ul><ul><li>Electron lost is valence electron </li></ul></ul><ul><ul><ul><li>Can lead to completely empty orbital=smaller radius </li></ul></ul></ul><ul><ul><li>Electrostatic repulsion between atoms decrease so they can be pulled closer to nucleus </li></ul></ul>
  12. 15. Periodic Trend Scramble <ul><li>Break up into your first group </li></ul><ul><ul><li>Find everyone with the same type of card…all kings together, all queens together, etc…. </li></ul></ul><ul><li>Listen for instructions </li></ul>
  13. 16. Atomic Radius: Trends in Periods <ul><li>DECREASE in atomic radii left-to-right </li></ul><ul><li>Increasing positive charge in the nucleus </li></ul><ul><li>Principle energy level (n) remains the same throughout the period </li></ul><ul><ul><li>Each successive element the atomic # Increase </li></ul></ul><ul><ul><li>Add proton and electron </li></ul></ul><ul><ul><li>Electron gets added to same Prin. E level (n) </li></ul></ul><ul><ul><li>No additional electrons come across valence electrons and nucleus </li></ul></ul><ul><ul><ul><li>Val. E- are not shielded from increased nuclear charge </li></ul></ul></ul><ul><ul><ul><li>Therefore the increased nuclear charge brings the outermost electrons closer to the nucleus …which means… </li></ul></ul></ul><ul><ul><ul><li>Smaller atomic radii going    </li></ul></ul></ul>
  14. 17. Atomic Radius: Trends within Groups <ul><li>INCREASE as you move down a group </li></ul><ul><li>Nuclear charge increases </li></ul><ul><li>What happens to your principle energy level as you move down a group? </li></ul><ul><ul><li>Therefore…Electrons added to higher principle energy levels </li></ul></ul><ul><li>Although nuclear charge increased, other factors in play to overpower increased nuclear charge... </li></ul><ul><ul><li>Outermost orbital increases in size </li></ul></ul><ul><ul><ul><li>Electrons are farther from the nucleus b/c of bigger orbital </li></ul></ul></ul><ul><ul><ul><li>More resistant to higher nuclear charge b/c of increased distance </li></ul></ul></ul><ul><ul><li>Principle energy level increased </li></ul></ul><ul><ul><ul><li>Puts more orbital with electrons between the nucleus and the outermost electrons </li></ul></ul></ul><ul><ul><ul><li>These electrons in between shield the outermost electrons from the pull of the nucleus </li></ul></ul></ul>
  15. 19. Solve… <ul><li>Which has the largest radius? </li></ul><ul><ul><li>Magnesium (Mg) </li></ul></ul><ul><ul><li>Silicon (Si) </li></ul></ul><ul><ul><li>Sulfur (S) </li></ul></ul><ul><ul><li>Sodium (Na) </li></ul></ul><ul><li>Which has the smallest radius? </li></ul>
  16. 20. And the answer is… <ul><li>Largest: Na (sodium) </li></ul><ul><li>Smallest: S (sulfur) </li></ul>
  17. 21. Ionic Radius: Trends in Period <ul><li>What type of ions do you think will be formed on the left side of the table? </li></ul><ul><ul><li>Smaller positive ions </li></ul></ul><ul><li>What type of ions do you think will be formed on the right side of the table? </li></ul><ul><ul><li>Larger negative ions </li></ul></ul><ul><li>General Rule: </li></ul><ul><ul><li>Left-to-right across a period, the size of positive ions gradually decreases </li></ul></ul><ul><ul><li>Around 5A and 6A, the size of much larger negative ions gradually decreases </li></ul></ul>
  18. 23. Ionic Radius: Trends in Group <ul><li>What happens to the principle energy level as we move down a group? </li></ul><ul><ul><li>Increases </li></ul></ul><ul><li>Ion’s outer electrons are in a higher principle level </li></ul><ul><ul><li>This means an increase in ionic size </li></ul></ul><ul><li>Ionic radii increases as we move down a group for both positive and negative ions </li></ul>
  19. 25. Ionization Energy <ul><li>What type of IE does group 1A have? High or low? </li></ul><ul><ul><li>Low IE </li></ul></ul><ul><ul><li>Likely to form + ions </li></ul></ul><ul><li>What type of IE does group 8A have? </li></ul><ul><ul><li>High IE </li></ul></ul><ul><ul><li>Unlikely to form ions </li></ul></ul><ul><li>From left to right, the IE to remove successive electrons always increases </li></ul><ul><ul><li>Does not happen smoothly…requires large jump of energy </li></ul></ul>
  20. 26. IE continued…. <ul><li>Trends in periods: </li></ul><ul><ul><li>First IE generally increases as you move left-to-right </li></ul></ul><ul><ul><li>The nuclear charge increases with each successive element… </li></ul></ul><ul><ul><li>What does this have to do valence electrons? </li></ul></ul><ul><ul><ul><li>Increase the nuclear charge=stronger hold on valence electrons </li></ul></ul></ul>
  21. 27. IE continued… <ul><li>Trends within groups… </li></ul><ul><ul><li>First IE generally decrease as you move down a group </li></ul></ul><ul><ul><li>What happens to the size of an atom as you move down a group? </li></ul></ul><ul><ul><ul><li>Increases </li></ul></ul></ul><ul><ul><ul><li>This cause decrease in IE </li></ul></ul></ul><ul><ul><ul><li>Valence electrons are farther from the nucleus </li></ul></ul></ul><ul><ul><ul><li>Easier to remove </li></ul></ul></ul>
  22. 28. Octet Rule <ul><li>What is the electron configuration for sodium? </li></ul><ul><li>What is the new configuration when a sodium atom becomes a +1 sodium atom? </li></ul><ul><li>What noble gas does this configuration look like? </li></ul><ul><li>OCTET RULE: </li></ul><ul><ul><li>Atoms tend to gain, lose, or share electrons in an order to acquire a full set of valence electrons </li></ul></ul><ul><ul><li>First period elements are en exception to the rule </li></ul></ul><ul><ul><li>This rule helps to determine what kind of ions will form </li></ul></ul>
  23. 29. Food for thought…. <ul><li>Do atoms on the right side of the periodic table tend to gain or lose electrons? </li></ul><ul><ul><li>Gain electrons </li></ul></ul><ul><li>What type of ions are they likely to form? </li></ul><ul><ul><li>Negative ions </li></ul></ul><ul><li>Do atoms on the left side of the periodic table tend to gain or lose electrons? </li></ul><ul><ul><li>lose e- </li></ul></ul><ul><li>What type of ions do they form? </li></ul><ul><ul><li>Positive ions </li></ul></ul>
  24. 30. Electronegativity (EN) <ul><li>Fluorine is the most electronegative element </li></ul><ul><ul><li>Value: 3.98 </li></ul></ul><ul><li>Cesium and Francium are the least electronegative </li></ul><ul><ul><li>Values: 0.79 and 0.7 </li></ul></ul><ul><li>Atom with greater electronegativity attracts electrons in a chemical bond the strongest </li></ul>
  25. 32. Electronegativity (EN) <ul><li>Trends in periods and groups: </li></ul><ul><ul><li>EN decreases as you move down a group </li></ul></ul><ul><ul><li>Increases as you move left to right on table </li></ul></ul><ul><li>Where are the lowest electronegatives found? </li></ul><ul><ul><li>Lower left side of the periodic table </li></ul></ul><ul><li>Where are the highest electronegatives found? </li></ul><ul><ul><li>Upper right side of the periodic table </li></ul></ul>
  26. 34. Affinity What are some things you have an affinity for?
  27. 35. Electron Affinity <ul><li>The energy change that occurs when an electron is acquired by a neutral atom </li></ul><ul><li>Measure in kJ/mol </li></ul><ul><li>Many atoms release energy when they gain an electron </li></ul><ul><li>A + e-  A- + energy </li></ul><ul><li>A + e- + energy  A- </li></ul><ul><ul><li>Some atoms need energy to be “forced” to gain an electron </li></ul></ul><ul><ul><li>Produces unstable ions that lose electron quickly </li></ul></ul>
  28. 38. Study for Ch. 6 test!