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

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?

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.

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?

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 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.

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.

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.

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

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

How Are Elements Classified?, continued