Atom Notes

1. Exploring Inner Space
TEKS 8.5A describe the structure of atoms including the masses, electrical charges and locations, of protons and neutrons in the nucleus and electrons in the electron cloud
TEKS 8.5B identify that protons determine an element’s identity and valence electrons determine its chemical properties, including reactivity

2. Each element on the Periodic Table is made of the same kind of atom.

3. Each atom in an element has the same number of protons.

4. The number of protons present in the atom is what determines the element’s identity and is shown by the atomic number.

5. Structure of the Atom

6. The Nucleus
The center of the atom is called the nucleus .
proton
neutron
nucleus
3
Li
6.941
Lithium

7. The nucleus contains protons and neutrons.

8. Since each proton and neutron in the nucleus has a mass of 1 atomic mass unit (amu), we can add the number of protons and neutrons together to find the atomic mass.

9. On your Periodic Table, fill in this information.
# protons = element’s identity = atomic number

10. # protons + # neutrons = atomic mass
On your Periodic Table, fill in this information.

11. The Periodic Table shows the mass for each element as a decimal.
We will usually round the atomic mass number.

12. 
If the mass number is known, and you know the number of protons, how can you find the number of neutrons?
Mass # - # Protons = # Neutrons

13. fill in this information on your Periodic Table
mass - # protons = # neutrons
# protons = # electrons in a stable atom

14. electron
energy levels
3
Li
6.941
Lithium
electron cloud
The Electron Cloud and Energy Levels

15. Surrounding the nucleus is an area called the electron cloud.
Inside the electron cloud, electrons orbit around in different energy levels.

16. The electrons are so small that they basically have no mass, so they are not included in finding the atomic mass.
electronneutronproton

17. first energy level
The first energy level, which is closest to the nucleus, holds up to 2 electrons.

18. second energy level
The second energy level holds up to 8 electrons.

19. third energy level
The third energy level may hold 8 or more electrons.
8 or more!

20. How many electrons are in each energy level of the element Lithium?
electron
energy levels
3
Li
6.941
Lithium
electron cloud
1st – 2, 2nd – 1

21. By numbering the periods (rows) on the Periodic Table, you can determine how many energy levels are in an atom.
For example, Lithium is in period 2, therefore it has 2 energy levels.
Number the first three periods on your Periodic Table.

23. How many energy levels does sodium contain?
Period 3, 3 energy levels

24. The most stable form of an atom is electrically neutral. This means that the number of protons and electrons is equal.
Atomic # = Protons = Electrons

25. Valence Electrons
The numbers of electrons in an atom’s outermost energy level are called valence electrons.

26. These electrons are important because they determine how reactive the element is with other elements.

27. Valence electrons…..
valence electrons are found here!

28. For example, look at the element oxygen. Oxygen is atomic number 8, which means it has 8 protons (+).

29. Therefore, in a stable oxygen atom, there are 8 electrons (-). The positive and negative charges are balanced.

30. 6
Look at your Periodic Table. Find the element Carbon.
How many positive (protons) charges does carbon have?

31. How many negative charges (electrons) does carbon have?
6

32. What is the mass of carbon? 12.0112 How can the number of neutrons be determined? (atomic mass - # protons = # neutrons) Carbon has 6 neutrons.