PeriodicTable

History of the Period Table• The first periodic table was

devised by Dmitri Mendeleev and published in 1869.

• Mendeleev found he could arrange the 65 elements that were then known in a grid or table so that each element had:– A higher atomic weight than the

one on its left.– Similar chemical properties to

other elements in the same column.

Mendeleev‘s Table• He realized that the table lay

at the very heart of chemistry. In his table he noted gaps - spaces where elements should be but none had yet been discovered.

• Mendeleev discovered germanium, gallium and scandium for he predicted their existence and their properties before their actual discoveries.

• Although Mendeleev had made a crucial breakthrough, he made little further progress because the Rutherford-Bohr model of the atom had not yet been formulated.

Mendeleev‘s Table

Rutherford‘s C• Ernest Rutherford, a renowned nuclear physicist worked on

charged particles in the early 1900’s.  Developed the atomic model that we used today to describe atoms.

• A. van den Broek and Henry Moseley used x-rays to study the atomic structure. 

• In 1913 they used X-rays to determine the number of protons in an atom.  

• He also recognized that the atomic number (number of protons) was more reliable in ordering the elements in the periodic tables.   

• He arranged the new table with increasing atomic number, which allowed a more predictive quality of the periodic table than ranking them by atomic weight (mass number).

Today‘s Periodic Table

Atomic Number and Mass Number

• Atomic number is the number of protons in an atom.

• Mass number is the number of protons and neutrons in an atom.

The structure of the Atom• Atom are made of protons, neutrons and electrons.• The nucleus contains the protons and neutrons. • Electrons orbit the nucleus.• Virtually all the mass of an atom is in the nucleus because the

electron weighs hardly anything.• Masses are measured relative to each other as the numbers are so

small (there would be 600000000000000000000000 protons in 1g)

Charge = +1

Mass = 1

Charge = 0

Mass = 1

Charge = -1

Mass = 1/1836

Activity

• Use the periodic table to find the atomic numbers of the following elements;– Flourine– Hydrogen– Helium

• Explain what the mass number means.• Write down the number of protons,

neutrons and electrons in the above elements.

Homework

• Create our own periodic table.• Each student has to prepare 2 A5 size

elements.Must contain:

Name

Symbol

Mass number

Atomic number

Description (2 sentences)

Can contain a picture

The periodic tableAll the known elements are shown in the periodic table.

Can you spot any patterns in how the elements are arranged in the periodic table?

Who invented the periodic table?

How are the elements arranged?The elements in the periodic table are arranged in families called groups and

periods. A group is a vertical column in the periodic table; a period is a horizontal row.

For example, all the elements in group 0 are very unreactive gases at room temperature, while all the elements in group 1 are very reactive metals.

The elements in groups tend to have similar properties.

groups 0 to 7pe

riods

1 to

6

Solids, liquids and gasesWhy are some symbol names in the periodic table, below, shown in different colours? (clue: think about group properties)

Bromine and mercury are liquids at room temperature; all the other elements are solids or gases.

MetalloidsMetals are on the left and in the centre of the periodic table.

Non-metals are located mostly on the right.

Metalloids sometimes behave like metals and sometimes like non-metals.

Silicon and germanium are examples of metalloids.

Metalloids are located between metals and non-metals in the periodic table.