Bellwork

Write the electron configurations for magnesium and chlorine.

How many electrons do these elements have in their highest energy level?

Valence electrons are the electrons in the highest occupied energy level of an atom.

The number of valence electrons largely determines the chemical properties of an element.

The group number tells you the number of valence electrons.

Group 6A = Group 16 = 6 valence electrons

Valence Electrons

Applications of Group 4A Elements

Carbon Silicon Germanium

Lewis Dot Diagrams

• Because valence electrons are so important to the behavior of an atom, it is useful to represent them with symbols.

A Lewis dot diagram illustrates valence electrons as dots (or other small symbols) around the chemical symbol of an element.

• Each dot represents one valence electron.

• The element’s symbol represents the core of the atom—the nucleus plus all the inner electrons.

Lewis Dot Structures for Atoms

See supercool handout

 Classwork- Draw dot structures for the following elements and write which energy level the valence electrons are found in.

1. Hydrogen 2. Helium 3. Sodium 4. Magnesium 5. Aluminum 6. Silicon 7. Phosphorous 8. Oxygen 9. Flourine 10. Sulfur 11. Chlorine 12. Krypton 13. Iodine 14. Arsenic 15. Calcium 16. Tin 17. Xenon

Noble gases, such as neon and argon, are unreactive in chemical reactions. In 1916, chemist Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules.

The octet rule: In forming compounds, atoms tend to achieve the electron configuration of a noble gas.

Metals lose their valence electrons, leaving a complete octet in the next-lowest energy level.

Non-metals gain electrons to achieve a complete octet.

Metals produce cations when they lose electrons.

You can represent the electron loss, or ionization, of the sodium atom by drawing the complete electron configuration of the atom and of the ion formed.

Formation of Cations

The electron configuration of the sodium ion is the same as that of a neon atom.

Using electron dot structures, you can show the ionization more simply.

To draw a Lewis Dot Structure for an ion

1. Draw the structure for the neutral atom.

2. Add or subtract electrons depending on the ions charge. add an electron for each negative charge

subtract an electron for each positive charge

Example for Cl-

3. Place your structure in [brackets] and label the charge.

 Classwork- Draw dot structures for the following ions  18. H- 19. H+ 20. Na+ 21. Be2+ 22. Al3+ 23. Li+ 24. Ca2+ 25. O2-   26. F- 10. S2- 27. Cl- 28. I-

29. As3-   30. Why don’t noble gases form ions?

A magnesium atom attains the electron configuration of neon by losing both valence electrons. The loss of valence electrons produces a magnesium cation with a charge of 2+.

Walnuts are a good dietary source of magnesium. Magnesium ions (Mg2+) aid in digestive processes.

Cations of Group 1A elements always have a charge of 1+.

Cations of group 2A elements always have a charge of 2+.

The gain of negatively charged electrons by a neutral nonmetal produces an anion.

•The name of an anion typically ends in -ide.

The figure shows the symbols of anions formed by some elements in Groups 5A, 6A, and 7A.

A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion. It has the same electron configuration as the noble gas argon.

Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels.

In this equation, each dot in the electron dot structure represents an electron in the valence shell in the electron configuration diagram.

The negatively charged ions in seawater—the anions—are mostly chloride ions.

The ions that are produced when atoms of chlorine and other halogens gain electrons are called halide ions.

•All halogen atoms have seven valence electrons.

•Halogen atoms gain one electron to achieve the electron configuration of a noble gas (a stable full octet). Ex. Cl-

Oxygen is in Group 6A.

Conceptual Problem 7.1

7.1 Section Quiz.

1. How many valence electrons are there in an atom of oxygen?

a. 2

b. 4

c. 6

d. 8

7.1 Section Quiz.

2. Atoms that tend to gain a noble gas configuration by losing valence electrons are

a. metals.

b. nonmetals.

c. noble gases.

d. representative elements.

3. When a magnesium atom forms a cation, it does so by

a. losing two electrons.

b. gaining two electrons.

c. losing one electron.

d. gaining one electron.

7.1 Section Quiz.

4. When a bromine atom forms an anion, it does so by

a. losing two electrons.

b. gaining two electrons.

c. losing one electron.

d. gaining one electron

7.1 Section Quiz.