Question

Write the Lewis symbol for each atom or ion. a. \(A l\) b. \(\mathrm{Na}^{+}\) c. Cl d.\(\mathrm{Cl}^{-}\)

Short answer

Lewis symbols: a. Al has three dots, b. Na+ has no dots, c. Cl has seven dots arranged in three pairs and one single, d. Cl- has eight dots arranged in four pairs.

Step-by-step solution

- Understanding Lewis Symbols

Lewis symbols represent an atom or ion showing its valence electrons as dots around the symbol of the element. Each side (top, bottom, left, right) of the element symbol represents an orbital that can hold up to two electrons.

- Writing the Lewis Symbol for Aluminum (Al)

For Al, which is in group 13, it has three valence electrons. Place three dots around the symbol of Al: one dot on two sides and one lone dot on the third side, representing the three valence electrons.

- Writing the Lewis Symbol for Sodium Ion (Na+)

A sodium ion loses one electron to form a Na+ cation. Since Na is in group 1, it originally has one valence electron, which it loses. Therefore, the Lewis symbol for Na+ has no dots, representing the loss of its valence electron.

- Writing the Lewis Symbol for Chlorine (Cl)

Chlorine is in group 17 and has seven valence electrons. Place three pairs of dots on three sides of the element symbol, and one lone dot on the fourth side.

- Writing the Lewis Symbol for Chloride Ion (Cl-)

A chloride ion gains one electron to form a Cl- anion. Since Cl has seven valence electrons, the extra electron makes a total of eight. Place four pairs of dots around the Cl symbol, one on each side to represent the eight valence electrons.

Key concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom, which play a fundamental role in chemical reactions and bonding. These electrons determine how an element will react with others and are depicted in Lewis symbols as dots surrounding the element's symbol.

For instance, aluminum (Al) has three valence electrons since it belongs to group 13 of the periodic table. In visual terms, we illustrate these electrons as three distinct dots around the symbol 'Al'. The positioning of the dots implies the potential pairing of electrons which is crucial for bonding. It's like a social gathering where everyone has a 'dance card,' and the dots are the number of available dances they have to share.

During chemical reactions, atoms strive to reach a stable electronic configuration, often akin to the nearest noble gas. This ability to gain or lose electrons to achieve stability is why understanding the number and arrangement of valence electrons is so pivotal.

Electron Configuration

The electron configuration of an atom describes the distribution of its electrons among various orbitals. This arrangement is governed by certain principles, like the Pauli exclusion principle and Hund's rule, to ensure the most stable and energetically favorable structure.

Consider the example of sodium (Na) which is inherently in possession of one 'dance ticket' or valence electron. Sodium prefers to 'give away' this ticket, adopting a configuration akin to the preceding noble gas, neon. This results in the positively charged sodium ion (Na+), with no 'dance tickets' left to offer, shown by an empty set of dots in its Lewis symbol.

Electron configurations reveal not just the atom's reactive nature but also its magnetic properties and the types of chemical bonds it can form. It's reminiscent of giving someone a map to a treasure chest; the configuration is a guiding blueprint to an atom's most prized possessions - its electrons.

Ionic and Covalent Bonding

Ionic and covalent bonding represent the two primary ways atoms can 'dance' together to achieve full 'dance cards', or stable electron configurations.

In ionic bonding, atoms transfer electrons unequivocally, leading to the formation of ions with full 'dance cards'. A perfect example is the pairing of Na+ and Cl-. Sodium gives away its electron 'ticket', embracing a positive charge, while chlorine welcomes the extra electron 'ticket' with open arms, becoming negatively charged (Cl-). The opposites attract, creating a strong ionic bond, as shown by their respective Lewis symbols, devoid and full of dots.

On the flip side, covalent bonding is about sharing 'dance tickets.' Two chlorine (Cl) atoms each have one unpaired electron ‘ticket’. By uniting their unpaired 'tickets', they establish a shared pair, essentially dancing together and filling their 'dance cards' through mutual cooperation. This shared electron pair, represented by a pair of dots between the symbols for Cl in a Lewis structure, exemplifies the alliance of covalent bonding.