Problem 116 - Chemistry and Chemical Reactivity

Question

How many electrons are in a strontium atom (Sr)? Does an atom of Sr gain or lose electrons when forming an ion? How many electrons are gained or lost by the atom? When Sr forms an ion, the ion has the same number of electrons as which one of the noble gases?

Step-by-Step Solution

Answer

An Sr atom has 38 electrons. It loses 2 electrons to form Sr²⁺, having the same electrons as krypton.

Step 1: Find Atomic Number of Strontium

Strontium (Sr) is an element in the periodic table. To find the number of electrons in a neutral Sr atom, look at its atomic number. Strontium has an atomic number of 38, which means a neutral strontium atom has 38 electrons.

Step 2: Determine Strontium's Ion Formation

Strontium belongs to Group 2 of the periodic table, known as alkaline earth metals. Elements in this group typically lose electrons to form ions. Strontium loses 2 electrons when it forms an ion (Sr²⁺).

Step 3: Calculate the Electrons in Strontium Ion

When strontium loses 2 electrons, the Sr ion will have fewer electrons than its neutral state. Thus, the Sr²⁺ ion will have 38 - 2 = 36 electrons.

Step 4: Identify the Noble Gas with the Same Electron Count

With 36 electrons, the Sr²⁺ ion has the same number of electrons as the noble gas krypton (Kr), which also has 36 electrons.

Key Concepts

Strontium

Strontium is a chemical element symbolized by Sr, and it is located in Group 2 of the periodic table, which includes the alkaline earth metals. It possesses an atomic number of 38. This number represents the count of protons in strontium as well as the number of electrons in a neutral atom.
In their natural state, these electrons are organized in a pattern around the nucleus, determining the electron configuration of the atom. Strontium’s electron configuration is typically written as \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2\). This configuration illustrates how the electrons fill the atomic orbitals based on different energy levels in a specific order known as the Aufbau principle.
Understanding the electron configuration of strontium is vital for predicting how it behaves in chemical reactions, especially when forming ions.

Ions

Ions are charged particles formed when atoms lose or gain electrons. The creation of ions alters the original electron configuration, leading to a charged state rather than a stable, neutral one.
Strontium, being part of the alkaline earth metals, naturally forms ions by losing electrons. Specifically, it loses 2 electrons to form an \(Sr^{2+}\) ion. This loss of electrons results in a positively charged ion, as the positive charge from the protons exceeds the negative charge of the electrons.
The process of ion formation is crucial for understanding chemical bonding and interactions. Strontium's tendency to form \(Sr^{2+}\) ions allows it to readily participate in ionic bonds with negatively charged ions (anions), creating compounds like strontium chloride (SrCl₂) or strontium carbonate (SrCO₃).
In essence, the formation of ions like \(Sr^{2+}\) is significant for the chemistry of strontium and its role in forming stable compounds.

Noble gases

Noble gases are a group of elements located in Group 18 of the periodic table. They are characterized by having a complete outer electron shell, making them very stable and largely non-reactive.
For example, krypton (Kr), a noble gas, has a full set of 36 electrons. The stability of noble gases stems from their electron configurations, which do not require gaining or losing electrons to achieve a stable state.
When strontium forms a \(Sr^{2+}\) ion by losing 2 electrons, it attains an electron count that mirrors the stable outer shell of krypton. Thus, the \(Sr^{2+}\) ion resembles the electron configuration of a noble gas, which explains its stability in ionic forms.
By adopting an electron arrangement similar to that of noble gases, ions like \(Sr^{2+}\) gain enhanced stability in chemical reactions. This mimicry of noble gas electron configurations is a common feature of metals that form cations.