1. Chapter 9 Lesson 2
Elements and Atoms

2. Matter, elements, and atoms

3. What are elements?
Definition: pure substances that cannot be broken down any further into anything simpler.
Make up all of the matter in the world.
Can be solids, liquids, or gases.

4. The Periodic Table
There are 112 known elements, which are categorized into the periodic table.

5. Mixtures of Elements Sometimes, they are physically mixed together.
Example: oxygen and nitrogen in the air
Sometimes, they are chemically mixed together.
Example: salt is a chemical combination of sodium and chlorine.
Example: Sugar is a chemical combination of carbon, hydrogen, and oxygen.
Few elements are found in their pure form, and some are not found outside of a lab.

6. Atoms Atoms make up elements. How small do you think atoms are?

7. Atoms and Elements
Atoms in the same element have the same chemical properties as that element.
Example: the atoms in gold have a different structure than the atoms in oxygen.
Scientists study the elements to better understand the atoms they are made up of.

8. Famous Scientists Democritus John Dalton Greek philosopher
First to believe atoms existed
He said that matter must be made up of tiny particles.
John Dalton
In 1803 he presented a simple atomic theory.
He studied how gases could be mixed together.
Concluded that there are solid particles in gases that compress together when mixed.

9. The Parts of the Atom
An atom has three parts, neutrons, electrons, and protons.
Neutrons and protons are found inside the nucleus. Electrons orbit around the nucleus.

10. The Nucleus The densest part of the atom (has the most mass).
Located in the center of the atom; the rest of the atom is just empty space.
Contains the protons and the neutrons.
Protons have a positive electric charge.
Neutrons have no (or a neutral) electric charge.
The mass of the nucleus is measured in atomic mass.
The sum of the atom’s protons and neutrons.
The units for atomic mass are amu.

11. The Electrons Smaller than protons and neutrons.
Have a negative charge.
Move around the nucleus in a “cloud”.
Held near the nucleus by their electrical attraction to the protons.
The number of electrons equals the number of protons.
Therefore, if an atom has 12 protons, it has ________ electrons.
The atomic number is the number of protons OR electrons.

12. Day 2

13. How Have Ideas About Atoms Changed?
Over time, the idea of how the atom looks has changed. Your job for today is to chronicle the advancements in the discovery of the atom. Use the information on page E21 in your textbook to fill in the events from the Atom Theories page on your timeline.

14. Timeline of an Atom

15. Timeline of an Atom J.J. Thomson Had no particles inside
Electrons orbited the nucleus; electrons sprinkled throughout positive fluid (like raisins in pudding).
Contained electrons
Had no particles inside
John Dalton
Solid
Ernest Rutherford and H.G.J. Mosley
The positive matter was packed into a tiny nucleus
Isotopes – the same number of protons and a different number of neutrons.
Has a unique number of protons called an atomic number
Electrons thought of as “clouds” surrounding the nucleus

16. The Periodic Table of Elements
Using their understanding of the elements, scientists were able to create the Periodic Table of Elements.
Dmitry Mendeleev created the Periodic Table we use today.

17. Reading the Periodic Table
Atomic mass (weight) – the number of protons AND neutrons
Atomic number – the number of protons OR electrons