1. Atoms: Building Blocks of Matter

2. Nucleus: made up of protons and neutrons in center of atom
Structure of an Atom
Subatomic particles: 3 particles that make up an atom (protons, neutrons, electrons)
Nucleus: made up of protons and neutrons in center of atom
Proton: positively charged particle
Neutron: particle with no charge

3. Structure of an Atom
Electrons: negatively charged particles around the nucleus
All protons are alike, all neutrons are alike, and all electrons are alike even in different substances!

4. Greek Model: original idea of matter made of particles
Atomic Models
Greek Model: original idea of matter made of particles
Atomos:
“not to be cut”
or indivisible

5. Atomic Models John Dalton Model: 1803
All elements (gold, silver, hydrogen, oxygen,…) are made of atoms

6. Atomic Theory and Models
Dalton thought that atoms were like smooth, hard spheres that could not be broken into smaller pieces.

7. Atomic Models Dalton Model:
Atoms of the same element are exactly alike
Atoms of different elements are different

8. Atomic Models Dalton Model: Compounds: formed by the joining
of atoms of 2 or more elements

9. J.J. Thomson and his cathode ray experiment 1897

10. Atomic Theory and Models
Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.
Also known as the “plum pudding” model

11. Ernest Rutherford’s Gold Foil Experiment 1908

12. Most of the particles went directly through the foil!

13. Atomic Theory and Models
Rutherford was surprised that only a few positive particles were deflected strongly. This led him to conclude that atoms had positively charged particles in the nucleus.

14. Atomic Theory and Models
Since many particles passed right through the foil sheet, he also concluded that the atom must have a lot of space separating the nucleus from the electrons.

15. Atomic Theory and Models
Through the early twentieth century, atomic models continued to change.
Niels Bohr Model: 1912
Niels Bohr suggested that electrons move in specific orbits around the nucleus of an atom

16. Atomic Theory and Models
Cloud Model: 1927
Electrons move rapidly in every direction around the nucleus

17. Atomic Theory and Models
Modern Atomic Model:
The nucleus, which contains both protons and neutrons, is surrounded by a cloudlike region of electrons.

18. Let's see what Tim and Moby have to say about Atomic Models

19. Design of periodic table
Periodic Table: A classification system for elements
Atomic number 79
Au chemical symbol
Gold
common name
Atomic mass

20. Characteristics of Atoms
Atomic Number: number of protons in each element
Hydrogen = Helium = 2
Oxygen = Nitrogen = ___
Look at periodic table of elements in your agenda or on the back cover of your book

21. Characteristics of Atoms
AMU: special unit to measure the mass of atoms
One proton = one AMU
One neutron = one AMU g
Electrons have no mass g

22. Using your periodic table, answer the following.
How many protons does Krypton have?
a) 84 b) 36 c) 83 d) 48
How many electrons does Krypton have?
a) 84 b) 36 c) 83 d) 48
How many neutrons does Krypton have?
a) 84 b) 36 c) 83 d) 48

23. Using your periodic table, answer the following.
How many protons does Silver have?
a) 107 b)61 c) 108 d)47
How many electrons does Silver have?
a) 107 b)61 c) 108 d)47
How many neutrons does Silver have?
a) 107 b)61 c) 108 d)47

24. Electrons Each electron is in an energy level
The higher the energy level = the farther the distance from the nucleus
Inside level holds 2 electrons
The 2nd level holds 8 electrons
The 3rd level holds 8 electrons (it CAN hold 18)
The number of electrons in the outer “shell” or “orbit” determines how it will act and react to other substances

25. Drawing Bohr Models of the Atom
Remember the Bohr Model?
Even though the “Cloud” model is the most accurate, we cannot diagram atoms easily in 3-D.
We use Bohr’s model to illustrate which energy levels the electrons are located in.

26. Examples of Bohr Diagrams
Sodium
Which element?
Build a Bohr Diagram

28. Atom Game Each person represents a subatomic particle:
Proton = Red Neutron = Blue
Electron = Yellow
In your group, please construct the following atoms – help each other!
- Oxygen – O Sodium - Na
- Silicon – Si Beryllium – Be
- Chromium – Cr Titanium - Ti

30. Valence Electrons and Bonding
Valence electrons are those electrons that have the highest energy level and are held most loosely.
All elements are most stable when there are 8 electrons in their valence shell
The number of valence electrons in an atom determines which elements it can bond with.

31. Isotopes
Atoms of the same element have the same number of protons but have different numbers of neutrons
Example of isotopes:
Hydrogen: