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Friday 12/04/15
Objectives Understand the general trends in atomic
properties in the periodic table Understand the nature of bonds and their
relationship to electronegativity
Reading the periodic table
Groups or families – vertical columns
Periods – horizontal rows
Term Effective Nuclear Charge (ENC) 1) The net charge that pulls on the valence electrons in an
atom. The greater the effective core charge, the greater the pull. It is determined by subtracting the number of core electrons from the number of protons in the nucleus For example: Magnesium
Periodic Trends
Atomic radius The distance from the center of an atoms nucleus to it’s outermost electron
Measure of atomic size
Periodic Trends Graph the first 20 elements. What is the trend down a group? Across a Period?
Atomic radius
Periodic Trends
Atomic Radius Group Trend
Increases down a group More energy levels or quantum levels (or “shell”) as
you go down a group – atomic radius increases Period Trend
Decreases across a period All electrons in the same energy level. Increased # of
protons holds them closer to nucleus. Increase in Effective Core (Nuclear) Charge (ECC)
Calculate ECC for elements in period 2
Table of Table of Atomic Atomic RadiiRadii
Period Period Trend:Trend:Atomic Atomic RadiusRadius
Periodic Trends Worksheet
Work with a table partner to answer questions:1,5a, 6, 8,
Periodic Trends
Ionic Size
Size of an atom when electrons are added or removed.
Electrons removed atom becomes smaller.
Electrons added atoms become larger
Why? Electron-Electron
Repulsion
Ionic SizeIonic Size
CationsCations
Positively charged ions formed when an atom of a metal loses one or more electrons Smaller than the corresponding atom
AnionsAnions
Negatively charged ions formed when nonmetallic atoms gain one or more electrons
Larger than the corresponding atom
Periodic TrendsGraph the first 20 elements. What is the trend down a group? Across a Period? Ionic Size (label P.T.)
Table of Table of Ion Ion SizesSizes
Ionic Size
Group Trend Increases down a group More energy levels as you go down a group – ionic
size increases Period Trend
Decreases as atoms lose more electrons Increases dramatically as atoms start gaining
electrons, decreases as atoms gain fewer electrons.
Periodic Trends
Ionization Energy Energy needed to remove one of the electrons on an atom’s outer shell.
How strongly does an atom hold it’s outermost electron.
Periodic Trends Graph the first 20 elements. What is the trend down a group? Across a Period?
Ionization Energy
Ionization Energy Group Trends
Increases up a group.The closer outer shell electrons are to the
nucleus the harder they are to remove. Period Trend
Increases across a period.The more electrons in the outer shell the harder
it is to remove one. Increase in Effective Core Charge (ECC)
Periodic Trend:Periodic Trend:Ionization EnergyIonization Energy
Periodic Trends Worksheet
Work with a table partner to answer questions:3, 5b, 7, 9
Periodic Trends
Electronegativity Is a measure of the level of attraction (pull) an atom exerts on the electrons of another atom.
Ability of an atom to attract electrons
Which elements want to gain electrons the most?
Periodic TrendsGraph the first 20 elements. What is the trend down a group? Across a Period? Electronegativity
Periodic Table of ElectronegativitiesPeriodic Table of Electronegativities
Electronegativity Group Trend
Increases up a groupAs radius decreases, electrons are closer to the
nucleus (decrease in number of electron shells) Period Trend
Increases across a periodThe more electrons in the outer shell (up to 7)
the more the atom wants to attract electrons Exception: Trend does not apply to Noble Gases
Increase in Effective Core Charge (ECC)
Periodic Trend:Periodic Trend:ElectronegativityElectronegativity
Periodic Trends Worksheet
Work with a table partner to answer questions:2, 4, 5c, 10, 11
Summary of Summary of Periodic TrendsPeriodic Trends
Practice
1. Se and Br1. Smallest atom
2. Lowest Ionization Energy
2. P, S, Se1. Largest atom
2. Highest Ionization Energy
3. Cl, Cl1-, Br, Br1-
1. Largest ionic size
4. Mg, Mg2+, Na, Na1+
1. Smallest ionic size
Atomic Properties DefinitionsFor Quiz – Monday Effective Nuclear Charge:
It is the net charge that pulls on the valence electrons in an atom.
The greater the effective nuclear charge, the greater the pull.
It is determined by subtracting the number of core electrons from the number of protons in the nucleus
Valence Electrons Are found in the outermost, valence, electron shell
(Bohr model) of the atom Core electrons
occupy all of the inner electron, core, shells
Atomic Properties Definitions Ionization Energy:
Energy needed to remove an electron from an atom or molecule. The higher the effective core charge and lower the number of
electrons shells, the greater the ionization energy Atomic size
How big (e.g., radius) an atom is Atomic radius is measured from the center of the nucleus to the
valence electron shell. The higher the effective core charge and lower the number of
electron shells, the smaller the atom. Electronegativity
Measure of the level of attraction (pull) an atom exerts on the electrons of another atom.
The higher the effective core charge and lower the number of electron shells, the greater the electronegativity
Homework
Read pages:327-331
Answer questions: Pg 336 69-78
343-345 Answer questions: Pgs 374-375, 7-20
Due 12/09
Periodic TableObjective: Students know how to use the periodic table to identify alkali metals, alkaline earth metals, transition metals, metals, semimetals (metalloids), nonmetals, halogens and noble gases.
Alkali Metals All alkali metals have 1
valence electron They are very reactive Reactivity of these elements
increases down the groupAlkali metals:
http://video.google.com/videoplay?docid=-2134266654801392897#
Potassium, K reacts with water and must be stored in kerosene
Alkaline Earth Metals All alkaline earth metals have 2 valence
electrons Alkaline earth metals are less reactive than
alkali metals The word “alkaline” means “basic”
common bases include salts of the metals Ca(OH)2
Mg(OH)2
Properties of MetalsProperties of Metals Metals are good conductors of heat and electricity
Metals are malleable
Metals are ductile
Metals have high tensile strength
Metals have luster
Transition Transition MetalsMetals
Copper, Cu, is a relatively soft metal, and a very good electrical conductor.
Mercury, Hg, is the only metal that exists as a liquid at room temperature
Properties of Metalloids They have properties of both metals and nonmetals.Metalloids are more brittle than metals, less brittle than most nonmetallic solids Metalloids are semiconductors of electricity Some metalloids possess metallic luster
Silicon, Si – A MetalloidSilicon, Si – A Metalloid Silicon has metallic luster Silicon is brittle like a nonmetal Silicon is a semiconductor of electricity
Other metalloids include:
Boron, B Germanium, Ge Arsenic, As Antimony, Sb Tellurium, Te
NonmetalsNonmetals Nonmetals are poor conductors of heat and electricity Nonmetals tend to be brittle Many nonmetals are gases at room temperature
Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element.
Examples of NonmetalsExamples of Nonmetals
Sulfur, S, was once known as “brimstone”
Microspheres of phosphorus, P, a reactive nonmetal
Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure
HalogensHalogens Halogens all have 7 valence electrons
Halogens in their pure form are diatomic molecules (F2, Cl2, Br2, and I2)
Chlorine is a yellow-green poisonous gas
Noble GasesNoble Gases
Noble gases have 8 valence electrons (except helium, which has only 2)
•they are chemically unreactive
• Colorless, odorless and unreactive; they were among the last of the natural elements to be discovered