Question

State the number of valence electrons in each of the following groups as predicted from the periodic table: (a) Group IA/1 (b) Group \(\mathrm{IIIA} / 13\) (c) Group VA/15 (d) Group VIIA/17

Short answer

(a) 1, (b) 3, (c) 5, (d) 7

Step-by-step solution

Understanding Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom and determine its chemical properties. The periodic table is organized in such a way that elements in the same group (column) have the same number of valence electrons.

Group IA/1 Valence Electrons

Elements in Group IA/1, also known as the alkali metals, have 1 valence electron. This is because they have the electron configuration ending in \( ext{ns}^1\).

Group IIIA/13 Valence Electrons

Elements in Group \( ext{IIIA} / 13\) have 3 valence electrons. These elements end their electron configurations with \( ext{ns}^2 ext{np}^1\).

Group VA/15 Valence Electrons

Elements in Group VA/15 have 5 valence electrons. The electron configuration for these elements ends with \( ext{ns}^2 ext{np}^3\).

Group VIIA/17 Valence Electrons

Elements in Group VIIA/17, also known as the halogens, have 7 valence electrons. Their electron configurations end with \( ext{ns}^2 ext{np}^5\).

Key concepts

Alkali Metals

The alkali metals include the elements found in Group 1 (IA) of the periodic table. These elements, like lithium, sodium, and potassium, are characterized by having just one valence electron. This electron resides in the outermost electron shell, making these metals highly reactive.

Their electron configuration ends in \(\text{ns}^1\), meaning they have a single electron in their outermost s-sublevel. This lone electron is relatively easy to lose, which is why alkali metals tend to form positive ions when reacting with other elements. This group is key in chemical reactions and has a significant role in forming compounds.

Halogens

Halogens make up Group 17 (VIIA) of the periodic table and include elements such as fluorine, chlorine, and bromine. These elements have seven valence electrons, which makes them just one electron short of completing their outer shell. As a result, halogens are highly reactive, especially with alkali metals.

The electron configurations of halogens end in \(\text{ns}^2\text{np}^5\), indicating they need only one more electron to reach a stable octet (eight electrons in their outer shell). This propensity to gain an electron makes them eager participants in the formation of compounds, particularly salts with alkali metals.

Electron Configuration

Electron configuration is a shorthand notation that describes the distribution of electrons among the orbitals of an atom. This is essential for understanding the chemical behavior of elements.

For example, consider the alkali metals: their electron configuration ends as \(\text{ns}^1\), indicating one valence electron. In contrast, halogens have an electron configuration that ends in \(\text{ns}^2\text{np}^5\), showing seven valence electrons. Electron configurations help predict how elements will interact in chemical reactions, influencing the types of bonds they will form.

Periodic Table Groups

The periodic table is organized into columns known as groups, which are key to predicting the chemical properties of elements. Elements in the same group share similar valence electron configurations, which govern their reactivity and bonding behavior.

For instance, all members of Group 1 (alkali metals) have one valence electron, while Group 17 (halogens) possess seven valence electrons. By observing an element's group number, we can predict the number of valence electrons, anticipate how an element will bond, and understand its role in forming chemical compounds. This makes the periodic table an invaluable tool in chemistry.