History of the periodic table

Mendeleev and Meyer arranged the elements

according to increasing atomic mass

• Mendeleev insisted that

the elements with similar

characteristics be listed in

the same families

• This left several blank

spaces in the table

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

http://www.bpc.edu/mathscience/chemistry/history_of_the_periodic_table.html

With such arrangement of the elements,

Mendeleev was able to predict the

properties of then unknown elements

Property

(of Germanium)

Mendeleev’s

Prediction

(1871)

Actual Value

(1886)

Atomic mass 72 72.59

Density, g/cm3 5.5 5.35

Color Dark gray Grayish white

Melting Point High 947

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

The periodic table arranged according to

increasing atomic mass had inconsistencies

• Ar, like the other noble gases, is

unreactive

• K, like the other elements in the first

column of the periodic table, is reactive

• Atomic mass of Ar (Z = 18) is greater than

that of K (Z = 19)

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

In a modern periodic table, the elements are

arranged according to increasing atomic number (Z)

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

The elements in a horizontal row of the

periodic table belong to the same period

• Properties of the element vary periodically

across the period

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

The elements in a column of the periodic

table belong to the same group or family

• Elements in the same group have

similar properties

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

The periodic table and

electron configuration

The electrons can be divided into categories

depending on the type of subshell being filled

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

ns

1

ns

2

ns

2n

p1

ns

2n

p2

ns

2n

p3

ns

2n

p4

ns

2n

p5

ns

2n

p6

d1

d5

d10

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

The outer electron configurations are similar

for elements belonging to the same group

Some atoms lose electrons so that the

resulting positively-charged species (cation)

will have a noble gas configuration

Na [Ne]3s1 Na+ [Ne]

Ca [Ar]4s2 Ca2+ [Ar]

Al [Ne]3s23p1 Al3+ [Ne]

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Electrons are always removed first from the

orbitals with the highest occupied principal

quantum number (n)

Li [He]2s1 Li+ [He]

Ga [Ar]4s23d104p1 Ga3+ [Ar]3d10

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

+1

+2

+3

Atoms belonging to the same group lose the

same number of electrons, hence they have

the same charge

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Some atoms gain electrons so that the

resulting negatively-charged species (anion)

will have a noble gas configuration

F 1s22s22p5 F- 1s22s22p6 or [Ne]

O 1s22s22p4 O2- 1s22s22p6 or [Ne]

N 1s22s22p3 N3- 1s22s22p6 or [Ne]

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Electrons are added first to an empty or partially

filled orbital with the highest available principal

quantum number (n)

F 1s22s22p5 F- 1s22s22p6 or [Ne]

Atoms belonging to the same group gain the

same number of electrons, hence they have

the same charge

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

-1

-2

-3

+1

+2

+3

Atoms belonging to the same group either gain or

lose the same number of electrons, depending which

mode is easier (note: their goal is to have the

configuration of a noble gas)

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

-1

-2

-3

Ions having the same electron configuration

and same number of electrons are said to

be isoelectronic

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Ion Electron

Configuration

Number of

Electrons

Na+ [Ne] 10

F- [Ne] 10

O2- [Ne] 10

N3- [Ne] 10

The periodic table and

classification of elements

The elements can either be a metal,

a nonmetal, or metalloid

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

lithium sodium

lead

Here are some examples of metals

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

Metals have the following properties

• Shiny luster

• Conduct heat and electricity

• Malleable (can be pounded into thin

sheets)

• Ductile (can be drawn into wire)

• All are solids at room temperature except

for mercury (which is a liquid)

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Here are some examples of nonmetals

carbon tellurium

chlorine

bromine

iodine

sulfur

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. Phils: Pearson Education Asia Pte. Ltd.

Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

phosphorus

Nonmetals have the following properties

• Not lustrous

• Poor conductors of heat and electricity

• Usually brittle; some are hard, and some are soft

• Some are gases (H2, N2, O2, F2, Cl2), one is a liquid (Br2), and one is a volatile solid (I2)

• The rest are solids that can be hard like diamond or soft like sulfur

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

Metalloids have properties intermediate

between those of metals and nonmetals

• i.e. silicon

– looks like a metal but is

brittle rather than

malleable

–Poorer conductor of heat

and electricity than

metals silicon

Brown, T., E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.