The History The History of the of the

Modern Modern Periodic Periodic

TableTable

During the nineteenth During the nineteenth century, chemists century, chemists

began to categorize the began to categorize the elements according to elements according to

similarities in their similarities in their physical and chemical physical and chemical properties. The end properties. The end

result of these studies result of these studies was our modern was our modern periodic table.periodic table.

DmitriDmitri MendeleevMendeleev

1834 - 1834 - 19071907

In 1869 he published In 1869 he published a table of the a table of the elements organized elements organized by increasing atomic by increasing atomic mass.mass.

• Mendeleev left blank spaces in his table

• The existence of unknown elements was predicted by Mendeleev on the basis of the properties of the blank spaces.

• When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements.

After the discovery of these After the discovery of these unknown elements between unknown elements between 1874 and 1885, and the fact 1874 and 1885, and the fact that Mendeleev’s that Mendeleev’s predictions for Sc, Ga, and predictions for Sc, Ga, and Ge were amazingly close to Ge were amazingly close to the actual values, his table the actual values, his table was generally accepted.was generally accepted.

Periodic LawPeriodic LawWhen elements are When elements are arranged in order of arranged in order of increasing atomic number, increasing atomic number, there is a periodic pattern in there is a periodic pattern in their physical and chemical their physical and chemical properties.properties.

The periodic table is the The periodic table is the most important tool in the most important tool in the

chemist’s toolbox!chemist’s toolbox!

Trends on the Trends on the Periodic TablePeriodic TableBrainiacBrainiac: Alkali Metals: Alkali Metals

Groups and PeriodsGroups and Periods

Groups or Families - a column of elements on the periodic table. There are 18 groups on the table

Period - a row of elements on the periodic table. There are seven periods on the table

Groups and PeriodsGroups and Periods

You need to know five family You need to know five family names and locationsnames and locations

1

2

3-12

17

18

Properties of FamiliesProperties of FamiliesAlkali metals (1)—The most reactive metal family,

must be stored under oil because they react violently with water! They dissolve and create an alkaline, or basic, solution, hence their name.

Alkaline earth metals (2)—These also are reactive metals, but they don’t explode in water; pastes of these are used in batteries.

Halogens (17)—Known as the “salt formers,” they are used in modern lighting and always exist as diatomic molecules in their elemental form.

Noble gases (18)—Known for their extremely low reactivity, these were once thought to never react; neon, one of the noble gases, is used to make bright signs.

Periodic Table and Electron Periodic Table and Electron ConfigurationsConfigurations

Elements in the same group have the same outer shell electron configuration so they have similar chemical properties.

S

dp

f

Metals, Nonmetals, Metals, Nonmetals, MetalloidsMetalloids

• 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, Metals, Nonmetals, MetalloidsMetalloids

• 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.

MetalsMetals• 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?

NonmetalsNonmetals• Nonmetals are the

opposite.• They are dull,

brittle, nonconductors (insulators).

• Some are solid, but many are gases, and Bromine is a liquid.

MetalloidsMetalloids• Metalloids, aka semi-

metals are just that.• They have

characteristics of both metals and nonmetals.

• They are shiny but brittle.

• And they are semiconductors.

The Three Main Groups of The Three Main Groups of Elements on the Periodic TableElements on the Periodic TableMetals• luster (shine) • good conductors of heat and electricity • solid at room temperature • most are malleable and ductile

Non-metals • Dull, not shiny• poor conductors of heat and electricity • neither malleable or ductile • many are gasses at room temperature

Semimetals or metalloids    • have some properties of metals and some of non-metals

Trends on the Periodic TableTrends on the Periodic TableAtomic Radius – the size (diameter)

of the atomDecreases as you go across a period,

but increases as you go down a group.Ionization energy – the energy

required to remove a valence electron. (outer most electron)Increases as you go across a period, but

decreases as you go down a group.

TrendsTrendsIncreasing ionization energy

Dec

reas

ing

Io

niz

atio

n E

ner

gy

Why the Trend in Atomic Why the Trend in Atomic Radius?Radius?

Across a period the radius decreases-• As you go from left to right the protons in

the nucleus increase and the electrons also increase which causes the atom to be 'sucked' together a little tighter.

Down a group radius increases - • A new energy level of electrons is added to

the atom as you go down each row, making each atom significantly larger.

Why the Trend in Ionization Why the Trend in Ionization EnergyEnergy??

Increases as you go across a group because the elements are getting smaller and the electrons are closer to the nucleus making it harder to remove an electron.

Decreases as you go down a column because the electrons are further from the nucleus and easier to remove. (lower ionization energy)

Ionic sizeIonic size• Metallic elements easily lose

electrons.• Non-metals more readily gain

electrons.

How does losing or gaining an electron effect the size of the atom (ion) ?

Positive ionsPositive ions• Positive ions are always smaller that

the neutral atom. Loss of outer shell electrons.

Negative IonsNegative Ions• Negative ions are always larger than

the neutral atom. Gaining electrons.

Number of protons

Charge = protons - electrons

Ion size trends in columns.Ion size trends in columns.• Ion size increases

as you move down a column for both positive and negative ions