Structure of Atoms & Periodic Table | Grade 9 Lessons

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.

🧪 Classify the Element

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.

🔬 Atomic Model Timeline

Tap to see how atomic models evolved over time:

🧠 Match the Model to the Scientist

Click to match each atomic model with its scientist:

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.

Periodic Table Grid

Here’s a simplified periodic layout:

🎯 Guess the Element

Guess the element from its symbol:

Symbol: H

🧠 Quiz: Test Your Knowledge