Understanding the Lothar Meyer Plot

The Lothar Meyer plot, also known as the atomic volume curve, is a graph that plots the atomic volume of elements against their atomic weights. Atomic volume is defined as the volume occupied by one mole of an element and is calculated using the formula:

$Atomic Volume = \frac{Molar Mass}{Density}$

This plot was historically significant in the development of the periodic table as it revealed periodic trends. The graph shows peaks and troughs, which correspond to specific groups of elements with particular properties.

Step 1: Identify the Pattern on the Graph

When you examine the Lothar Meyer curve, you will observe that the atomic volume generally increases as you move down a group. More importantly, the graph has distinct peaks. These peaks represent elements that have the largest atomic volumes in their respective periods.

Step 2: Relate Peaks to Element Properties

Elements with the largest atomic volumes are those with the lowest densities and often the largest atomic radii within their period. These elements are characterized by having a single electron in their outermost shell, which results in weaker metallic bonding and less efficient packing of atoms, leading to lower density and higher volume.

Step 3: Determine Which Group Fits This Description

Let's evaluate the options based on their position in the periodic table and their properties:

Halogens: These elements have relatively small atomic volumes. They are non-metals and tend to have higher densities and smaller atomic sizes compared to metals in the same period. They do not occupy the peaks.
Noble Gases: These are monatomic gases with very low densities and are known to have the largest atomic sizes in their respective periods. However, Lothar Meyer's original work was based on solid elements, and noble gases (which are gases at room temperature) were not included in his initial plot. Their atomic volumes are large, but they are not the peaks on the classic Meyer curve.
Alkaline Earth Metals (Group 2): These metals have two valence electrons, leading to stronger metallic bonding than their neighboring Group 1 elements. This results in higher densities and smaller atomic volumes. They are found in the troughs or rising parts of the curve, not at the peaks.
Alkali Metals (Group 1): These elements (Li, Na, K, Rb, Cs) have one valence electron. This leads to weak metallic bonding, low densities, and large atomic sizes. In every period, the alkali metal has the largest atomic volume, placing it at a distinct peak on the Lothar Meyer plot.

Final Answer

The peaks in the Lothar Meyer plot are occupied by the alkali metals.

Related Topics & Formulae

Key Formulae

Atomic Volume: $V_{atomic} = \frac{M}{ρ}$
Where $M$ is the molar mass (g/mol) and $ρ$ is the density (g/cm³).

Related Periodic Trends

Atomic Radius: Increases down a group, decreases across a period.
Metallic Character: Increases down a group and decreases across a period. Alkali metals are the most metallic elements.
Ionization Energy: The energy required to remove an electron. It is lowest for alkali metals, which is consistent with their single valence electron and large atomic size.

Theory: Significance of the Plot

Lothar Meyer and Dmitri Mendeleev independently developed periodic classifications of elements. Meyer's plot visually demonstrated the periodic law, which states that the properties of elements are a periodic function of their atomic weights (modern version: atomic numbers). The repeating pattern of peaks (alkali metals) and troughs (transition metals) provided strong graphical evidence for this law and helped predict the properties of yet-to-be-discovered elements.