The Periodic Table Chapter 6

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Steps to the Periodic Table Chemists used the properties of elements to sort them into groups. Triads (Dobereiner) – 3 elements that were similar in properties and the lightest and heaviest averaged to the middle Ex) Cl = Iodine = /2 equals Bromine 79.9 Periodic Table (Meyer and Mendeleev) – Sorted the elements based on atomic mass – The similar elements are organized into groups, which “flow” through periods

Periodic Law When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern – Must be sorted based on atomic number, not mass

3 Classes of Elements MetalsNon-MetalsMetalloids % of elements~80%~15%~6% LusterShiny/brightNo/little lusterMedium Bend or break? Malleable and ductile (bendable) Not malleable or ductile (brittle) Brittle State at room temperature (usually) SolidGasSolid DensityHIGHLowMedium Conductivity (electricity and heat) High Conductivity Low Conductivity (Insulator) Semi-conductors (Can be manipulated depending on conditions)

There is more than it seems… The periodic table can tell you: – Element Symbol and Name – Classes of elements Metal, non-metal, metalloid – Groups of elements Electron configurations – Energy levels Electrons in each – Atomic mass and number – State of matter (g, l, s) – And so much more!

Groups and Periods Groups (or families) form columns (vertical) – Have similar physical and chemical properties (reactivity, melting point, color, etc) Periods form ROWS – The repetition of the groups with larger and larger sizes. – Also shows the energy levels described by Bohr, Heisenberg and Schrödinger

Groups of Elements The columns in the periodic table are called “Groups” or “Families” – Elements in the same group have very similar physical and chemical properties (like family members) There are 18 groups (ignoring the f-orbital metals, for some reason) 4 groups are important and very different from the other 14: – Alkali Metals – Group 1 – Alkaline Earth Metals – Group 2 – Halogens – Group 7 – Noble Gasses – Group 8

WHY?!? Elements in the same group have the same electron configurations! – Electron configuration determines how an atom reacts with other atoms. – Group 1 (Alkali metals) are s1 – Group 2 (Alkaline earth metals) are s2 – Group 7 (Halogens) are s2p5 – Group 8 (Noble gasses) are s2p6

Periodic Trends The elements in the Periodic Table can be used to predict properties like: – Atomic Size – What Ions are formed. – Ionization energy – Ionic size – Electronegativity

Atomic Size Two things determine how large an atom is: – Number of protons More protons = smaller – Number of energy levels More energy levels = larger The energy levels below “shield” the electrons from the nucleus Atoms are larger in higher periods and smaller with higher groups – Ex) Francium is very large, Fluorine is very small.

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Ions and Ionic Charge Atoms become ions when they lose or gain electrons – Changes the charge from neutral to positive (when electrons are lost) or negative (when electrons are gained) Cations (+) – I like cats, so cations are positive Anions (-) – I don’t like onions, so they are negative Cations are on the left, anions are on the right. – Cations are metals, anions are non.

The goal of all atoms. Get full or empty energy levels. – Either fill up s and p, or empty them completely. Elements in the d orbital just want to get rid of them.

Ionization Energy How much energy it takes to take away an electron – Higher as you get closer to the noble gasses’ configuration. Full (or empty) s and p orbitals – First ionization energy is higher at the top and the right side of the table Ex) F is high, Fr is low

Ionic Size Cations (+) are smaller than their original atoms Anions (-) are larger – Ex) C 4+ is smaller than C 4- The same rules from atomic size (more energy levels = larger)

Electronegativity How much an atom is attracted to electrons – How much it “wants” an electron, or wants to give it away – Tells us how atoms treat their electrons Electronegativity is highest at top right – Lowest at bottom left

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WHY?!?!? The atomic structure (protons, electrons, and energy levels) determine the periodic trends that exist.