the periodic table & periodic law

The Periodic Table & Periodic Law

Objective:▫Trace the development of the periodic table▫Identify key features of the periodic table

•Sheldon & The Element Song

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

•Element Song

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