a. Sodium and chlorine are both third-period elements. Draw Lewis diagrams for each of these elements. b. What number of electrons would chlorine have to gain in order to achieve a "noble gas configuration"? What would be the charge on chlorine? c. What number of electrons would Na have to lose to obtain the noble gas configuration of Ne with eight valence electrons? What charge would Na have?

Valence electrons are the outermost electrons of an atom and play a pivotal role in chemical bonding and reactivity. For instance, in the exercise with sodium (Na) and chlorine (Cl), understanding that Na has 1 valence electron while Cl has 7 is fundamental.

These electrons reside in the outermost shell of an atom and determine how an element interacts with others to form compounds. The number of valence electrons is directly related to an element's position in the periodic table. Elements in the same group (column) typically have the same number of valence electrons, which explains their similar chemical properties.

For chemical bonding, atoms strive to achieve stability through the octet rule—having eight valence electrons, akin to the noble gas nearest to them in the periodic table. Consequently, elements will either lose, gain or share valence electrons to reach this stable configuration, leading to the formation of ions or covalent bonds in the process.

Noble gases are the inert, non-reactive elements found in Group 18 of the periodic table, ending with a full valence shell. Their stable configuration—typically eight valence electrons, except for helium which has two—is known as a 'noble gas configuration'.

Other elements undergo chemical changes to attain this desired state of stability. For instance, chlorine, as explained in the exercise, aspires to add one more electron to its seven valence electrons to emulate argon's configuration. Conversely, sodium, which has one valence electron, tends to lose that electron aiming to match neon's configuration.

When elements manage to achieve a noble gas configuration, they become more stable as ions. Chlorine becomes a chloride ion with a negative charge (Cl-), and sodium becomes a sodium ion with a positive charge (Na+). This principle explains much of the reactivity patterns observed across different elements on the periodic table.

The periodic table is a comprehensive chart that categorizes elements based on their atomic structure and properties. Its organization assists in predicting how elements will behave in chemical reactions. Key properties include atomic number, electron arrangements, and recurring chemical characteristics.

Each row, or period, indicates the number of electron shells, while each column, or group, shares common valence electron counts. For example, all Group 1 elements possess one valence electron and often display similar reactivity. Additionally, as you move from left to right across a period, the number of valence electrons increases.

The position of an element on the periodic table dictates its reactivity. Elements on the extreme left tend to be metals that readily lose electrons, turning them into cations, while those on the right, (apart from the noble gases), are more likely to gain electrons, forming anions. This understanding is essential, as it influences how we depict these elements using Lewis diagrams and predict their behavior in chemical bonding.