Periodic Law

Periodic LawDo Now: What does an elements position on the periodic table indicate about its properties?

Organizing the ElementsCu, Ag, Au are three of the oldest known elements.By the year 1700, only 13 elements had been identified and isolated.From 1765-1775, five new elements including H, N, and O had been isolated.As soon as elements were (are) identified, scientists begin to look for similarities and classify them.3Classifying ElementsJW Dobereiner published a classification system in 1829.Elements grouped in triads (3 elements with similar properties)Couldnt group all elements using that systemDmitri Mendeleev published a table of elements in 1869Organized in order of increasing atomic mass4periodic tablesMendeleevs Table

When classifying elements, Mendeleev organized according to atomic mass. He left spaces (look for question marks) where undiscovered elements would most likely fit. As these elements were discovered, their properties nearly matched those he predicted. His table gained widespread acceptance.6Pledge Comic The Periodic LawIn developing the Periodic Table, Mendeleev noticed problems. Atomic mass order didnt always match periodic trends.The table was eventually rearranged according to atomic number. In the modern periodic table, elements are arranged in order of increasing atomic number.8Rows or Periods7 rows (called periods) on the periodic tablePeriod 1 has 2 elementsPeriod 2 has 8 elementsPeriod 4 has 18 elementsPeriod 6 has 32 elementsEach period corresponds to a principle energy levelHigher periods have more elements because there are more orbitals in higher energy levels9Columns or GroupsGroups have similar properties.Properties change across a period but those properties repeat as you move from period to periodPeriodic Law: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.10The properties of an element are similar to those of other elements in the same group.Periodic Law:When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Horizontal rows = periods There are 7 periods Vertical column = group(or family) Similar physical & chemical prop. Identified by number & letter (IA, IIA)Metals, Nonmetals, Metalloids3 broad classes of elementsAcross a period, elements become less metallic, and more nonmetallic

Metals, Nonmetals, and Metalloids

15Basic Properties of Elements16Metals80% of the elements are considered to be metallicFreshly cut metals have high luster

All metals are solid at room temperature-except HgMost metals are ductile and malleable (can be drawn into wires and hammered into thin sheets)

NonmetalsMOST nonmetals are gases at room temperatureSome are solids (carbon, sulfur, etc)One is a liquid- bromine Poor conductors of electricity Exception-carbonhttp://www.boston.com/bigpicture/2009/06/sulfur_mining_in_kawah_ijen.html

Volcanic eruptions deposit yellow sulfur deposits and make the lake acidic Kawah Ijen Eastern Java Indonesia 20Metalloidsstair step line separates metals from nonmetals-the elements along this line are known as metalloidsHave properties similar to metals and nonmetalsChemists do not always agree on which elements to classify as metalloidshttp://www.ehow.com/info_8675759_uses-metalloids-industry.htmlDo NowWhich of the following is least likely to be a metalloid?A. AsB. HgC. GeD. SiE. Sb

Classifying ElementsSquares in the Periodic Table tell us:Atomic #Element name-black/solid, gases/red, blue/liquidAverage atomic massVertical column of numbers in the top right corner-number of electrons in each occupied energy level

BDo NowChemical properties of the elements are defined by theA. ElectronsB. Ionization energyC. ProtonsD. NeutronsE. electronegativityASort Elements based on Electron Configuration Noble gases- s and p sublevels full ex: Ar 1s22s22p63s23p6 Representative elements- Group 1A-7A group #=# of electrons in highest occupied energy levelTransition MetalsTransition metals-have electrons in the d orbitalsInner transition metals- have electrons in the f orbital

In a chemical reaction, the outermost electrons make first contact this is why elements with similar electron structures have similar chemical propertiesEx: all of the elements in group VII have s2p5 in the outermost shell, so they are all going to want to gain an electron to make a stable octet QuestionsWhat 4 classes can elements be sorted based on their electron configuration?

Representative elements, noble gases, transition metals, inner transition metalsHow many electrons are in the highest energy level of a Group 5A element?5Locate the block this element can be found based on its electron configuration:1s22s22p63s23p64s23d61s22s22p63s23p63d64s2Transition metalClassifying the elements even further..

Family (Group) Names Group I - Alkalai metalsGroup II Earth metalsGroup III Boron groupGroup IV Carbon groupGroup V Nitrogen groupGroup VI Oxygen group (Chalcogens)Group VII Halogens Group VIII Noble Gases

Do NowA solid element has 2 valence electrons. That element must be A. A halogenB. A noble gasC. A radioactive element D. an alkalai metalE. An alkaline earth metalDo NowWhich pair of elements is expected to have the most similar properties?A. Potassium and lithiumB. Sulfur and phosphorusC. Silicon and carbonD. Strontium and bariumE. Fluorine and iodine Atomic SizeThe electron cloud does not have an edge, it is a probabilityso how can we measure how large these atoms are?Measure more than one at a timeAtomic radius- how we measure the size of an atom- defined as half the distance between 2 nuclei of a diatomic molecule

Total Distance between 2 nuclei

NucleusAtomic radiusALL periodic trends Are influenced by 3 factors:1. Energy Level- higher energy levels are farther away from the nucleus2. Charge on nucleus (number of protons)- the more charge pulls electrons closer (+ and attract)

3. Shielding- electrons in lower energy levels block the positive pull of the nucleus from the outer electrons

Periodic Trends 1. ATOMIC RADIUSGoing from left to right across a period the atomic radius (size) gets smaller because:Electrons are in the same energy levelBut there is more nuclear chargeOutermost electrons are pulled closerNa Mg Al Si PATOMIC RADIUS cont.Within a GROUP, the atomic radius gets larger because:ShieldingEnergy levels

Atomic Radii

2. IONIZATION ENERGY Ion- an atom or a group of atoms that has a positive or negative chargeFormed when electrons are transferredMetals tend to lose electronsthat has a positive or negative charge

Ex: Sodium loses one: there are now more protons (11) than electrons (10), and thus a positively charged particle is formed Positive ions = cation The charge is written as a number followed by a plus sign: Na1+ Now named a sodium ionNonmetals tend to gain one or more electrons- known as anionsEx: Chlorine will gain one electron- protons (17) no longer outnumber the electrons (18) So now has a charge of Cl-1 Known as a chloride ionIonization energy- the amount of energy needed to completely remove an electronThe energy required to remove the first electron is called the First Ionization Energy1st 2nd 3rd H 1312 He 2731 5247 Li 520 7297 11810 Be 900 1757 14840 B 800 2430 3569 C 1086 2352 4619 N 1402 2857 4577 O 1314 3391 5301 F 1681 3375 6045Ne 2080 3963 6276Factors that influence ionization energy (IE)The greater the nuclear charge, the greater the IEThe greater the distance from the nucleus, decreases the IEShielding

Mg (g) + 738 kJ ---> Mg+ (g) + e-This is called the FIRST ionization energy because we removed only the OUTERMOST electronMg+ (g) + 1451 kJ ---> Mg2+ (g) + e-This is the SECOND IE.

IE = energy required to remove an electron from an atom (in the gas phase).Ionization Energy

As you go down a group, the first IE decreases becauseThe electron is farther away from the attraction of the nucleusThere is more shieldingFrom left to right across a period, IE generally increasesAll atoms have the same amount of shielding but increase nuclear chargeWhich has a higher 1st ionization energy?Mg or Ca ?Al or S ?Cs or Ba ?

Do Now: Ionization EnergyWhich representative element has the largest first ionization energy? Explain your answer.

3. IONIC SIZECations are smaller than the atoms they came from lost an entire energy level

Anions are larger than the atom it started from

Ion SizesANIONS are LARGER than the atoms from which they come.The electron/proton attraction has gone DOWN and so size INCREASES.Trends in ion sizes are the same as atom sizes. Forming an anion.F, 71 pm9e and 9pF-, 133 pm10 e and 9 p-Within a group, ions get larger as you go down as a result of adding an energy level

Across a period from left to right the nuclear charge increases so the ionic size gets smallerUNTIL you reach the anionsTrends in Ion Sizes

Figure 8.13Which is Bigger?Cl or Cl- ?K+ or K ?Ca or Ca+2 ?I- or Br- ?

4. ELECTRONEGATIVITYElectronegativity-the tendency for an atom to attract electrons to itself when it is chemically combined to another elementAn atom with a large electronegativity means it pulls electrons towards itselfElectronegativity, is a measure of the ability of an atom in a molecule to attract electrons to itself.

Concept proposed byLinus Pauling1901-1994

Electronegativity

Which is more electronegative?F or Cl ?Na or K ?Sn or I ?

`Within a group the farther down the group, the farther away the electron is from the nucleus, low electronegativity

Within a period metals are on the left, they let their electrons go easily- low electronegativity

Nonmetals on the right, they want more electrons high electronegativity75Summary of Electronegativity trendElectronegativity increases from left to right across a period Electronegativity decreases from top to bottom within a group5. DENSITYincreases from top to bottom within a group due to smaller change in atomic size and a large change in atomic mass6. Melting points and boiling points of metalsdecrease from top to bottom within a group due to atomic size6. Melting Points and Boiling points of nonmetalsincrease from top to bottom within a groupDue to atomic size/nuclear charge Do NowThe best way to estimate the boiling point of Pd is to A. Average the bp of Rh and AgB. Average the bp of Ni and PtC. Average the bp of Ir and CuD. Average the bp of Co and AuE. None of these will work 7. Metallic character Increases from top to bottom within a groupDecreases from left to right across a period 8. Electron AffinityThe energy change that occurs when an electron is added to a gaseous atom to form a negative ionA measure of how much an element wants to accept another electronIf the value is negative it releases energyIt wants to accept the electronThe more negative, the more it wants to acceptIf the value is positive, it requires energyIt does not want to accept the electron

PeriodicityThe predictable physical and chemical trends that occur as one moves across a period or down a group in the periodic tableSummary of Trends

The End !!!!!!!!!!!!!!!!!!!