1. Atomic Structure

2. What is an atom?
Atom: the smallest unit of matter that retains the identity of the substance
First proposed by Democritus

3. Atomic Structure Atoms are composed of 2 regions:
Nucleus: the center of the atom that contains the mass of the atom (majority)
Electron cloud: region that surrounds the nucleus that contains most of the space in the atom
Nucleus
Electron
Cloud

4. What’s in the Nucleus?
The nucleus contains 2 of the 3 subatomic particles:
Protons: positively charged subatomic particles
Neutrons: neutrally charged subatomic particles

5. What’s in the Electron Cloud?
The 3rd subatomic particle resides outside of the nucleus in the electron cloud
Electron: the subatomic particle with a negative charge and relatively no mass

6. How do these particles interact?
Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom

7. How do these particles interact?
The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

8. Relative Weights of Sub-Atomic Particles

9. How do the subatomic particles balance each other?
In a neutral atom:
The protons equal the electrons
If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral
The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

10. How do we know the number of subatomic particles in an atom?
On the Periodic Table
Atomic Number
Symbol
Name
Atomic Mass
(Mass Number)

11. How do we know the number of subatomic particles in an atom?
Atomic number: this number indicates the number of protons in an atom
Ex: Hydrogen’s atomic number is 1
So hydrogen has 1 proton
Ex: Oxygen’s atomic number is 8
So oxygen has 8 protons
**The number of protons identifies the atom.
Ex. 29 protons = which element???

12. How do we know the number of subatomic particles in an atom?
Atomic #- 8 (protons)
Mass #: the number of protons and neutrons in the nucleus
Ex: oxygen has a mass of 16.
# of neutrons =
mass # - atomic #
Since it has 8 protons it must have 8 neutrons
(16-8)

13. Determining the number of protons and neutrons
Li has a mass number of 7 and an atomic number of 3
Protons = 3 (same as atomic #)
Neutrons= 7-3 = 4 (mass # - atomic #)
Ne has a mass number of 20 and an atomic number of 10
Protons = 10
Neutrons = = 10

14. What about the electrons?
The electrons are equal to the number of protons
So e- = p = atomic #
Ex: O has a mass # of 16 and an atomic # of 8
p+ = 8
no = 8
e- = 8

15. Determine the number of subatomic particles in the following:
Cl has a mass # of 35 and an atomic # of 17
p+ = 17,
no = 18,
e- = 17
P+ = 19,
no = 20
e- = 19

16. How exactly are the particles arranged?
Bohr Model of the atom: Electron levels
All of the protons and the neutrons
The 3rd ring can hold up to 18 e-
The 1st ring can hold up to 2 e-
The 4th ring and any after can hold up to 32 e-
The 2nd ring can hold up to 8 e-

17. What does carbon look like?
Mass # = 12 atomic # = 6
p+ = 6 no = 6 e- = 6
The second electron shell can hold how many electrons? 8
Carbon has four of the 8 .
6 p and 6 n live in the nucleus
Therefore, carbon has 4 VALENCE ELECTRONS (the # of electrons found in the outermost shell)

18. Your Turn Bohr Models Hydrogen Beryllium Nitrogen
1 valence valence valence

19. A quick word about ions
Ions- a charged particle that forms when an atom (or group of atoms) gains or loses one or more electrons.
+ Ions: have lost one or more electrons
- Ions: have gained one or more electrons

20. Some examples…

21. …and some jokes