Question

An atom has atomic number 6 and has eight electrons. (a) Which element is this? (b) Is this a neutral atom, a cation, or an anion? If it is an ion, what is its charge? (c) Draw a Bohr diagram for this atom in its ground state.

Short answer

(a) The element is carbon (C). (b) It is an anion with a charge of -2. (c) The Bohr diagram shows the carbon anion with a nucleus of C and its charge -2, surrounded by two electron shells: the first shell has 2 electrons, and the second shell has 6 electrons.

Step-by-step solution

Identify the element

An atom's atomic number represents the number of protons in its nucleus. In this case, the atomic number is 6. To identify this element, we can compare the atomic number to the periodic table. The element with the atomic number 6 is carbon (C).

Determine whether it is a neutral atom, cation, or anion

A neutral atom has an equal number of protons and electrons. In this case, we have 6 protons and 8 electrons. Since the number of electrons is more than the number of protons, it's not a neutral atom. A cation is an atom that has lost one or more electrons, resulting in a positive charge. An anion is an atom that has gained one or more electrons, resulting in a negative charge. As our atom has gained two electrons (as it has 8 electrons instead of the 6 it would have as a neutral atom), it is an anion.

Calculate the charge of the ion

The charge of an ion is given by the difference between the number of protons and electrons. In this case, we have 6 protons and 8 electrons, so the charge of the ion is (\(6 - 8 = -2\)). This anion has a charge of -2.

Draw a Bohr diagram for this atom in its ground state

A Bohr diagram represents an atom with concentric circles representing electron shells and electrons placed on these shells according to their energy levels. In its ground state, electrons fill the lowest energy levels first. 1. Draw a circle in the center for the nucleus, and inside the nucleus, write the element symbol "C" and its charge "-2." 2. Draw the first energy level as a circle around the nucleus. This shell can hold up to 2 electrons. Place 2 electrons (represented as small dots or x's) on this shell. 3. Draw the second energy level as another circle around the first. This shell can hold up to 8 electrons. However, in this case, we only have 6 remaining electrons. Place these 6 electrons on this shell. The resulting Bohr diagram will show the carbon anion with its -2 charge in the nucleus and two filled electron shells, with 2 electrons on the first shell and 6 electrons on the second shell.

Key concepts

Atomic Number

The atomic number of an element is a fundamental property that defines the element and its position in the periodic table. It represents the number of protons found in the nucleus of an atom of the element. Each element has a unique atomic number. For example, the atomic number of carbon is 6, indicating it has 6 protons in its nucleus.

This number not only helps identify the element but also indicates the element's basic chemical properties. Knowing the atomic number allows us to find the element on the periodic table and also deduce information about electron configuration in a neutral atom, which in absence of ions, will have equal numbers of protons and electrons.

Bohr Model

The Bohr Model is a simple way to visualize atomic structure and electron arrangements that was developed by Niels Bohr in 1913. It represents atoms as having electrons orbiting the nucleus in well-defined paths called electron shells or energy levels. These concentric circles around the nucleus depict the different shells, each with a certain capacity for electrons.

In the case of carbon, with an atomic number of 6, according to the Bohr Model, the first shell (K-shell) can hold a maximum of 2 electrons, while the second shell (L-shell) can hold up to 8 electrons. This model is particularly useful in understanding the distribution of electrons in an atom's ground state and helps us visualize how electrons are arranged based on energy levels.

Anion

An anion is a type of ion that carries a negative charge. This occurs when an atom gains one or more electrons, resulting in more electrons than protons. The gain of electrons increases the overall negatively charged electron cloud around the nucleus, hence bestowing the ion with a negative charge.

In our example, carbon with 6 protons and 8 electrons, forms a carbon anion. Normally, a neutral carbon atom would have 6 electrons balancing its 6 positive protons. However, in this scenario, it has gained 2 extra electrons, leading to an anionic charge of \(-2\). Anions play a significant role in chemical reactions, especially in forming compounds like salts.

Electron Configuration

Electron configuration describes the arrangement of electrons in an atom's orbitals and shells. The electrons are distributed across different energy levels according to certain rules, primarily the Aufbau principle, which states that electrons fill the lowest available energy levels first.

For carbon, with a standard configuration of \(1s^2 2s^2 2p^2\), it has its first 2 electrons in the 1s subshell and the next 4 distributed as \(2s^2 2p^2\). When carbon becomes an anion with a \(-2\) charge by gaining 2 electrons, the electron configuration becomes \(1s^2 2s^2 2p^4\).

• The first shell is filled with 2 electrons in the 1s orbital.
• The second shell then fills as many electrons as allowed, here with four more electrons in the 2s and 2p orbitals.

Understanding electron configuration aids in predicting an element's chemical behavior and reactivity.