Periodic Table and Periodic Trends



Matter & Periodic TableElemental OriginsOn the Periodic Table, not all of the elements are naturally occurringElements are created through a process that took place in stars before our solar system came into beingThis process is called stellar nucleosynthesisStars form when clouds of dust and hydrogen gas condenseAs this material condenses, pressure builds and temperatures reach millions of degreesThe energy that is produced help stars live for billions of yearsThe principle source of stellar energy is nuclear fusionFusion occurs when the nuclei of two or more atoms join together, to form the nucleus of a larger atomTypically – two H nuclei combine to produce one Helium nucleusThis is a type of nuclear reactionOther fusion reactions occur, depending on the mass of the star, the temperature of the star, & the stage of its developmentTwo He-4 atoms might combine to form Be-8; one He-4 & one Be-8 can fuse to form C-12When a star uses up all of the elements that fuel its fusion, the star is no longer stable, & it dies in a last great explosionThe elements that were formed within the star are flung into spaceWhen planets condense from this material, they take up the rich array of elements in the debrisElements heavier than Fe were created by supernovasOrganizing the ElementsA few elements, such as gold and copper, have been known for thousands of years - since ancient timesYet, only about 13 had been identified by the year 1700As more were discovered, chemists realized they needed a way to organize the elementsChemists used the properties of elements to sort them into groups.In 1829 J. W. D?bereiner arranged elements into triads – groups of three elements with similar propertiesOne element in each triad had properties intermediate of the other two elementsBy the mid-1800s, about 70 elements were known to existDmitri Mendeleev – a Russian chemist and teacherArranged elements in order of increasing atomic massThus, the first “Periodic Table” He left blanks for yet undiscovered elementsIn 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic numberThe arrangement used todayIntroduction to the Periodic TableElements are arranged in seven horizontal rows, in order of increasing atomic number from left to right and from top to bottomRows are called periods and are numbered from 1 to 7Elements with similar chemical properties form vertical columns, called groups, which are numbered 1 to 18Areas of the Periodic TableMetalsMalleable, lustrous, ductile, good conductors of heat and electricityNonmetalsGases or brittle solids at room temperature, poor conductors of heat and electricity (good insulators)MetalloidsDull, brittle, semi-conductors (high computer use)Show properties of both metals and nonmetalsElements can be sorted into four different groupings based on their electron configurations:Noble GasesRepresentative ElementsTransition MetalsInner Transition MetalsNoble gases are the elements in Group 18Previously called “inert gases” because they rarely take part in a reaction; very stable = don’t reactNoble gases have an electron configuration that has the outer s and p sublevels completely fullRepresentative Elements are in Groups 1-2 and 13-17Display wide range of properties, thus a good “representative” Some are metals, or nonmetals, or metalloids; some are solid, others are gases or liquidsTheir outer s and p electron configurations are NOT filledTransition metals are in the 3-12 columns of the periodic tableElectron configuration has the outer s sublevel full, and is now filling the “d” sublevelA “transition” between the metal area and the nonmetal area: examples are gold, copper, silverInner Transition Metals are located below the main body of the table, in two horizontal rowsElectron configuration has the outer s sublevel full, and is now filling the “f” sublevelFormerly called “rare-earth” elements, but this is not true because some are very abundantPeriodic Law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical propertiesHorizontal rows = periodsThere are 7 periodsVertical column = group (or family)Similar physical & chemical prop.Identified by number Periodic PropertiesAn element’s properties can go hand in hand with electron arrangementWe can use an element’s location on the PT to predict many propertiesAtomic radius (size of atoms)Ionization energyIonic Size (size of atoms)Electron affinityElectronegativityInfluenced by three factors:Energy LevelHigher energy levels are further away from the nucleusCharge on nucleus (# protons)More charge pulls electrons in closer (+ and – attract each other)Shielding effectBlocking effectShielding effectThe electron on the outermost energy level has to look through all the other energy levels to see the nucleusAtomic RadiiFirst problem: Where do you start measuring from?The electron cloud doesn’t have a definite edgeThey get around this by measuring more than one atom at a timeMeasuring the Atomic Radius - this is half the distance between the two nuclei of a diatomic moleculeAs we increase the atomic number (or go down a group). . .Each atom has another energy level, so the atoms get biggerGoing from left to right across a period, the size gets smallerElectrons are in the same energy levelBut, there is more nuclear chargeTherefore, outermost electrons are pulled closerIons – Ionization EnergySome compounds are composed of particles called “ions”An ion is an atom (or group of atoms) that has a positive or negative chargeAtoms are neutral because the number of protons equals electronsPositive and negative ions are formed when electrons are transferred (lost or gained) between atomsMetals tend to LOSE electrons, from their outer energy levelThus a positively charged particle is formed“cation”The charge is written as a number followed by a plus sign: Na1+Now named a “sodium ion”Nonmetals tend to GAIN one or more electronsChlorine will gain one electronCl1- is re-named a “chloride ion”Negative ions are called “anions”Trends in Ionization EnergyIonization energy is the amount of energy required to completely remove an electron (from a gaseous atom)Removing one electron makes a +1 ionThe energy required to remove only the first electron is called the first ionization energyThe second ionization energy is the energy required to remove the second electronAlways greater than first IEThe third IE is the energy required to remove a third electronGreater than 1st or 2nd IEThe greater the nuclear charge, the greater IEGreater distance from nucleus decreases IEFilled and half-filled orbitals have lower energy, so achieving them is easier, lower IEShielding effectDriving Force for IEFull Energy Levels require lots of energy to remove their electronsNoble Gases have full orbitalsAtoms behave in ways to try and achieve a noble gas configurationGroup Trends for IEAs you go down a group, the first IE decreases because...The electron is further away from the attraction of the nucleus, and there is more shieldingPeriod Trends for IEAll the atoms in the same period have the same energy levelSame shielding, but increasing nuclear chargeSo IE generally increases from left to right with an exception for full and ? full orbitalsTrends in Ion SizeCations: form by losing electronsSmaller than the atom they came from – not only do they lose electrons, they lose an entire energy levelMetals form cationsAnions form by gaining electronsAnions are bigger than the atom they came from – have the same energy level, but a greater area the nuclear charge needs to coverNonmetals form anionsTherefore, ions always have noble gas configurations ( = a full outer level)Electron AffinityAnother periodic trend dealing with an e- is electron affinity which is a measure of the ability of an atom to attract or gain an electronAtoms that tend to accept an e- are those that tend to give a neg. chargeThe closer to a full outer shell an atom has, the higher the affinity (more neg. the measurement)Trends in ElectronegativityElectronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another elementThey share the electron, but how equally do they share it?An element with a big electronegativity means it pulls the electron towards itself strongly! The further down a group, the farther the electron is away from the nucleus Plus the more electrons an atom hasThus, more willing to shareLow electronegativityMetals are at the left of the tableThey let their electrons go easily, thus, low electronegativityAt the right end are the nonmetalsThey want more electrons and try to take them away from othersHigh electronegativity ................
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