Problem 2 - Chemistry and Chemical Reactivity

Question

Give the periodic group number and number of valence electrons for each of the following atoms. (a) \(\mathrm{C}\) (d) Si (b) \(\mathrm{Cl}\) (e) Se (c) \(\mathrm{Ne}\) (f) \(\mathrm{Al}\)

Step-by-Step Solution

Answer

C: Group 14, 4 valence electrons; Cl: Group 17, 7 valence electrons; Ne: Group 18, 8 valence electrons; Si: Group 14, 4 valence electrons; Se: Group 16, 6 valence electrons; Al: Group 13, 3 valence electrons.

Step 1: Determine the Position in Periodic Table for Carbon (C)

Carbon (C) is located in Group 14 of the periodic table. To find it, note it is in the second period and occupies place 4 in the p-block, right above silicon (Si).

Step 2: Identify Valence Electrons for Carbon (C)

Elements in Group 14 have 4 valence electrons. Thus, carbon has 4 valence electrons.

Step 3: Determine the Position for Chlorine (Cl)

Chlorine (Cl) is located in Group 17 in the periodic table. It is found in period 3 within the p-block.

Step 4: Identify Valence Electrons for Chlorine (Cl)

Group 17 elements have 7 valence electrons. Therefore, chlorine has 7 valence electrons.

Step 5: Determine the Position for Neon (Ne)

Neon (Ne) is located in Group 18 of the periodic table, positioned within the p-block as well and in period 2.

Step 6: Identify Valence Electrons for Neon (Ne)

Being in Group 18, neon has 8 valence electrons, which makes it a noble gas with a full outer shell.

Step 7: Determine the Position for Silicon (Si)

Silicon (Si) is located in Group 14 of the periodic table, occupying the third period in the p-block, directly beneath carbon.

Step 8: Identify Valence Electrons for Silicon (Si)

As another member of Group 14, silicon also has 4 valence electrons.

Step 9: Determine the Position for Selenium (Se)

Selenium (Se) is situated in Group 16 and is part of period 4 in the p-block of the periodic table.

Step 10: Identify Valence Electrons for Selenium (Se)

Group 16 elements possess 6 valence electrons, thus selenium has 6.

Step 11: Determine the Position for Aluminium (Al)

Aluminium (Al) appears in Group 13 on the periodic table and is part of period 3 in the p-block.

Step 12: Identify Valence Electrons for Aluminium (Al)

Group 13 elements, including aluminum, have 3 valence electrons.

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding and reactivity. These electrons determine how atoms will interact with each other. Understanding valence electrons can help predict how elements will bond and form compounds. The number of valence electrons can be inferred from an element's position on the periodic table.

• Elements in Group 1 (Alkali Metals) have 1 valence electron.
• Elements in Group 2 (Alkaline Earth Metals) have 2 valence electrons.
• Groups 13 to 18 vary from 3 to 8 valence electrons.

For example, carbon (C), situated in Group 14, has 4 valence electrons, allowing it to form up to four covalent bonds with other atoms. This is why carbon is central to organic chemistry. Conversely, elements like neon (Ne) in Group 18 have a full outer shell with 8 valence electrons, making them typically unreactive.

Element Groups

Elements on the periodic table are organized into vertical columns known as groups. These groups contain elements with similar properties and valence electron configurations.

• Group 1: Alkali Metals
  These elements are highly reactive, especially with water, and have 1 valence electron.
• Group 14: Carbon Group
  Contains carbon, silicon, and other elements with 4 valence electrons, known for their ability to form multiple bonds.
• Group 17: Halogens
  Each element in this group has 7 valence electrons. Elements like chlorine (Cl) are reactive, often forming salts.
• Group 18: Noble Gases
  Inert due to having a full valence shell, typically 8 electrons, except for helium, which has 2.

The group number can often predict the number of valence electrons an element possesses, which helps in understanding the characteristics and chemical behavior of the element.

Periodic Trends

Periodic trends are predictable patterns seen across the periodic table related to the elements' structure and properties. These trends help explain why elements react a certain way and are critical for understanding chemistry.

• Atomic Radius: Generally increases down a group and decreases across a period from left to right.
  This is due to the addition of electron shells as you move down a group and the increased nuclear charge when moving across a period.
• Electronegativity: Tends to increase across a period and decrease down a group.
  Elements like fluorine (F) are highly electronegative, meaning they strongly attract electrons in a bond.
• Ionization Energy: Usually increases as you move across a period and decreases down a group.
  This trend signifies the energy required to remove an electron from an atom decreases with larger atomic size.

These trends help chemists predict how different elements will interact, making them essential for studying and understanding chemical reactions and compounds.