1. The Atom

2. The Atom
The atom has three parts:
Protons
Neutrons
Electrons

3. 1 PROTON = 1 POSITIVE Charge
Protons
Protons:
Found in the nucleus
Mass: one (1) Atomic Mass Unit
have a (+) positive charge,
1 PROTON = 1 POSITIVE Charge

4. Protons (Cont’d)
On the periodic table, each element is numbered. This number equals the number of Protons in the nucleus.

5. Neutrons Also found in the nucleus. Mass: one (1) Atomic Mass Unit.
They have NO charge. Neutron = Neutral

6. Electrons Found around the nucleus (like planets around the Sun)
An Electron’s mass is almost nothing…almost
Have a negative (-) charge
ELECTRONS = NEGATIVE

7. Standard Atomic Notation
Mass Number = mass of all the protons and neutrons in the nucleus 9 Be
Element Symbol – eg. Beryllium 4
Atomic Number = number of protons in the nucleus and the number of electrons orbiting the nucleus
To find the number of neutrons in the nucleus, subtract atomic number from mass number. There would be 9 – 4 or 5 neutrons in a Beryllium atom

8. Remember
The periodic table is organized by atomic number (the number of protons the element has in its nucleus)
Protons are + and electrons are -
The number of protons = the number of electrons (positives = negatives)

9. Let’s try some! Have your periodic table ready
How many protons, neutrons and electrons in one atom of:
Hydrogen?
Carbon?
Beryllium?
Calcium?
Fluorine?
1 p+, 1 e-, 0 n
6 p+, 6 e-, 6 n
4 p+, 4 e-, 5 n
20 p+, 20 e-, 20 n
9 p+, 9 e-, 10 n

10. Bohr Rutherford Diagrams

11. Bohr-Rutherford Diagrams
Named after the work done by Neils Bohr and Ernest Rutherford (nobody before them gets any respect!)
Flattened model of the inside of an atom
Unique for each atom

12. Electron Shells
First Shell, maximum 2 electrons

13. Why only 2 in the first shell?
2 elements in first row (period)

14. Electron Shells
Second Shell,
Maximum 8 electrons

15. Why 8 in the second shell?
8 elements in second period

16. Electron Shells Third shell, max # 8 electrons
Note: Magnesium only needs 2 electrons in this shell because it has 12 total

17. Bohr-Rutherford Diagrams
Eg. Magnesium

18. Guess this element
82 protons = element 82 which is LEAD

19. The Noble Gases
Column to the far right of the periodic table, He, Ne, Ar, Kr, Xe, & Rn

20. So, how would Magnesium look like Neon?

21. So, if Mg lost two Electrons, but still had the same number of Protons, what is its Charge?+2

22. Charges The outer electrons on an atom are called: Valence electrons.
Atoms want a Bohr-Rutherford Diagram that look like the Noble Gases because…
have the most stable structure
Won’t react when mixed
Usually, this means the atom ends up with a Charge.

23. Fluorine - 1 What does F need to look like a Noble gas?
If we add one Electron, what will the Charge of the atom be?
- 1

24. Ions
Ion= a Charged atom in which the number of ELECTRONS (-) is different from the number of PROTONS (+).
Ionic Charge= is the number of positive (+) or negative (-) Charges on an atom. Ex: Mg+2

25. Groups Mg
Be (Berylium)

26. So…
Even though each element has a different # of PROTONS and ELECTRONS, each element in a group has a similar Bohr-Rutherford Diagram
This means they want to gain or lose the same number of Electrons.
It also means elements in a Group will react similarly in Chemical Reactions