Question

Write Lewis symbols for the following atoms: (a) \(\mathrm{K}\) (b) Ge, (c) As, (d) \(\mathrm{Br}\) (e) Se.

Short answer

Lewis symbols for (a) K: K•, (b) Ge: Ge with four dots around it, (c) As: As with five dots around it, (d) Br: Br with seven dots around it, (e) Se: Se with six dots around it.

Step-by-step solution

Understanding Lewis Symbols

Lewis symbols represent the valence electrons of an atom as dots around the element's chemical symbol. Valence electrons are the electrons in the outermost shell that can participate in chemical bonding. Group number of the element in the periodic table usually gives the number of valence electrons, except for the transition metals, which can be more complex.

Determining Valence Electrons for Potassium (K)

Potassium (K) belongs to Group 1 of the periodic table and thus has 1 valence electron. Its Lewis symbol is K with one dot around it.

Determining Valence Electrons for Germanium (Ge)

Germanium (Ge) sits in Group 14 of the periodic table which means it has 4 valence electrons. Its Lewis symbol is Ge with four dots around it, placed separately on the four sides of the symbol.

Determining Valence Electrons for Arsenic (As)

Arsenic (As) is in Group 15 of the periodic table and has 5 valence electrons. Its Lewis symbol is As with five dots around it, with one pair of dots on one side and the rest unpaired.

Determining Valence Electrons for Bromine (Br)

Bromine (Br) is a member of Group 17 in the periodic table and therefore has 7 valence electrons. Its Lewis symbol is Br with seven dots, with three pairs of dots and one unpaired dot.

Determining Valence Electrons for Selenium (Se)

Selenium (Se) is part of Group 16 which implies it has 6 valence electrons. Its Lewis symbol is Se with six dots, with three pairs of dots.

Key concepts

Valence Electrons

Valence electrons play a pivotal role in understanding chemical behavior, as they are the electrons responsible for forming bonds between atoms. These electrons are found in the outermost shell of an atom and can be identified using periodic table groups. For example, atoms in Group 1 of the periodic table, such as potassium (K), possess one valence electron; whereas, germanium (Ge) in Group 14 will have four valence electrons due to its position. Understanding valence electrons is crucial, as it helps you draw Lewis symbols, which are simple notations representing the valence electrons as dots around the atomic symbol.

This concept is vital for making predictions about the types of bonds that an atom may form and its reactivity. For instance, elements in Group 17 like bromine (Br) have seven valence electrons, making them one electron short of a complete shell, which drives them to readily accept electrons from other atoms during bonding.

Chemical Bonding

Chemical bonding is the physical process responsible for the attractive interactions between atoms and molecules. There are several types of bonds that can form, such as ionic, covalent, and metallic bonds. The type of bond that forms is largely determined by the elements involved and their valence electrons. For instance, elements with just one valence electron, such as potassium (K), often form ionic bonds by donating their electron to achieve a full outer shell. Similarly, atoms like arsenic (As) and selenium (Se), may share electrons to complete their valence shell, resulting in covalent bonds.

Understanding Lewis symbols, which depict the distribution of valence electrons around the atomic symbol, allows us to predict and illustrate the bonding tendencies of different elements. Molecules stabilize through chemical bonds because achieving a full valence shell lowers the potential energy of the system, guiding the formation of compounds.

Periodic Table Groups

The periodic table is divided into groups (vertical columns) and periods (horizontal rows) that arrange elements by increasing atomic number and similar chemical properties. Groups are particularly relevant when discussing valence electrons, as they can often tell you the number of these electrons an atom has. For example, germanium (Ge) is in Group 14, thus it has four valence electrons, contributing to its chemical characteristics.

As you move from left to right across a period, the number of valence electrons in atoms generally increases. This sequence helps in predicting how atoms will react chemically. Atoms within the same group, such as arsenic (As) and selenium (Se) from Group 15 and 16 respectively, exhibit similar valence electron configurations, resulting in predictable similarities in their chemical behavior. Knowing how to interpret the periodic table and its groups is thus an essential skill in the study of chemistry.