periodic table

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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

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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

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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 History of the Periodic Table

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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

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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

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As we examine atomic radius from left to right across the PT we see a grad-ual 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

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The change in atomic radii across the PT is due to e- shielding or to nuclear effect 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

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We are also adding protons into the nucleus which increases the p+-e- interaction (attraction) So the nucleus gains strength while the e- are’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

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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

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

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Elements in a group tend to form ions of the same charge. Modeled by electron configurations. Periodic Properties

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[He] [He] O: Periodic Properties

Periodic Trend of Ionic Charges : 

Periodic Trend of Ionic Charges

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

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

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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

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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. Periodic Properties

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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-

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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

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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

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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

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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 Periodic Properties

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