Question

Give the number of valence electrons and draw electron-dot symbols for atoms of the following elements: (a) \(\mathrm{Kr}\) (b) C (c) Ca (d) \(\mathrm{K}\) (e) \(\mathrm{B}\) (f) \(\mathrm{Cl}\)

Short answer

(a) Kr: 8 valence electrons; (b) C: 4; (c) Ca: 2; (d) K: 1; (e) B: 3; (f) Cl: 7.

Step-by-step solution

Determine the Valence Electrons for Kr

Krypton (Kr) is a noble gas and it is located in group 18 of the periodic table. The elements in this group have a full outer shell of electrons. For Kr, it has 8 valence electrons in its outermost shell, which is typical for noble gases.

Draw Electron-Dot Symbol for Kr

The electron-dot symbol for Kr is represented by the symbol of Kr with 8 dots around it, representing its 8 valence electrons. These dots are evenly spaced around the symbol. \[ ext{Kr:} igcdot igcdot igcdot igcdot igcdot igcdot igcdot igcdot \]

Determine the Valence Electrons for C

Carbon (C) is located in group 14 of the periodic table, which means it has 4 valence electrons.

Draw Electron-Dot Symbol for C

The electron-dot symbol for C is represented by the symbol of C surrounded by 4 dots, which correspond to its 4 valence electrons.\[ ext{C:} igcdot igcdot igcdot igcdot \]

Determine the Valence Electrons for Ca

Calcium (Ca) is located in group 2, indicating it has 2 valence electrons.

Draw Electron-Dot Symbol for Ca

The electron-dot symbol for Ca is depicted as the symbol of Ca with 2 dots around it, representing its valence electrons.\[ ext{Ca:} igcdot igcdot \]

Determine the Valence Electrons for K

Potassium (K) is in group 1 of the periodic table, which means it has 1 valence electron.

Draw Electron-Dot Symbol for K

The electron-dot symbol for K is shown by the symbol of K with 1 dot around it, reflecting its single valence electron.\[ ext{K:} igcdot \]

Determine the Valence Electrons for B

Boron (B) is found in group 13, thus it has 3 valence electrons.

Draw Electron-Dot Symbol for B

The electron-dot symbol for B is the symbol of B with 3 dots indicating its valence electrons.\[ ext{B:} igcdot igcdot igcdot \]

Determine the Valence Electrons for Cl

Chlorine (Cl) is a group 17 element and it contains 7 valence electrons.

Draw Electron-Dot Symbol for Cl

The electron-dot symbol for Cl is shown using the symbol of Cl surrounded by 7 dots, representing the valence electrons.\[ ext{Cl:} igcdot igcdot igcdot igcdot igcdot igcdot igcdot \]

Key concepts

Electron-Dot Symbols

Electron-dot symbols, also known as Lewis dot structures, are a visual representation that show the valence electrons around an atom. These diagrams are simple and intuitive, making them a great way to understand how atoms interact and bond with each other. To create an electron-dot symbol, you start by writing the elemental symbol. Then, surround it with dots that represent each valence electron.
This method helps quickly visualize how many electrons are available for forming bonds, which is crucial for understanding chemical reactions.

• Each dot represents one valence electron.
• Dots are placed around the element's symbol, typically up to eight.
• Dot placement can vary, but they are often spaced evenly to follow governance of symmetry.

When drawing electron-dot symbols, consider that elements in the same group of the periodic table will have similar symbols since they have the same number of valence electrons.

Periodic Table Groups

The periodic table is organized into columns known as groups or families. Each group contains elements that have similar chemical properties due to having the same number of valence electrons. This is a crucial factor in predicting how an element might behave in a chemical reaction.

• Group 1: Elements like potassium (K) have 1 valence electron.
• Group 2: Alkaline earth metals like calcium (Ca) possess 2 valence electrons.
• Group 14: Carbon (C) belongs here with 4 valence electrons.
• Group 13: Boron (B) has 3 valence electrons.
• Group 17: Halogens like chlorine (Cl) have 7 valence electrons.
• Group 18: Noble gases like krypton (Kr) have a complete outer shell with 8 valence electrons.

Understanding these groups helps to predict and explain the chemical behavior of elements like bonding and reactivity.

Noble Gases

Noble gases are a group in the periodic table, known as Group 18. They include elements like krypton (Kr), neon (Ne), and argon (Ar). These elements are characterized by having a full valence shell of electrons, which makes them exceptionally stable and inert.

• They have 8 valence electrons, except for helium, which has 2.
• The complete valence shell means they rarely participate in chemical reactions.
• They are often used in conditions requiring non-reactive environments, such as in light bulbs with argon or in signage using neon.

Their stability is why noble gases are often used to explain concepts in chemical bonding, as other elements often strive to achieve a similar electron configuration through bonding.

Valence Shell

The valence shell is the outermost shell of an atom, and it contains the valence electrons. These are the electrons involved in chemical bonding, and they play a key role in determining an element's chemical properties and reactivity.

• The valence shell can hold up to 8 electrons, according to the octet rule.
• Elements with a full valence shell are typically stable and less reactive.
• The desire to have a full valence shell drives atoms to bond with others, either by sharing electrons (covalent bonds) or transferring electrons (ionic bonds).

Understanding the valence shell and its electrons is fundamental to grasping how elements interact and form compounds, such as why sodium (with 1 valence electron) eagerly bonds with chlorine (with 7 valence electrons) to form table salt.