1. Core and Valence Electrons
Why do elements in the same group have similar properties?

2. Alchemy Unit – Investigation III
Lesson 4:
Life on the Edge
EQ: Why do elements in the
same group have similar
properties?

3. a. Where are these elements located on the periodic table?
Warm-Up:
The three atoms below have similar reactivity and chemical behavior.
a. Where are these elements located on the periodic table?
b. What do you think is
responsible for their
similar properties?
Unit 1 • Investigation III

4. Activity Fill in the missing atoms on the chart.
1. What do all of the atoms in Group I have in common?
2. How does the number of electrons change as you move from atom to atom across a row?
3. How does the arrangement of the electrons change as you move down the columns?
Unit 1 • Investigation III

5. Copy the following definitions:
4. How many shells of electrons does bromine have? How many electrons are in bromine’s outermost shell?
5. Predict the number of electrons in iodine’s outermost shell. Explain your thinking.
6. What happens to the electron count and the number of shells when you move from neon (Ne) to sodium (Na)?
Copy the following definitions:
Valence Electrons: electrons on the outermost shell.
Core Electrons: electrons on the inner shell(s)‏
Unit 1 • Investigation III

6. 7. How many valence electrons are found in:
a. Se
b. Na
c. the halogens
d. the noble gases
group 3
8. How many core electrons are found in:
a. Oxygen
b. Ne
c. K
d. Ge
e. Br
Unit 1 • Investigation III

7. How many shells will Rb have? How many
9. If an atom has four shells containing electrons, what row (period) is it in?
How many shells will Rb have? How many
electrons will be in the valence shell?
11. Explain how you can determine the arrangement of an element’s electrons, from the element’s position on the periodic table.
Unit 1 • Investigation III

8. Notes
Bohr proposed that electrons could be found in different shells around the nucleus.
The letter “n” is referred to as the quantum number.
Unit 1 • Investigation III

9. (cont.)‏
(cont.)‏
Unit 1 • Investigation III

10. The outermost shell of each drawing is called the valence shell.
(cont.)‏
The outermost shell of each drawing is called the valence shell.
The valence shell contains the valence electrons.
All other electrons are considered core electrons.
Unit 1 • Investigation III

11. Wrap-Up
Electrons occupy different shells around the nucleus of an atom.
Each electron shell can hold a specific maximum number of electrons.
The valence electrons are in the outermost electron shell of an atom. Electrons that are not valence electrons are called core electrons.
Elements with the same number of valence electrons have similar chemistry and are in the same group.
Unit 1 • Investigation III

12. Ticket Out: Provide the following information for element #34.
a) element’s name and symbol.
b) number of protons in the nucleus.
c) total number of electrons for this element.
d) number of core electrons for this element.
e) number of valence electrons.
f) group number for this element.
g) names of other elements with similar properties.
Unit 1 • Investigation III