Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 61

Figure 1.3 shows the arrangement of all 118 known elements in the periodic table. The elements are distributed over 18 columns and 7 rows. The elements are arranged according to atomic number, which increases from left to right and top to bottom. The atomic number equals the number of protons present in a neutral atom and therefore determines the position of the element in the periodic table.

Figure 1.3 The standard modern form of the periodic table. Source: University of Reading. Public Domain.

It is best to approach reading the periodic table like a book: start at the top left, and finish at the bottom right.

The rows across the periodic table are called periods, and there are seven periods numbered from one to seven. The columns down the periodic tables are called groups, and there are 18 groups in total, but their naming usually runs from one to eight. All of the elements underneath hydrogen (H) are in Group 1, and beneath beryllium (Be) they are in Group 2. The groups in the middle of the periodic table, from scandium (Sc) to zinc (Zn), are called the d‐block elements and are sometimes referred to by group numbers (i.e. Groups 3 to 12 in the 1-18 numbering system). The elements below boron (B) are in Group 3 (or Group 13), below C are in Group 4 (or Group 14), etc. up to those below helium (He), which are called Group 8 (sometimes called Group 0 or Group 18). Elements that exist in the same group have broadly similar chemical properties, due to having the same number of electrons in their outermost shell.

In some textbooks, you may see Groups 1–8 numbered as Groups 1–18, where the d‐block elements are numbered 3–12.

The periodic table is roughly divided by a zig‐zag line that splits the table into two parts. The elements to the right of the zig‐zag line are non‐metals, and those to the left of the line are metals. There are many more metals than non‐metals in the periodic table. Whether an element is a metal or non‐metal has an impact upon its properties. In addition, the periodic table is split into four distinct areas: the s block, the p block, the d block, and the f block (Figure 1.3). These areas relate to the orbital in which the outermost electron resides, and will be discussed further in Section 1.2.4.

Metals tend to be lustrous, malleable, sonorous when struck, ductile, and good conductors of heat and electricity. Metals are often solid, with a high melting and boiling point, although the one notable exception is mercury (Hg). Metals usually have a high density and can be heavy. In comparison, non‐metals tend to be dull, brittle, and poor conductors of heat and electricity, and they generally have lower melting and boiling points than metals. Elements that are close to the zig‐zag line exhibit atypical properties and are sometimes referred to as metalloids. For example, silicon (Si) exhibits properties that would be expected for both a metal and a non‐metal.

The bonding properties of metals and non‐metals will be discussed in Chapter 2.