Chemistry-Atomic Structure

The proton number and the nucleon number
1. An atom is made up of three sub-atomic particles, neutrons, electrons and protons.
2. Sub-atomic particles differ in mass and electric charge.

Sub-atomic particle	symbol	Relative mass	Relative charge
Proton	P	1	+1
Neutron	N	1	0
Electron	E	1/840	-1

3. Proton number, Z=number of protons

4. Nucleon number, A= total number of protons and neutrons

5. Number of neutrons, A-Z

6. An atom is electrically neutral. This means that in an atom, the number of protons is the same as the number of electrons.

Isotopes

1. Isotopes are atoms with the same number of protons and electrons.

2. Isotopes have the same chemical properties, but slightly different physical properties.

3. Electrons are arranged in electron shells.

4. The first electron shell can hold up to 2 electrons, the second and third usually hold up to 8 electrons.

5. The way in which the electrons are arranged in electron shells is called the electronic structure or the electronic configuration of the atom.

6. Valence electrons are electrons found in the outer shell of the atom. They are important because they affect the chemical properties of an element.

Output:

1. Mass number = no. of protons+no. of neutrons

2. No. of proton = atomic number

3. Proton+neutron = mass number

4. electronic configuration shows the number of electrons

5. Valence is the outermost electron shell.

6. Isotopes --> same number of protons, different neutrons. different in mass number because mass number = no. of protons+no. of neutrons

7. Ion: atom/molecule in which total number of electrons is not equal to protons.

8. Positive ions: Less electrons compared to protons

9. Negative ions: More electrons compared to ions