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PERIODICITY Electron Configurations • Don’t have to write out the entire electron configuration. • There is a short-cut: – Keeps focus on valence electrons – An atom’s inner electrons are represented by the symbol for the nearest noble gas with a lower atomic number. K: [Ar]4s1 Electron Configurations For the element Phosphorus -- 15 electrons 1s22s22p63s23p3 P: [Ne] Must be a Noble gas (One just before Element) Electron Configurations Let’s do a couple more: Ba: [Xe] 2 6s Hg: [Xe] 6s2 4f14 5d10 V: [Ar] 4s2 3d3 Exceptions to the order of filling Electron Configurations • The chemistry of an atom occurs at the set of electrons called valence electrons • The valence electrons are electrons in an atom’s highest energy level. – For the Group – A elements, it is the outermost s & p e- of the atom. – Specifically the 2 s electrons + 6 p electrons (octet electrons) • The arrangement of the valence elead to the element’s properties. 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 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 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 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 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. Periodic Properties • As we examine atomic radius from left to right across the PT we see a gradual decrease 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 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 general vol. in which case they will shield or interact with each other (repulsion) Periodic Properties – We are also adding protons into the nucleus which increases the p+-einteraction (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 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. 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. Periodic Properties • Elements in a group tend to form ions of the same charge. – Modeled by electron configurations. K: [Ar] 4s Loses 1 electron [Ar] Wants a full set of e- 4s Periodic Properties O: [He] 2s2 Wants a complete set 2p4 Gains 2 electrons [He] Periodic Trend of Ionic Charges The Transition Elements are almost unpredictable, and sometimes have more than one possible charge -- due to d orbitals -- Tend to lose electrons to become positive Tend to gain electrons to become negative 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 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. 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- Periodic Properties • There is simply not enough energy available or released to produce an Na2+ ion to make the compnd NaCl2 – 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 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) 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 Periodic Properties • Electronegativity is a key trend. – It reflects the ability of an atom to attract electrons in a chemical bond. – F is the most electronegative element and it decreases moving away from F. • Electronegativity correlates to an atom’s ionization energy and electron affinity BOILING POINT & MELTING POINT VS. ATOMIC NUMBER INCREASES INCREASES 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 stellar nucleosynthesis. 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 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. 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 Elemental Origins • The mass of combining nuclei supplies the enormous energy that stars use to shine – Nuclear fusion is not only the principle 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 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 form Be-8; 1 He-4 & 1 Be-8 can fuse to form C-12 • When a star uses up all of the elements that fuel its fusion, the star is no longer stable, & it dies in a last great explosion 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 Elemental Origins • On earth, which is considered a closed system, most elements are found in biogeochemical cycles. – Elements are recycled through processes that keeps the amount of elements on earth constant. – The “big six” cycles important for life are carbon, water, oxygen, phosphorus, nitrogen, sulfur Homemade Elements • The first artificial isotope was created in 1919 – particles were being used to produce elements in the lab • Scientists were taking particles and colliding them with nitrogen atoms • This led to the fusion of nuclei to form a synthetic isotope of oxygen Homemade Elements • This was the first incident in which one element was transformed into another in a lab. • Today, scientists change one element into another by bombarding nuclei with various small particles – Protons, neutrons, alpha particles, and beta particles (fast moving electrons) Homemade Elements • These “nuclear bullets” react with the nuclei they are aimed at forming isotopes of naturally occurring elements • Numerous synthetic elements are created with this method – All of the elements with atomic #s greater than 92 but less than 101 were created with this process Homemade Elements • The particles must be moving at extremely fast speeds and with a huge amount of energy in order to actually fuse rather than simply bouncing off of one another – A device called a “Particle Accelerator” is used to accomplish this task Homemade Elements • Elements with atomic # 101 & greater have been created by a colliding whole atoms rather than particles. – To make the bigger atoms, special accelerators hurl entire atoms at one another • Nobelium was created by crashing together Ca and Pb Homemade Elements • The discovery of element 109 has been thoroughly verified and accepted – It is extremely unstable – Only 3 atoms of element 109 have ever been produced – They only existed for a short time (.0034 seconds) Homemade Elements • Scientists are hoping to discover other heavier atoms that might be more stable, because of the nature of their nuclei • The “atom smashers” they plan to use are technological marvels, and there are only a few in the world Homemade Elements • An accelerator is a linear or circular device that is used to increase the velocity of charged particles • When the particle has been given a very high velocity and thus a very high energy, it is aimed at a target material. Homemade Elements • The collision can help scientists discover new info. About the nucleus, & sometimes create a heavier atom. Homemade Elements • A typical accelerator is circular in shape • Particles are accelerated by electric fields in several locations around the ring. • The particle’s path is confined to the ring by huge magnets. Homemade Elements • The greater the energy of the collision between the accelerated particles with the target. • The more scientists can learn about the structure and the behavior of the nucleus