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11.14.11
• Test postponed – – review tonight: pp 126 #’s 43, 48, 50, 51 – HW for Wednesday (due Wednesday, that is) – Read secHon 5.1, answer quesHons 1-‐4 on p 137
• Warmup: how do you find out the number of valence electrons for an element?
• MSFWBAT – Explain the periodicity in the periodic table for ionizaHon energy, electron affinity, electronegaHvity, atomic radii
– Define the terms in the previous objecHve
The periodic table
• Early a\empts to organize elements based on weight, various properHes, but scienHsts believed a fundamental pa\ern must exist
• A fundamental discovery (which we’ll get to later in the year) revealed that for all substances in gas phase occupied the same volume
• Based on this, a systemaHc way for idenHfying elements by weight was developed
• Dmitri Mendeleev was the first to organize the elements according to their atomic mass & their properHes.
• He observed that when elements were arranged by increasing atomic mass, similariHes in properHes occurred at regular intervals…called periodic.
• The periodic table was born.
Henry Moseley later modified Mendeleev’s table by organizing the elements by atomic number rather than atomic mass.
Periodic Law
• The physical and chemical properHes of the elements appear at regular intervals (periodic) when arranged by atomic number.
• The rows on the periodic table are called periods.
• How many periods are there?
• The columns on the periodic table are called families or groups.
• How many families are there?
• h\p://library.thinkquest.org/06aug/00318/Images/periodic_table.gif
11.16.11
• Warmup: what does periodic mean? • HW tonight: p149 quesHons 1-‐5
• ObjecHves: explain the periodic trends relaHng to valence, atomic radii, ionic radii, electron affinity, electronegaHvity, ionizaHon energy
Atomic radii
• Measured as half the distance between the nuclei of idenHcal atoms bonded together
• FuncHonally…
IonizaHon energy
• Recall: what is an ion? • IonizaHon energy is the energy required to remove an electron from a neutral atom and generate a caHon
• A + energy A+ + e-‐
• First ionizaHon energy is… • Second ionizaHon energy is…
Electron affinity
• Deals with acquisiHon of electrons by neutral atoms
• Electron affinity specifically is the energy change that results when an electron is acquired by a neutral atom
• A + e-‐ A-‐ + energy
Ionic radii
• What happens to the atomic radii when an atom is ionized? (hint: think about the dynamic between the nucleus and the electrons)
• What happens to the atomic radius when an atom acquires an electron?
A note on ions
• Electrons lost when an atom is ionized (becomes a ca.on) are generally always valence
• Electrons gained (resulted in the formaHon of an anion) will similarly become valence
• Example: generaHon of Fe3+
electronegaHvity
• The ability of the nucleus of an atom to a\ract electrons from other atoms
• Fluorine is arbitrarily assigned a value of 4, all other elements are given values based on this
• This explain why, for example, that water is a polar molecule.
11.17.11
• Can you believe it’s November 17 already?!?
• Today, MSFWBAT • Compete graphs of periodic trends, be ready to answer quesHons about periodic trends where your answers cite your data
• No ionic radii – why? But… • Check with me regarding your STEM fair topics • HW – p149 quesHons 1-‐5
Assignment #1
• graph the relaHonship between atomic number (z number) and each of the following: – IonizaHon energy (first and second ionizaHon energy) as well as electron affinity
– ElectronegaHvity and # of valence electrons – Atomic radii – Ionic radii
• For each, determine what the unit is, how it measured, what it means, and formulas that exist for it, and graph its value as a funcHon of atomic number
• Everyone makes their own graphs!
11.18.11
• Warmup: why is noble gas electronegaHvity typically zero?
• HW – p 164 #’s 1-‐3 (you already did #4!) • MSFWBAT • Explain trends across periods and down groups on the periodic table for electronegaHvity, atomic radius and ionizaHon energy
• IdenHfy characterisHcs of groups on the periodic table
Metals versus nonmetals
• Metals are things that are: – Shiny (reflect light) – Good conductor of heat/electricity – Tend to ionize easily and become caHons
• Non-‐metals are elements that are…not!
Group 1 – the alkali metals
• This is the lithium group. Som, silvery metals • Extremely reacHve, with low first ionizaHon energies • Low electronegaHvity • Conclusion – they tend to ionize easily and have their electrons captured by other elements
• Never found in nature as pure elements • Low melHng points for metals • React with nonmetals easily • Violently reacHve in water – liberate H2 gas which makes water alkaline
Group 2 – the alkali earth metals
• Harder than group alkali metals, contain ns2 electrons.
• Lowest second ionizaHon energies (though 1st IE is higher than group 1)
• Higher melHng points than group 1
• Less reacHve than group 1, but sHll never found as pure elements in nature
The transiHon metals
• A.k.a. the d block • Good conductors of electricity and heat, have high luster
• Less reacHve than group 1 and 2 elements
• Some so unreacHve that they do not form compounds (e.g. Pa, Pt, Au)
P block metals
• Bo\om lem corner of p block
• Generally, harder and denser than s-‐block metals, but less so than d-‐block metals
Metalloids (semi-‐metals)
• ProperHes intermediate between true metals and non-‐metals
• No universally agreed upon set of condiHons, only general trends
The gases
• Include the familiar gases such as Nitrogen, Oxygen, etc.
• React vigorously with metals (Oxygen causes Iron to rust, for example) forming salts
• Form anions, because they generally have high electronegaHvity and high ionizaHon energies
Halogens
• Group 17 elements • Capped by Flourine – the most electronegaHve element
• All very reacHve, in pure form all are toxic
Noble gases
• Chemically inert, they have full s and p subshells so do not take on electrons (generally)
• Very high ionizaHon energies – why? Full valence means stability, which means much more energy required to destabilize them
11.21.11
• Warmup: show me your notebook entry for November 18 (2 points HW)
• MSFWBAT
• IdenHfy regions of the periodic table • Explain the concept of shielding • ArgumentaHve essay on placement of He on periodic table – due 11.28
Review
• Describe the valence, electron affinity, electronegaviHty, and atomic radius of elements across periods, down groups
• What are the basic characterisHcs of each of the following: – Alkali metals – Alkali earth metals – TransiHon metals – P-‐block metals – Metalloids – Non-‐metals – Halogens – Noble gases
Nuclear shielding
• In general, increasing the atomic number increases the a\racHve force holding electrons to nuclei, but -‐
• The a\racHon (especially) valence electrons feel towards the nucleus (electrostaHc a\racHon) is diminished due to the effects of “buried” electrons
• Increasing energy levels increases the shielding effect
Chemical properHes of d and f block
• review: how many “valence” electrons in these elements?
• There is less variance and periodicity in the d and f blocks
• ProperHes of s and p block elements are determined almost enHrely be valence electrons
• TransiHon metals may form bonds using d block electrons
Periodic trends
• Atomic radii – d block radii generally decrease across periods, but much less so than across periods 2-‐3
• Why? (n-‐1)d sublevel electrons shield the outer electrons from the nucleus
• What do you expect for ionizaHon energy? • Going across a period IE goes up as expected • Going down, however, incomplete d subshells mean valence electrons are less shieled, so IE increases!
Note on ions
• Ionized electrons are always the highest level electrons, not the electrons you added last (Aurau)
• So the first and second ionizaHons for Fe are the 4s electrons, none of the 3d electrons
Lanthanides
• Trends follow similarly to d block for ionizaHon energy and atomic radius, with even less variance within the groups
• Consequently, these elements were all very difficult to isolate and idenHfy (they look, behave, and react very similarly to one another)
• SomeHmes called “rare earths” • All typically form +3 caHons
AcHnides
• Much more variance in valence than Lanthanides
• Thorium and Uranium are only acHnides that occur in any abundance
• ProtacHnium and Neptunium are transient
• All others are syntheHc • All are radioacHve
11.22.11
• Warmup: draw an orbital diagram for C, N and O and predict which one will have the lowest electron affinity
• MSFWBAT
• Argue for placement of He on periodic table
• (6th period – review Lanthanides and AcHnides)
Argument wriHng
• He is typically shown with the noble gas group, but should it be? Its configuraHon is 1s2, which indicates it could be considered among the alkali earths!
• Based on chemical and physical properHes, propose the ideal placement for Helium on the periodic table.
• 3 – 4 paragraphs. Should be typed. TNR 12-‐point double spaced. Include a data table/graph.
• Due 11.28