1. Aim: Where do we find electrons in an atom?
Do Now:
Take out a reference table and a calculator.
Calculate the number of neutrons an atom of the following elements will have.
Cl 37
U 235
I 127

2. Answer to the Do Now:

3. How can we tell the number of electrons in an atom?
In an electrically neutral atom (an atom that does not have a charge), the atom will have the same number of protons and electrons.
Example: How many protons does an atom of He have? _________. Therefore, the same atom will have _________ electrons.
How many electrons does an atom of Cl have?
How many electrons does an atom of Au have?

4. What about atoms that are NOT electrically neutral?
It depends on whether the atom has a positive or negative charge. Atoms with charges are called ions.
If an atom has a positive charge, it has more protons than neutrons.
If an atom has a negative charge, it has more electrons than protons.

5. How do we write a symbol if the atom is an ion?
The actual symbol remains the same.
If the atom is charged, write the symbol and the charge on the upper right of the symbol.
Example: Mg2+ has a positive charge. How many protons and electrons does it have?
Example: Cl- has a negative charge. How many protons and electrons does it have?

6. Where do we find electrons in an atom?
Remember – Electrons are found outside the nucleus in orbitals.
Orbitals form a series of energy levels in which electrons may be found.
Each electron has its own distinct amount of energy that corresponds to the energy level it occupies.
The electron configuration for an element can be found in the periodic table of elements.

7. What is the electron configuration for…
Magnesium?
Hafnium?
Copper?
What does that mean?

8. Drawing Electron Configurations
What do you notice about the number of electrons in each level?

9. Activity/Homework #