1. Dalton’s Atomic Theory
Atomic Structure
Dalton’s Atomic Theory
Dalton’s atomic theory explained that
■ All elements are made up of particles called atoms.
■ Atoms of one element are identical in size, mass, and chemical properties.

2. ■ Atoms of different elements have different masses and chemical properties.
■ Compounds are made up of atoms of different elements.
■ Atoms cannot be created or destroyed. They can be combined or rearranged in a chemical reaction.

3. Structure of atom Nucleus : Around nucleus :
consist of a) +ve charge protons
b) ± ve charge neutrons
Around nucleus :
-ve charge electrons

4. Atomic number “Z” :
It is the number of protons
Mass number “A”:
Number of protons + number of neutrons

5. Example Number of protons =11 Number of electrons = 11
Number of neutrons = = 12

6. Ions 1- Cation “ +ve charge” When atom lose electrons
2- Anion “-ve charge”
When atom gain electrons

7. Na+ Cl- 23 Number of protons =11 Number of electrons = 11-1=10 11
Number of neutrons = = 12 11 35
Number of protons =17
Number of electrons = 17+1=18
Number of neutrons = = 18 17

8. Isotopes
Atoms have the same atomic number but different in mass number (due to a different number of neutrons)
Example: three isotopes was exist to hydrogen
H , D (Deuterium), T(Tritium) 2 3 1 1 1 1

9. Practice problems: 1- in an atom tin-118
A- How many protons are there?
B- How many neutrons ?
C- How many electrons?
D- Write the symbol for tin-118.
E- How many electrons are in Sn+2
50p, 68n°, 50e Sn118
48e Sn+2

10. Identify the number of protons, neutrons, and electrons in the following.
1. 23Na+
2. 11B
3. 31P
4. 35Cl-

11. 3- Complete the following table (for uncombined isotopes):

12. The Elements and Periodic table
We have to know that all elements are arranged in Periodic table have the following:

13. It is constructed so that each vertical column contains elements that are chemically similar.

14. The elements in the columns are called groups, or families.
Elements in some groups can be very similar to one another.
Elements in other groups are less similar.

15. There are three distinct areas of the periodic table: 1-the main group elements, 2-the transition group elements, 3-the inner transition group elements
The periods and the groups are identified differently.
1- The periods are labeled from 1 to 7.
2- Groups are labeled with Arabic numerals from
1 through 18.