Question

Use a periodic table for this problem. (a) Which element has the electron configuration $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^2?$ (b) List two elements which have exactly two valence electrons.

Short answer

(a) Titanium (Ti), (b) Beryllium (Be) and magnesium (Mg).

Step-by-step solution

Understanding Electron Configuration

The given electron configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^2$. This needs to be matched to an element based on the number of electrons, which corresponds to the atomic number of the element.

Counting Electrons

To find the element, count the total number of electrons in the electron configuration: $$1s^2(2)+2s^2(2)+2p^6(6)+3s^2(2)+3p^6(6)+4s^2(2)+3d^2(2)=22$$ The atomic number 22 corresponds to the element titanium (Ti) on the periodic table.

Identifying Elements with Two Valence Electrons

Elements with two valence electrons typically end their electron configuration with $s^2$. Check the periodic table, particularly focusing on Group 2 (alkaline earth metals) and Group 12. Examples include beryllium (Be) and magnesium (Mg) in Group 2, and zinc (Zn) and cadmium (Cd) in Group 12.

Key concepts

Periodic Table

The periodic table is like a map for chemists. It organizes all known elements in a way that highlights their properties and relationships.
To use it effectively, you need to understand how it's structured. Each element is placed in a specific spot based on its atomic number, which is the number of protons in the nucleus of an atom.

Columns in the table are called groups, and they share similar chemical properties. For instance, the elements in Group 2 are known as the alkaline earth metals, which we'll discuss later.
Rows are referred to as periods, and as you move from left to right across a period, elements gain one more proton and electron. This predictable layout makes identifying elements based on their properties, like electron configuration, much simpler.

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a key role in chemical reactions. They determine how an element will react with others.
For example, elements with two valence electrons typically belong to either Group 2 or Group 12 of the periodic table. These electrons are ready to be lost in reactions, forming positive ions.

Knowing the valence electrons of an element helps predict its reactivity and the types of bonds it will form.

• Elements with a full outer shell are usually non-reactive, like the noble gases.
• Those with nearly full or nearly empty outer shells are often the most reactive, like the alkali metals or halogens.

Understanding valence electrons is vital for working through problems dealing with electron configurations.

Atomic Number

Every element on the periodic table has a unique atomic number. This number tells you how many protons are in the nucleus of an atom of that element.
Since atoms are neutral, the atomic number also gives you the number of electrons in a neutral atom. That's because the number of protons equals the number of electrons, balancing out the electric charges.

Atomic number is crucial for identifying elements. For example, in the problem given, by counting the electrons in the configuration, we matched the atomic number to titanium, which is 22. The atomic number organizes the periodic table and dictates the chemical behavior of an element.

Alkaline Earth Metals

Alkaline earth metals are a group of elements found in Group 2 of the periodic table. These metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
These elements all share the property of having two valence electrons, which means their electron configuration ends with "s²".

Due to their two valence electrons, they tend to lose these electrons easily, forming ions with a charge of +2. This makes them quite reactive, though not as much as Group 1 elements, the alkali metals.

• They are commonly found in compounds rather than in their elemental form.
• They are essential in various industries, such as construction and electronics.
• Magnesium and calcium are also vital for biological purposes, playing roles in bone structure and cellular processes.

Understanding alkaline earth metals, with their consistent properties, helps in predicting their behavior in reactions and their uses in real-world applications.