Page 6 - Science E-Book Prep.2 2024-2025 1st term_Neat - Copy

Isotopes :-they are element have different atomic weight
and same atomic number

2- Moseley’s periodic table

At this time, scientist Rutherford discovered that
nucleus contains positively charged protons

.
Moseley’s modifications on Mendeleev’s table:
1. He arranged elements in an ascending order
according to their atomic number not
atomicweight.
2. He added zero group for inert gas (noble gas)
3. He classified each group into to subgroups
(A&B) according to the similarity in their
properties.
4. He specified a place below the table for
lanthanides and actinides elements

Notes:
Bohr discovered that atom has energy levels,
their number is 7 in the heaviest atom.

2nd Prep. First Term 6