Question

Deseribe the changes in properties (from metals to nonmetals or from nonmetals to metals) as we move (a) down a periodic group and (b) across the periodic table from left to right.

Short answer

Down a group, properties become more metallic; across a period, they change from metallic to non-metallic.

Step-by-step solution

Understanding the Periodic Table

Before we dive into the changes in properties, it's essential to understand that the periodic table is arranged in groups (vertical columns) and periods (horizontal rows). Metals are typically located on the left side and center of the table, while nonmetals are on the right side.

Analyzing Down a Group

As you move down a group in the periodic table, elements typically become more metallic. This means they have a greater tendency to lose electrons during chemical reactions, exhibit higher electrical conductivity, and possess a shinier appearance. For instance, in Group 1, lithium (at the top) is less metallic compared to cesium (at the bottom).

Analyzing Across a Period

As you move from left to right across a period, elements generally change from metallic to non-metallic. This is due to an increase in the number of electrons in the outer shell, resulting in higher ionization energies and electronegativity. For example, in Period 3, sodium (a metal) is on the left, while chlorine (a nonmetal) is further to the right.

Consideration of Metalloid Transition

In the transition across a period, be aware that there are elements known as metalloids, which exhibit properties intermediate between metals and nonmetals. These elements, such as silicon and germanium, act as a bridge between the two classes as you move across a period.

Key concepts

Metallic Properties

Metallic properties define the characteristics commonly associated with metals, like being shiny, malleable, ductile, and good conductors of electricity and heat. As we move across the periodic table, particularly down a group, elements increasingly exhibit metallic behavior.
This is because electrons are more easily lost from an atom as the atomic number increases, leading to the characteristic shine and conductivity of metals. As you go from lithium to cesium in Group 1, for example, you see an increase in metallic properties.

• Luster - Metals typically have a distinctive shiny appearance.
• Conductivity - Metals can conduct electricity and heat efficiently.
• Malleability and Ductility - Metals can be hammered into thin sheets or drawn into wires without breaking.

These properties all stem from the ability of metal atoms to lose electrons easily and form positive ions.

Nonmetallic Properties

Nonmetals are on the right side of the periodic table. They tend to have higher ionization energies and electronegativities compared to metals, and they usually gain electrons during chemical reactions.
Nonmetals are often gases or brittle solids and do not conduct electricity well. When moving from left to right across a period, elements transition from metals to nonmetals.

• Variety of States - Nonmetals can be gases (like oxygen and nitrogen), liquids (like bromine), or solids (like sulfur).
• Lower Density and Melting Points - Nonmetals usually have lower densities and lower melting points compared to metals.
• Poor Conductivity - Nonmetals are poor conductors of heat and electricity.

This mix of properties helps distinguish nonmetals from their metallic counterparts.

Metalloids

Situated between metals and nonmetals on the periodic table, metalloids exhibit a unique combination of both metallic and nonmetallic properties. These elements, such as silicon and germanium, serve as a bridge between the two classes.
Chemically, metalloids tend to form amphoteric oxides and can have varying degrees of metallic and non-metallic characteristics depending on the conditions.

• Intermediate Conductivity - Metalloids often exhibit semi-conductive properties, which make them valuable in electronics, especially in the semiconductor industry.
• Variable Appearance - Some metalloids like silicon can be shiny like metals, yet others can have a more dull, non-metal-like appearance.
• Chemical Behavior - Metalloids can react chemically both as metals and nonmetals.

Understanding metalloids is crucial since they offer a balance of properties used in a variety of applications.

Chemical Reactivity

Chemical reactivity refers to how quickly an element can engage in a chemical reaction. This reactivity changes as you move across the periodic table.
For metals, reactivity generally decreases across a period but increases down a group. For nonmetals, the reactivity increases across a period and decreases down a group.

• Metal Reactivity - More reactive metals are located at the bottom-left of the periodic table, like francium and cesium.
• Nonmetal Reactivity - Highly reactive nonmetals, such as fluorine and oxygen, are found at the top-right of the periodic table.
• Group Trends - Elements in the same group often exhibit similar reactivity because of their comparable electronic configurations.

This variation in reactivity across the periodic table influences how elements interact and form compounds.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom or ion. It is a critical factor influencing an element's chemical properties and its tendency to gain or lose electrons.
As you move from left to right across a period, ionization energy typically increases. This is due to increased nuclear charge attracting electrons more strongly, making them harder to remove.

• Increasing Across a Period - It becomes more difficult to remove an electron as you travel from left to right across the periodic table.
• Decreasing Down a Group - As you move down a group, the ionization energy decreases since the outer electrons are further away from the nucleus.
• Significance - The ionization energy helps explain why nonmetals are more likely to gain electrons to achieve full outer shells.

A deep understanding of ionization energy assists in predicting an element's behavior in chemical reactions.