PERIODICITY

1. PERIODICITY

2. History of the Periodic Table • 70 elements had been discovered by the mid-1800’s, but until Dmitri Mendeleev, no one had a come with a way to organize the elements. • Mendeleev came up with the first working system of filing the elements. • He listed the elements in columns in order of increasing atomic mass, and then put columns together that were similar

4. History of the Periodic Table • Mendeleev left gaps in the table since there were no current elements that seemed to fit those spots • Those elements were eventually discovered and they fit perfectly into an open spot. • The 1st scientist that set the table in order of atomic number was Henry Moseley

6. History of the Periodic Table • The modern PT is arranged by increasing atomic number • Increases from left to right, and top to bottom • This establishes the periodic law • When the elements are arranged in order of increasing atomic #, there is a periodic repetition of their phys & chem properties

7. PNICOGENS CHALCOGENS

9. Periodic Properties • An element’s properties can go hand in hand with electron arrangement • We can use an element’s location on the PT to predict many properties. • Atomic radius • Electron affinity • Electronegativity • Ionization energy • Ionic Size

10. 99 pm 198 pm Periodic Properties • The radius of an atom is defined by the edge of its last energy level. • However, this boundary is fuzzy • An atom’s radius is the measured distance between the nuclei of 2 identical atoms chemically bonded together - divided by 2.

11. Periodic Properties • As we examine atomic radius from left to right across the PT we see a grad-ualdecrease in atomic size. • As e- are added to the s and p sublevels in the same energy level, they are gradually pulled closer to the highly positive nucleus • The more e-’s in the atom the less dramatic this trend looks

13. Periodic Properties • The change in atomic radii across the PT is due to e-shielding or to the effective nuclear charge • As we move across the PT we are adding e- into the same gen- eral vol. in which case they will shield or interact with each other (repulsion)

14. Periodic Properties • We are also adding protons into the nucleus which increases the p+-e- interaction (attraction) • So the nucleus gains strength while the e- aren’t gaining much distance, so the atom is drawn in closer and closer to the nucleus. • Decreasing the overall radius of the atom

17. Periodic Properties • How does the size of an atom change when electrons are added or removed? As an Atom loses 1 or more electrons (becomes positive), it loses a layer therefore, its radius decreases.

18. Periodic Properties • How does the size of an atom change when electrons are added or removed? As an Atom gains 1 or more electrons (negative), it fills its valence layer, therefore, its radius increases.

20. Loses 1 electron 4s 4s [Ar] K: [Ar] +1 K Wants a full set of e- Periodic Properties • Elements in a group tend to form ions of the same charge. • Modeled by electron configurations.

21. Gains 2 electrons 2s2 2p4 Wants a complete set -2 O Periodic Properties O: [He] [He]

22. 18 1 2 13 14 15 16 17 3 4 5 6 7 8 9 10 11 12 +1 tend to have +2 -2 -1 +3 -3 +/- 4 more than one option + 3 + 3 or + 4 Periodic Trend of Ionic Charges

23. The Transition Elements are almost unpredictable, and sometimes have more than one possible charge -- due to d orbitals --

24. Tend to lose electrons to become positive Tend to gain electrons to become negative

25. Periodic Properties • Another periodic trend on the table is ionization energy (a.k.a. potential) • Which is the energy needed to remove one of an atoms e-s. • Or a measure of how strongly an atom holds onto its outermost e-s. • If the e-s are held strongly the atom will have a high ionization energy

28. Periodic Properties • The ionization energy is generally measured for one electron at a time • You can also measure the amount of energy needed to reach in and pluck out additional electrons from atoms. • There is generally a large jump in energy necessary to remove additional electrons from the atom.

29. the amount of energy required to remove a 2p e– (an e- in a full sublevel) from a Na ion is almost 10 times greater than that required to remove the sole 3s e-

30. Periodic Properties • There is simply not enough energy available or released to produce an Na2+ ion to make the compndNaCl2 • Similarly Mg3+ and Al4+ require too much energy to occur naturally. • Chemical formulas should always describe compounds that can exist naturally the most efficient way possible

31. Periodic Properties • Another periodic trend dealing with an e- is electron affinity • Which is a measure of the ability of an atom to attract or gain an electron. • Atoms that tend to accept an e- are those that tend to give a neg. charge. • The closer to a full outer shell an atom has, the higher the affinity (more neg. the measurement)

34. Periodic Properties • An atoms ability to lose an e- or gain an e- can be used to understand the Octet Rule • Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons. • 2 e- in the outermost s sublevel + 6 e– in the outermost p sublevel= a full valence shell

36. LEAST STABILITY NO SPECIAL ARRANGEMENT HALF-FULL SUBLEVEL FULL SUBLEVEL FULL VALENCE LEVEL -OUTER LEVEL GREATEST STABILITY

37. Periodic Properties • Electronegativity is a key trend. • It reflects the ability of an atom to attract electrons in a chemical bond. • Fis the most electronegative element and it decreases moving away from F. • Electronegativity correlates to an atom’s ionization energy and electron affinity

40. INCREASES INCREASES BOILING POINT & MELTING POINT VS. ATOMIC NUMBER

43. Elemental Origins • On the PT, only the elements through 92 are naturally occurring • Elements are created through a process that took place in stars before our solar system came into being • This process is called stellarnucleosynthesis.

44. Elemental Origins • Stars form when clouds of dust and hydrogen gas condense • As this material condenses, pressure builds and temperatures reach millions of degrees • The energy that is produced help stars live for billions of years • The principle source of stellar energy is nuclear fusion

45. Elemental Origins • Fusion occurs when the nuclei of 2 or more atoms join together, to form the nucleus of a larger atom • Typically – 2 H nuclei combine to produce one He nucleus.

46. Elemental Origins • This is a type of nuclear rxn • The mass of helium nucleus formed in the fusion process is slightly less than the mass of the four hydrogen nuclei that went into it. • This small amount of “missing” mass is converted to energy according to Einstein’s eqn E=mc2

48. Elemental Origins • The mass of combining nuclei supplies the enormous energy that stars use to shine • Nuclear fusion is not only the princ-iple source of energy for stars, but also the process by which elements heavier than H are created. • The sun converts about 400 million tons of H into He every second

49. Elemental Origins • Other fusion rxns occur, depending on the mass of the star, the temp. of the star, & the stage of its developmnt • 2 He-4 atoms might combine to formBe-8; 1 He-4 & 1 Be-8 can fuse to formC-12 • When a star uses up all of the ele-ments that fuel its fusion, the star is no longer stable, & it dies in a last great explosion

50. Elemental Origins • The elements that were formed within the star are flung into space • When planets condense from this material, they take up the rich array of elements in the debris. • Elements heavier than Fe were created by supernovas