Question

When an alkali metal forms an ion, what is the charge of the ion? What is the charge of an alkaline earth metal ion?

Short answer

Alkali metal ions have a +1 charge, and alkaline earth metal ions have a +2 charge.

Step-by-step solution

Identifying the Charge of Alkali Metal Ions

Alkali metals are the elements found in group 1 of the periodic table. These elements have a single valence electron in their outermost shell. When they form ions, alkali metals lose one electron and thus have a +1 charge. The resulting ion is a cation with a positive charge.

Determining the Charge of Alkaline Earth Metal Ions

Alkaline earth metals are located in group 2 of the periodic table. These elements have two valence electrons. Upon forming ions, alkaline earth metals lose both valence electrons to achieve a noble gas electron configuration resulting in a +2 charge. The produced ions are cations with a double positive charge.

Key concepts

Periodic Table Groups

The periodic table is a powerful tool for understanding the properties of elements, largely because it is organized by recurring trends or 'periodicity.' The table is divided into several groups based on similar chemical properties and the same number of valence electrons, which contribute to their similar behavior.

• Alkali metals, found in Group 1, are known for their reactivity and have a single valence electron. Examples include lithium (Li), sodium (Na), and potassium (K).
• The Alkaline earth metals reside in Group 2 and possess two valence electrons, making them also reactive, albeit less so than their neighbors in Group 1. This group includes elements such as beryllium (Be), magnesium (Mg), and calcium (Ca).
• Transition metals, in groups 3 through 12, have varying numbers of valence electrons and can form multiple ion charges.
• The rightmost groups consist of halogens and noble gases, each with distinctive reactive characteristics or a lack thereof, respectively.

Understanding the group placements helps predict how an element will behave when forming an ion, by indicating the likely charge the ion will carry based on the loss or gain of electrons.

Cation Formation

When elements form ions, they strive for the most stable electron configuration, often resembling the nearest noble gas. To achieve this, atoms can lose or gain electrons, creating ions.

Elements that lose electrons form positively charged ions called cations. A crucial point to understand is that cation formation occurs because atoms seek electrical neutrality; by losing valence electrons, they allow their positive nuclear charge to prevail:

• Alkali metals lose one electron, leading to a +1 cation.
• Alkaline earth metals lose two electrons, resulting in a +2 cation.

These ions have a full outer electron shell after losing their few valence electrons, making them more stable. The process requires energy to overcome the attraction between the electrons and the nucleus, which is why ionization energies play a role in how easily an atom forms a cation.

Valence Electrons

In the landscape of atomic structure, valence electrons play a pivotal role in the chemical nature of elements. These are the electrons found in the outermost shell of an atom and determine an element's ability to bond with others.

• Alkali metals have one valence electron, leading to straightforward reactions where they typically lose this lone electron to become stable.
• Alkaline earth metals, with two valence electrons, tend to lose both to achieve stability, thus forming a +2 cation.

The valence electrons are like the atom's 'handshake' in chemical interactions – they are both the greeting and the agreement that binds atoms together in compounds. That handshake can be a peaceful transfer, as is the case with ionically bonded compounds, or a shared arrangement in covalent bonds. Understanding the number of valence electrons in an element not only predicts the type of ion it will form but also its reactivity and the type of bonds it will prefer in compounds.