1. Atoms, Elements & Molecules
The Building Blocks of the
Physical Universe.

2. Atoms Atoms are the absolute smallest units that make up matter.
Atoms are so small that we cannot see them with our bare eyes, they are so small that we can’t even see them with a light microscope.
An element is a substance made from only one type of atom.
Two or more atoms combined together makes a molecule.

3. Protons, Neutrons and Electrons
An atom has three parts:
Proton = positive
Neutron = neutral, meaning they have no charge
Electron = negative
The proton & neutron are found in the center of the atom, a place called the nucleus.
The electrons orbit the nucleus.

4. What Does an Atom Look Like?

5. Graphic from http://education.jlab.org/atomtour/fact2.html
The Atom Continued -
Graphic from

6. Elements
Over time, scientist began to realize that every different atom makes a different element. For example atoms of a certain kind make up carbon and atoms of another kind make up hydrogen.
The number of protons in an atom determines what element it will be.
A long time ago people learned that it is impossible to turn one kind of atom into another.

7. What are elements?
Elements are made of atoms. While atoms may have different masses and the number of parts, they are all built in the same way.
Elements are necessary if you want to make molecules.
Elements are to molecules as the alphabet is to words.

8. Report on Development of the Atom
Work together with classmates at your table.
Obtain:
Grade 7 Textbook ( )
OER Textbook (17-22)
Select a scientist
Write a short report on your scientist, using the textbooks as your sources. Use a separate piece of paper and include the names of your group.
Choose one of the following scientists:
Democritus
Dalton
Thomson
Rutherford
Bohr

9. History Early Greek Theories
Because atoms are so incredibly small, scientists have had to make new tools and technology to be able to study them. This has led to generations of scientists discovering more and more about atoms.
• 430 B.C. - Democritus thought matter could not be divided indefinitely. He called these indivisible pieces atomos.
• 350 B.C - Aristotle rejected this idea and modified an earlier theory that matter was made of four “elements”: earth, fire, water, air.
• Aristotle was wrong. However, his theory persisted for 2000 years.

10. John Dalton
It wasn’t until the 1800s that the next scientist John Dalton brought back the idea of an atom. However, rather than just make theories about the idea he did experiments to try to learn more.
He said that all matter is made of atoms and atoms of a single element are identical and that different atoms combine to make molecules.

11. Dalton (con’t)
Dalton was the first scientist to create a model of the atom. Models are used to represent what scientists think atoms look like, or how they move. However, models don’t always perfectly show all the parts of what it is they represent.
“Billiard Ball” Model

12. Atoms cannot be subdivided, created, or destroyed.
Billiard Ball Model
Atoms cannot be subdivided, created, or destroyed.

13. History - Thomson Joseph J. Thomson
In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles.
Thus he is credited with the discovery and identification of the electron; and with the discovery of the first subatomic particle.
Plum Pudding Model
Joseph J. Thomson

14. Plum Pudding Model (1897)

15. History - Rutherford Ernest Rutherford
Geiger–Marsden experiment, which demonstrated the nuclear nature of atoms by deflecting alpha particles passing through thin gold foil.
A very small positive charged nucleus, containing most of the atom's mass, was orbited by low-mass electrons.
Planetary Model (1911)
Ernest Rutherford

16. Positive charged nucleus with orbiting electrons.
Planetary Model (1911)
Positive charged nucleus with orbiting electrons.

17. History - Bohr Niels Bohr
A negatively charged electron, confined to an atomic orbital, orbits a small, positively charged nucleus.
He introduced the idea that an electron could drop from a higher-energy orbit to a lower one, thus emitting a quantum of energy.
Bohr Model
Niels Bohr

18. Bohr Model (1913)
Depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus.

19. Electron Cloud Model
Today we use the Electron Cloud Model. It looks a lot like Bohr’s model, the protons and neutrons stay in the nucleus and the electrons are in different levels around the nucleus.
The Electron Cloud model says that the electrons move around randomly and don’t always stay in the same place. Electrons move like waves but stay in the same orbital.

20. Progression of the Atomic Model Democritus & John Dalton+ -
The structure of an atom, according to:
Democritus & John Dalton
James Chadwick
Neils Bohr
J.J. Thomson
Ernest Rutherford
Erwin Schrodinger

21. Periodic Table of Elements
To better organize the elements, or different types of atoms, Dimitri Mendeleev created a periodic table of elements (1869)

22. … Elements ... Elements build all matter in the universe.
All the elements of matter make up the Periodic Table. You could call it the alphabet of chemistry.
The Periodic Table provides several items of information, like …

23. Periodic Table of Elements - Continued
The number above each element symbol or letter is its atomic number. The atomic number = the number of protons in the nucleus. Example: Hydrogen 1 Oxygen 8 Carbon Nitrogen 7 Iron 26
The number below each element symbol or letter is its atomic mass. The atomic mass = number of protons plus neutrons in its nucleus.
The number of electrons is usually equal to the number of protons in an atom.

25. Electrons have special rules …
You can’t just shove all of the electrons into the first orbit of an electron.
Electrons live in something called shells or energy levels.
Only so many can be in any certain shell.

26. Electron Shell Configuration
Electrons live in something called shells or energy levels.
Only a certain number of electrons can be in any certain shell.
The electrons in the outer most shell of any element are called valance electrons.
Nucleus
1st shell
2nd shell
3rd shell
Adapted from

27. And now let’s try ... ___ How to draw a Lithium atom:
First – Examine the Periodic Table
Second – Determine the number of protons (Atomic Number)
Third – Determine the number of neutrons (Atomic Mass – Atomic Number)
Fourth – Determine the number of electrons (Refer to Atomic Number) __
___
______

28. Current Atomic Model - + + -
The current atomic (Bohr) model shows all of the particles in the atom.
In the center are circles. Each circle represents a single neutron or proton. Protons should have a plus (+) or P written on them. Neutrons should be blank or have an N.
In a circle around the nucleus are the electrons. Electrons should have a minus sign (-) or an e. - + + -

29. 2 in the 1st shell, 1 in the 2nd shell
Draw a Model:
Protons = 3 3 Li
Lithium 7
Neutrons = 4
(7-3=4)
Electrons = 3
2 in the 1st shell, 1 in the 2nd shell