Structure of Atoms & Periodic Table.
The smallest components of any matter are atoms. The world around us is composed of the atoms - the air, the water, our body and all the rest. The knowledge of their structure will teach us how elements work and are arranged in the Periodic Table.
1. Elements
What Are Elements?
Elements are pure substances which contain only one kind of atom.
Examples of Elements:
H, O, C, and Fe.
Importance:
Each of the elements is distinct and combines with others to create compounds.
2. Atomic Models
Atomic models enable us to visualize the structure atom. Over several years, scientists have come up with various models.
Dalton’s Model (1803):
Suggested that it is a particle that cannot be divided.
Thomson’s Model (1897):
Proposed that atoms consist of a positively charged "pudding" with negatively charged electrons scattered in it.
Rutherford’s Model (1911):
Found that atoms have compact nucleus with electron travelling in orbits around it.
Bohr’s Model (1913):
Advocated Electron orbital motion of the nucleus in a fixed motion or energy levels.
Modern Quantum Model:
States that electrons are located in the regions of probability surrounding the nucleus, which are called orbital.
3. Trends in the Periodic Table
The Periodic Table is an arrangement where elements are organized on the basis of atomic number and their properties. Some key trends include:
Atomic Size:
Atoms increase in size going down the groups and decrease going across a period left to right.
Ionization Energy:
The energy needed to take away an electron increases on a period and decreases along a group.
Electronegativity:
The power of attraction of an atom towards the electrons increases during a Period and decreases on moving down a group.
Metallic to Non-metallic Character:
Through the movement along a period from left to right, elements tend to become less metallic and more non-metallic.