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Periodic Trends

Periodic Trends. Review. Where are protons located? nucleus Where are e- located? orbitals Which has greater mass? protons. Basic Idea Behind Trends. As you move across a period (left to right) OR down a group/family, characteristics of elements change consistently. Atomic Number Trend.

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Periodic Trends

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  1. Periodic Trends

  2. Review • Where are protons located? • nucleus • Where are e- located? • orbitals • Which has greater mass? • protons

  3. Basic Idea Behind Trends • As you move across a period (left to right) OR down a group/family, characteristics of elements change consistently

  4. Atomic Number Trend • As you move across a period (Left to right) • Atomic number increases • As you move down a group/family • Atomic number increases

  5. Average Atomic Mass Trend • As you move across a period (Left to right) • Average atomic mass increases • As you move down a group/family • Average atomic mass increases • Find the exceptions: • Te & I • Co & Ni • U & Np

  6. Trends • In trends we are more concerned with general instances than with specific details.

  7. Review on e- • All elements want to be like • Noble gases • This means they want • Stability [full valence e-: outer shell e- (s & p)] • Octet rule : 8 valence e- • Electrons are mobile. For which elements does it make more sense to lose electrons than to gain electrons? • Families starting with H, Be, B – metals want to lose • Which elements are more likely to gain electrons? Why? • Families starting with N, O, F, - non metals want to gain

  8. Review e- Cont’d • Metals tend to be scatterbrained (cations) meaning they will most likely lose electrons, giving them a positive charge. • Nonmetals tend to be thieves (anions) meaning they will most likely gainelectrons, giving them a negativecharge.

  9. In the following, tell me how many electrons the element should gain or lose to have the same electron configuration as a noble gas, then list the noble gas, and the charge on the element.

  10. All elements want Stability. • Statements on Stability: • 1. elements with completely full sublevels are very stable • 2. elements with completely filled “p” sublevels (full valence shells) are most stable (Noble gases) • 3. elements with exactly half-filled sublevels are reasonably stable. * This means that elements, while preferring completely filled sublevels, will also work to make exactly half filled sublevels.

  11. How many electrons will exactly half fill the following sublevels: • s • p • d • f • We will now focus on transition elements a little bit more: • Side note: As of now, I will use the terms “charge” and “oxidation state” or “oxidation number” interchangeably.

  12. Based on what we have learned, why might transition elements have multiple charges?

  13. Atomic Radii Info • What is atomic Radii? • Half the distance between the nuclei of identically bonded atoms. (size of atom) • Diatomic elements: • H2O2N2Cl2Br2I2F2

  14. Brainstorming Atomic Radii trend • What happens to the number of protons as you move down the periodic table? • increases • What happens to the energy levels of the outermost electrons? • increases • What do you think happens to the radius of an element as you move down the periodic table? Why? • Increases b/c of the nrg levels of the e-

  15. Brainstorming Atomic Radii Trend cont’d • What happens to the number of protons as you move across the periodic table (from left to right)? • increases • What happens to the energy levels of the outermost electrons? • Stay the same • What do you think happens to the radius of an element as you move across a period from left to right? Why? • Decreases, e- moved closer to the nucleus (rubber band demo)

  16. You will find the same causes at the root of all trends. • Cause #1 • # of protons (atomic number) • Cause #2 • Nrg level (due to e- shielding) • E- shielding: e- are pulled to the nucleus but the inner shell e- push out the outer shell e- (little kids soccer example) • (Cause #3) • Based on 1 & 2, atomic size

  17. Therefore, ATOMIC RADII TREND • As you move across a period from left to right, atomic radii • decreases • As you move down a group, atomic radii • increases

  18. Energy is currency!

  19. Ionization energy trend • Ionization Energy: • The amount of energy you have to “pay” to remove an e- • Video: http://www.youtube.com/watch?v=m55kgyApYrY • In metals, as a generalrule • The lower the ionization energy (IE), the more reactive the metal • As you move down a group, ionization energy • decreases

  20. Now let’s think about moving across a period and IE: First let’s review the three causes of all trends: • What happens to # of protons as you move across a period? • increases • What happens to e- shielding as you move across a period? • Stays the same • What happens to atomic size, as you move across a period? • Decreases (gets smaller)

  21. IEacross a period cont’d • In other words you have moreprotons in the nucleus, the same e- shielding & smaller atoms. • Will it be easier or harder to take away electrons? • harder • As you move across a period, ionization energy • increases

  22. Therefore, Ionization Energy • As you move across a period, ionization energy • increases • As you move down a group, ionization energy • decreases

  23. Electron Affinity • Electron Affinity: • The amount of nrg an atom will “pay” to get an e- • How are electron affinity and ionization energies similar? • Deal with movement of e- • Same trend • How are they different? • IE is to get rid of an e- • EA is to gain an e-

  24. Electron Affinity Trend • Proceeding left to right across a period, electron affinity • increases • Proceeding down a group, electron affinity • decreases • NOTABLE EXCEPTION: • Noble Gases

  25. Electronegativity • Electronegativity: • The attraction an atom has for the e- in a bond • (the tug-o-war in covalent bonding b/c sharing e-) • Which element wants electrons the most? • Fluorine • Which element wants electrons the least? (other than noble gases) • Francium

  26. Electronegativity Trend • Moving across a period from left to right, electronegativity • increases • Moving down a group, electronegativity • decreases

  27. At this point you know the trends. But the more important question (*test questions*) would be why the trends happen. • Atomic radii: size of the atom • Trend is: • Across -> atomic radii decreases Why? Add protons = smaller atoms • Down -> atomic radii increases Why? Add nrg levels = bigger atoms • Ionization energy: nrg to get rid of e- • Trend is: • Across -> IE increases Why? Add more p+= more compact= harder to remove • Down -> IE decreases Why? More reactive = lower IE

  28. At this point you know the trends. But the more important question (*test questions*) would be why the trends happen. (cont’d) • Electron Affinity: amount nrg to gain e- • Trend is: • Across -> EA increases • Down -> EA decreases Why? Bartering: If you want to be a noble gas= you pay • Electronegativity: attraction an atom has for e- in a bond • Trend is: • Across -> IE increases • Down -> IE decreases Why? Closer to the Noble gas = more pull you have to make a bond

  29. Given the following elements, tell me which has the largest atomic radii, highest ionization energy, highest electron affinity, and the highest electronegativity.

  30. Ionic Radius Trend • Ionic Radius (size of Ions) • Cations (positive ions) are smaller than the noble gas they are like. • Why? • lose e- = less nrg levels (e-shielding) • lose e- = more protons  = e- pulled closer to nucleus • Anions (negative ions) are larger than the noble gas they are like. • Why? • More e- = higher nrg levels = further from the nucleus

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