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The Periodic Table
Section 2
Section 2: Exploring the Periodic Table
Preview
• Key Ideas
• Bellringer
• The Role of Electrons
• Ion Formation
• How Are Elements Classified?
The Periodic Table
Section 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?
The Periodic Table
Section 2
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.
The Periodic Table
Section 2
Bellringer, continued
1. Which element above has the highest atomic number?
2. Which element above has the lowest atomic mass?
3. What is the chemical symbol for calcium?
4. What is the element name for Cr?
The Periodic Table
Section 2
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.
The Periodic Table
Section 2
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.
The Periodic Table
Section 2
Visual Concept: Valence Electrons
The Periodic Table
Section 2
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.
The Periodic Table
Section 2
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.
The Periodic Table
Section 2
How Are Elements Classified?
〉What are the three main categories of
elements?
〉All elements are either metals, nonmetals, or
semiconductors.
The Periodic Table
Section 2
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
The Periodic Table
Section 2
Visual Concept: Comparing Metals,
Nonmetals, and Metalloids
The Periodic Table
Section 2
How Are Elements Classified?, continued