Element Blocks, Metals, and Non-metals

Two ways to read the same map

The table can be divided according to the type of subshell being filled, or according to the observable properties of elements. These divisions overlap but are not identical. For example, the p block contains metals as well as non-metals, whereas the d region is metallic. Reading both maps gives a more useful picture than learning either set of labels alone.

Main-group elements

The s-block metals have one or two outer s electrons. Removing those electrons commonly gives $1+$ ions for Group 1 or $2+$ ions for Group 2. Their low ionization enthalpies make electron loss comparatively easy. Because these metals react readily, they normally occur in compounds rather than as free elements.

Group 1 elements are alkali metals and Group 2 elements are alkaline earth metals. Their metallic character and common electron-loss reactivity generally increase down a group. Most compounds of these elements are predominantly ionic, although lithium and especially beryllium show important covalent character in some compounds. The first members are not perfect copies of the heavier members.

The p-block elements, together with the s-block elements, are called representative or main-group elements. Across a p-block section, the outer pattern changes from $n{s}^{2}n{p}^1$ to $n{s}^{2}n{p}^6$. The range includes metals on its left, non-metals on its right, and metalloids near the boundary.

Group 17 is the halogen family, with outer pattern $n{s}^{2}n{p}^5$, one electron short of a closed s–p shell. Group 16 is the chalcogen family, commonly associated with $n{s}^{2}n{p}^4$. Many of these elements gain or share electrons in compounds. This does not mean that an isolated Group 16 atom takes up two electrons with energy release at both steps; the complete formation of a compound must be considered.

Group 18 contains noble gases. Their filled outer arrangements make many simple chemical changes energetically unfavourable, so ordinary noble gases have very low reactivity. Helium’s shell is complete with $1s^2$, not eight electrons. A completed shell is the important feature.

Hydrogen is also exceptional. Its $1s^1$ configuration resembles the outer pattern of Group 1, and it can lose its electron in chemical descriptions. It can also gain one electron to complete its shell, resembling the halogens in that respect. Hydrogen is a non-metal and is not an ordinary alkali metal. Its separate position in some diagrams acknowledges its unique combination of properties.

Transition and inner-transition elements

In the central d region, electrons fill a subshell one shell inside the outer s shell. Many of these metals have several accessible oxidation states, form coloured ions, have unpaired electrons, and act as catalysts. Paramagnetism is attraction to a magnetic field associated with unpaired electrons; a catalyst changes a reaction rate without being consumed overall.

Zinc, cadmium, and mercury lie in Group 12 of the d region, but their common ions retain filled d subshells. They therefore do not show many typical transition-element features and are excluded by the usual strict definition. Also, colour, variable oxidation states, and catalysis are common features, not properties that every ion of every d-region element must show.

The detached f rows involve filling an f subshell two shell numbers below the period’s outer s shell. They contain metals with similar properties within each series. In the chapter’s layout the fourteen inserted entries are Ce–Lu and Th–Lr; the broader collective names lanthanoids and actinoids also commonly include La and Ac. Actinoids are radioactive, and the early members can show several oxidation states. Elements after uranium are called transuranium elements; many heavy members are prepared in very small quantities by nuclear reactions.

Metals, non-metals, and the boundary between them

A metal usually conducts heat and electricity well and can be reshaped without shattering. Malleability is the ability to be hammered into sheets; ductility is the ability to be drawn into wires. Most metals are solids at room temperature, but mercury is liquid. Gallium and caesium melt near room temperature. High melting point is common among metals, not part of an exceptionless definition.

Non-metals mostly occupy the upper right of the table, with hydrogen as a separate case. Many are gases or low-melting solids and conduct poorly, while solid non-metals are often brittle. Carbon and boron are important exceptions to simple low-melting generalisations. A single property is rarely enough to classify an unfamiliar sample reliably.

Metallic character broadly increases towards the lower left; non-metallic character broadly increases towards the upper right. These patterns connect to how easily atoms lose or attract electrons. They help with comparisons, but a diagonal comparison can involve competing trends and sometimes needs actual data.