1. Section 2: Exploring the Periodic Table
Preview
Key Ideas
Bellringer
The Role of Electrons
Ion Formation
How Are Elements Classified?

2. Key Ideas
Why do elements within a group of the periodic table have similar chemical properties?
What happens to an atom that gains or loses electrons?
What are the three main categories of elements?

3. Bellringer
Each square on the periodic table of elements includes an element’s name, chemical symbol, atomic number, and atomic mass. Below are examples of elements found on the periodic table.

4. Bellringer, continued
Which element above has the highest atomic number?
Which element above has the lowest atomic mass?
What is the chemical symbol for calcium?
What is the element name for Cr?

5. The Role of Electrons
Why do elements within a group of the periodic table have similar chemical properties?
The periodic trends in the periodic table are the result of electron arrangement.

6. The Role of Electrons, continued
Valence electrons account for similar properties.
An element’s location in the periodic table is related to electron arrangement.
Example: Lithium and sodium, in Group 1, each have one valence electron.

7. Visual Concept: Valence Electrons

8. Ion Formation What happens to an atom that gains or loses electrons?
If an atom gains or loses electrons, it no longer has an equal number of electrons and protons. Because the charges do not cancel completely, the atom has a net electric charge.

9. Ion Formation, continued
Group 1 elements form positive ions.
The single valence electron is easily removed.
Group 17 elements form negative ions.
The addition of one valence electron fills the outer energy level.

10. How Are Elements Classified?
What are the three main categories of elements?
All elements are either metals, nonmetals, or semiconductors.

11. How Are Elements Classified?, continued
Elements in each category have similar properties.
metal: an element that is shiny and that conducts heat and electricity well
nonmetal: an element that conducts heat and electricity poorly
semiconductor (or metalloid): an element or compound that conducts electric current better than an insulator does but not as well as a conductor does

12. Visual Concept: Comparing Metals, Nonmetals, and Metalloids

13. How Are Elements Classified?, continued