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Unit 5
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The Periodic Table & Periodic Law
Objective:▫Trace the development of the periodic table▫Identify key features of the periodic table
Development of the periodic table•- John Newlands
•- Meyer and Meedeleev
John Newlands
•1864 English chemist
• -Proposed a scheme for the elements
•-He noticed that when elements where arranged based on atomic mass their properties repeated every 8th element.
John Newlands
•-Newlands named the periodic relationship Law of octaves. (after a musical, a name which was frowned upon because it was unscientific)
•-Although not accepted Newland’s correct in the aspect that elements do repeat each other.
Meyer & Mendeleev
•Meyer-Russian chemist-1869 •Dmitri Mendeleev- 1869
▫Demonstrated a connection between atomic mass and elemental properties.
Meyer▫Demonstrated a connection between
atomic mass and elemental properties▫Arranged the elements in order of
increasing atomic mass
Mendeleev▫Demonstrated a connection between
atomic mass and elemental properties▫Arranged the elements in order of
increasing atomic mass▫Predicted the existence of properties of
undiscovered elements.
Mendeleev▫Mendeleev is given more credit.
▫ History of the Periodic Table
Periodic Table Activity▫Recognizing patterns
What did Mendeleev miss? ▫New elements were discovered, it became
evident that the periodic table was not in the correct order.
▫Henry Moseley (1887-1915), arrange elements by atomic number.
Moseley▫Discovered that atoms contain a unique
number of protons called the atomic number
▫Arranged element in order of increasing atomic number, which resulted in a periodic pattern of properties.
The Periodic Law
•Atoms with similar properties appear in groups or families (vertical columns) on the periodic table.
•They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.
The Periodic Table & Periodic LawElements & Modern periodic table
Modern Periodic Table
•Groups= columns “Vertical”
•Periods= rows “horizontal” ▫Periodic properties
Periods have similar characteristics.
Metals, Nonmetals, Metalloids
•How can you identify a metal?•What are its properties?•What about the less common nonmetals?•What are their properties?•And what the heck is a metalloid?
Alkali Metals
•Li•Na•K•Rb•Cs•Fr
Alkali Metals▫1 valance electron very reactive
Alkali metals with water
Alkali metals
▫Very reactive, often exists as compounds with other elements
▫Two familiar alkali metals are..Na- used in table saltLi- Used in batteries
Alkaline Earth
▫2 valance electron
▫Reactive-forms oxides
▫Important in living things Found on planet in raw forms
Halogens
▫Not “super” stable
▫7 valance electronsNeed 1 more
Halogens
Cl- HalogenUsed as a gas in WWI
Noble Gases ▫Most un-reactive
▫Why?8 valance electrons
Inert gases…▫Is a gas which does not undergo chemical
reactions under a set of given conditions
Mig welder- uses argon
CHNOPSS-nonmetals “important to life”
▫Carbon- that's what we are “made of”▫Hydrogen-your body is mostly H2O▫Nitrogen – amino acids▫Oxygen-energy out of food▫Phosphorous-DNA▫Sulfur-Protein▫Selenium –micro amounts/ a deficiency is thought to cause cancer
Nonmetals
•Nonmetals are the opposite.
•They are dull, brittle, nonconductors (insulators).
•Some are solid, but many are gases, and Bromine is a liquid.
Transition Metals ▫“weird” number of electrons
▫Cu-copper▫Au-Gold▫Ag-Silver
Titanium
▫Strong and light it is often used to make frames for bicycles and eyeglasses.
“Poor” metals
▫Al- Aluminum ▫Ga- Gallium ▫In – Indium ▫Sn-Tin▫Ti- thallium ▫Pb- lead▫Bi- Bismuth
“inner” transition metals ▫Actinide series
▫Lanthanide series used extensively as phosphors, substances
that emit light when struck by electrons
Metals▫Malleable & ductile, meaning they can be
pounded into thin sheets & drawn into wire
Metals met the nonmetals, forming a stair step on the right hand side of the periodic table.
Metals
•Metals are lustrous (shiny), malleable, ductile, and are good conductors of heat and electricity.
•They are mostly solids at room temp.
•What is one exception?
“The disappearing Spoon”
•Disappearing Spoon
Gallium Low melting point
Highly radioactive= good bye hand
Metalloids ▫B-Boron▫Si-Silicon▫Ge-Germanium▫As-Arsenic▫Sb-Antimony▫Te-Tellurium▫Po-Polonium▫At-Astatine
Metalloids•Metalloids, aka semi-
metals are just that.•They have characteristics
of both metals and nonmetals.
•They are shiny but brittle.•And they are
semiconductors.•What is our most
important semiconductor?
Metalloids▫Semiconductors▫Properties of both
metals and nonmetals.
Metalloids▫Two important
metalloids Ge-germanium Si-Silicon
Used in computers chips and solar cells
Metals, Nonmetals, Metalloids•There is a zig-zag
or staircase line that divides the table.
•Metals are on the left of the line, in blue.
•Nonmetals are on the right of the line, in orange.
Metals, Nonmetals, Metalloids• Elements that
border the stair case, shown in purple are the metalloids or semi-metals.
• There is one important exception.
• Aluminum is more metallic than not.
The Periodic Table & Periodic LawClassification of Elements
Objective:▫Explain why elements in the same group
have similar properties▫Identify the four block of the periodic table
based in their electron configuration
Valence Electrons
•Do you remember how to tell the number of valence electrons for elements in the s- and p-blocks?
•How many valence electrons will the atoms in the d-block (transition metals) and the f-block (inner transition metals) have?
•Most have 2 valence e-, some only have 1.
Valance electrons
Electron configuration
s, p, d, and f blocks
The Periodic Table & Periodic LawPeriodic Trends
Definition: Half of the distance between nuclei in covalently bonded diatomic molecule Radius decreases across a period
Increased effective nuclear charge due to decreased shielding
Radius increases down a group Each row on the periodic table adds a “shell” or energy level to the atom
Atomic Radius
Table of Atomic Radii
Explanation Video-Atomic Radii
Period Trend:Atomic Radius
Tends to increase across a period As radius decreases across a period, the electron you are removing is closer to the nucleus and harder to remove
Tends to decrease down a group Outer electrons are farther from the nucleus and easier to remove
Ionization Energy Definition: the energy required to remove an electron from an atom
Periodic Trend:Ionization Energy
ElectronegativityDefinition: A measure of the ability of an atom in a chemical compound to attract electronso Electronegativity tends to increase across a periodo As radius decreases, electrons get closer to the bonding atom’s nucleus
o Electronegativity tends to decrease down a group or remain the sameo As radius increases, electrons are farther from the bonding atom’s nucleus
Periodic Table of Electronegativities
Periodic Trend:Electronegativity
Summary of Periodic Trends
Ionic Radii
Cations
Positively charged ions formed when an atom of a metal loses one or more electrons Smaller than the corresponding atom
Anions
Negatively charged ions formed when nonmetallic atoms gain one or more electrons
Larger than the corresponding atom
The Octet Rule•The “goal” of most atoms (except H, Li
and Be) is to have an octet or group of 8 electrons in their valence energy level.
•They may accomplish this by either giving electrons away or taking them.
•Metals generally give electrons, nonmetals take them from other atoms.
•Atoms that have gained or lost electrons are called ions.
Ions
•When an atom gains an electron, it becomes negatively charged (more electrons than protons ) and is called an anion.
•In the same way that nonmetal atoms can gain electrons, metal atoms can lose electrons.
•They become positively charged cations.
Ions•Here is a simple way to remember which
is the cation and which the anion:
This is a cat-ion.
This is Ann Ion.
He’s a “plussy” cat!
She’s unhappy and negative.
+ +
Ionic Radius
•Cations are always smaller than the original atom.
•The entire outer PEL is removed during ionization.
•Conversely, anions are always larger than the original atom.
•Electrons are added to the outer PEL.
Cation Formation
11p+
Na atom
1 valence electron
Valence e- lost in ion formation
Effective nuclear charge on remaining electrons increases.
Remaining e- are pulled in closer to the nucleus. Ionic size decreases.
Result: a smaller sodium cation, Na+
Anion Formation
17p+
Chlorine atom with 7 valence e-
One e- is added to the outer shell.
Effective nuclear charge is reduced and the e- cloud expands.
A chloride ion is produced. It is larger than the original atom.
Graphic courtesy Wikimedia Commons user Popnose
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