Question

Draw Lewis symbols showing the valence electrons of the following atoms. (a) \(\mathrm{Br}\) (c) \(S\) (e) \(\mathrm{Be}\) (b) \(\mathrm{Pb}\) (d) \(\mathrm{Ca}\) (f) \(\mathrm{Xe}\)

Short answer

The Lewis symbols for each atom are: \(Br\): \[\dot Br\], \(S\): \[\dot S\], \(Be\): \[\dot Be\], \(Pb\): \[\dot Pb\], \(Ca\): \[\dot Ca\], \(Xe\): \[\dot Xe\]. Each dot represents a valence electron for the atom.

Step-by-step solution

Identify the Valence Electrons of Each Atom

The first step is to identify the number of valence electrons for each atom. This can be done by looking up each atom on the periodic table or chemical reference material to identify which group (vertical column) it belongs to. For example, \(Br)\ belongs to group 7, so it has seven valence electrons.

Draw Lewis symbols

Next, draw the Lewis symbols for each atom. Start by writing the atomic symbol, then drawing the valence electrons as dots around the symbol. Remember to arrange the dots in pairs, with no more than two to a side. A maximum of eight electrons (four pairs) can be placed around a single symbol. For example for \(Br), write \(Br\) in the center and place seven dots around it.

Repeat for All Atoms

Repeat this process for each atom. For example, \(S)\ has six valence electrons, \(Be)\ has two, \(Pb)\ has four, \(Ca)\ has two, and \(Xe)\ has eight.

Key concepts

Valence Electrons

Valence electrons are the electrons found in the outermost shell of an atom. They are crucial because they determine how an element will react with others and form bonds. To find the number of valence electrons, you typically look at the group number the element is in on the periodic table. For instance, an element in group 7 will have seven valence electrons. This is because elements in the same group have similar outer electron configurations, which ultimately influence their chemical behavior. Understanding valence electrons is essential for constructing Lewis structures, which visually represent these electrons.

Periodic Table Groups

The periodic table is organized into vertical columns known as groups. Each group contains elements with the same number of valence electrons, which is why they often exhibit similar chemical properties. For example, elements in Group 1, such as \(\mathrm{Li}\), \(\mathrm{Na}\), and \(\mathrm{K}\), all have one valence electron. This organization helps chemists predict the types of bonds an element can form. Being familiar with periodic table groups allows you to quickly determine the number of valence electrons and thus draw accurate Lewis structures for each element.

Electron Pairing Scheme

In Lewis structures, valence electrons are depicted as dots surrounding the chemical symbols of elements. Electrons are first placed singly around the symbol, and only when necessary do they pair up. This is known as the electron pairing scheme. For instance, if an element has six valence electrons, you first place a single electron on each side of the symbol before pairing any up. This approach reflects the actual behavior of electrons which prefer to occupy empty orbitals before pairing. In the case of drawing a Lewis structure for an atom with three electrons, like aluminum (\(\mathrm{Al}\)), you would show one electron on each of three sides of the symbol before any pairing happens.

Chemical Symbols

Chemical symbols are abbreviations used to denote elements and allow for easy identification in chemical equations and formulas. Each element's chemical symbol can be found on the periodic table and typically consists of one or two letters, with the first being capitalized. For instance, \(\mathrm{Br}\) stands for bromine, \(\mathrm{S}\) for sulfur, and \(\mathrm{Xe}\) for xenon. Using these symbols becomes particularly handy when drawing Lewis structures, where each symbol acts as the center surrounded by valence electrons dotted around it. This shorthand representation simplifies complex chemical information, making it accessible and easier to work with.