1. Electrons and the Atom
SCh3U/4C
Ms. Richardson

2. Refining the Atomic Model
Bohr’s work provides information about energy levels at which electrons can exist
We can also determine how many electrons exist in each energy level:
# electrons in a shell = 2n2
Where n is the number of the shell

4. Electrons of the Atom
When a shell contains the maximum number of electrons, it is said to be filled.
Electrons in the outer shell of an atom are known as valence electrons and the shell is the valence shell.
The valence electrons are the only electrons involved in forming chemical bonds

5. Lewis Diagrams and Electrons
Lewis diagrams are simplified models used to represent atoms.
To draw the Lewis diagram for an atom, we write the chemical symbol and place the valence electrons around the symbol

6. Lewis Diagrams (continued)
Always place electrons at “N, S, E, W” before doubling up.

7. Lewis Diagrams (continued)
Pairing dots when drawing Lewis diagrams for an atom with more than four valence electrons is important.
These electron pairs are less likely to participate in bonding than unpaired/lone electrons

8. The Nucleus
Rutherford discovered that the nucleus occupies the centre of the atom as well as many other features of the nucleus

9. Protons & Neutrons
The nucleus is where the mass of the atom is located, comprised of the protons and neutrons.

10. Neutrons & Isotopes
The atomic number represents the number of protons in an atom
This also indicates the number of electrons for a neutral atom
The number of neutrons in the nucleus of atoms of the same element can vary, as seen with isotopes

11. Isotopes
Isotopes are atoms of the same element that have different number of neutrons
This results in a different mass number for the isotope
Eg: Carbon-12 and Carbon-14
6 neutrons 8 neutrons

12. Isotope Notation
When representing isotopes, we still use standard atomic notation
We can also represent them by naming the element and indicating the mass number
Eg: carbon-14, nitrogen-15

13. Determining Number of Neutrons
To find the number of neutrons in an element/isotope, we can use the formula:
# of neutrons = atomic mass – atomic number