Question

section 2 review
sc.912.p
key ideas

1. explain why elements in a group on the periodic table have similar chemical properties.
2. compare the number of valence electrons in an atom of oxygen, o, with the number of valence electrons in an atom of selenium, se. are oxygen and selenium in the same period or group?
3. explain why some atoms gain or lose electrons to form ions.
4. describe why lithium and other group 1 elements usually form positive ions, while fluorine and other group 17 elements form negative ions.
5. list the three main categories of elements, and give an example of each.

Explanation:

Step1: Explain periodic - table group similarity

Elements in a group have same number of valence electrons. Valence electrons determine chemical behavior, so they have similar chemical properties.

Step2: Compare oxygen and selenium

Oxygen has 6 valence electrons. Selenium also has 6 valence electrons. They are in the same group (Group 16) as they have the same number of valence electrons.

Step3: Explain ion - formation

Atoms gain or lose electrons to achieve a stable electron configuration like noble gases. A stable configuration usually has a full outer shell.

Step4: Explain Group 1 and 17 ion - formation

Group 1 elements have 1 valence electron. They lose this electron to have a full outer shell and form positive ions. Group 17 elements have 7 valence electrons. They gain 1 electron to have a full outer shell and form negative ions.

Step5: List element categories

The three main categories are metals (e.g., iron), non - metals (e.g., oxygen), and metalloids (e.g., silicon).

Answer:

1. Elements in a group have similar chemical properties because they have the same number of valence electrons which determine chemical behavior.
2. Oxygen and selenium both have 6 valence electrons and are in the same group (Group 16).
3. Atoms gain or lose electrons to achieve a stable electron configuration like noble gases.
4. Group 1 elements have 1 valence electron and lose it to form positive ions; Group 17 elements have 7 valence electrons and gain 1 to form negative ions.
5. The three main categories of elements are metals (e.g., iron), non - metals (e.g., oxygen), and metalloids (e.g., silicon).