Foundations of Chemistry. Philippa B. Cranwell

are the d block elements. This area includes 10 groups of elements from Sc to Zn in the first row of the d block. These elements are all metals and those in Groups 3-11 are often referred to as transition elements. The elements in the group headed by zinc (Group 12) are not transition elements.

At the bottom of the periodic table are the two rows of elements that form the f block. The elements in these two rows are called the lanthanides and actinides and have electrons filling the f orbitals. In total, f orbitals can hold 14 electrons, as there are 7f orbitals. A discussion of these orbitals is beyond the scope of this book.

      Worked Example 1.5

      Give the ground state electron configuration for .

       Solution

       has atomic number 16 and mass number 32. Therefore, a neutral atom of S has 16 protons, 16 electrons, and 16 neutrons. When putting the electrons into the orbitals, it is important to always start with the lowest‐energy orbital.

      Electrons are placed in the energy levels starting at the lowest energy level (1s) in order of increasing energy (Aufbau principle). When filling the third shell, electrons are firstly placed in the 3s orbital, as this has the lowest energy in the third shell, followed by four electrons in the 3p orbitals. However, when putting the remaining four electrons in the 3p orbitals, each p orbital is filled with one electron first (Hund's rule). When each p orbital is half full, there is one electron left over, and it is at this point that the electrons are paired. When they are paired, they have opposing spins, which in this case is represented by drawing each half‐arrow in opposite directions, fulfilling the requirements of the Pauli exclusion principle.

      The ground state electronic configuration of sulfur can be written as 1s²2s²2p⁶3s²3p⁴.

      The reason we say ‘ground state’ electron configuration is because ‘excited states’ can also exist. The discussion of excited states is beyond the scope of this book but is discussed at degree level.

      Worked Example 1.6

      Give the ground state electron configuration for .

       Solution

       has atomic number 19 and mass number 39, therefore in a neutral atom there are 19 protons, 19 electrons, and 20 neutrons.

      Starting at the lowest energy level, electrons are placed in the energy levels in order of increasing energy. When the third shell is reached, the electrons are firstly placed in the 3s orbital, as this is the lowest energy in the third shell, followed by six electrons in the 3p orbitals. There is one electron left over, and this is put into the 4s orbital because this is lower in energy than the 3d orbitals. This explains why potassium is an s‐block element, as the highest energy electron is in an s orbital.

      The ground state electronic configuration of potassium can be written as 1s²2s²2p⁶3s²3p⁶4s¹ or [Ar] 4s¹.

      Worked Example 1.7

      Give the ground state electron configuration for scandium.

       Solution

       has atomic number 21 and mass number 45. Therefore, in a neutral atom of Sc, there are 21 protons, 21 electrons, and 24 neutrons. As with the other examples, and following the Aufbau principle, Hund's rule, and the Pauli exclusion principle, the ground state electronic configuration of scandium can be written as 1s²2s²2p⁶3s²3p⁶4s²3d¹ or [Ar]4s²3d¹. Remember, the 4s orbital is filled before the 3d because it is lower in energy.

Quick‐check summary

       Atoms are made up of a central, dense region containing neutrons and protons surrounded by electrons in outer shells with different energies.

       Protons and neutrons have the same relative masses as each other whereas electrons are almost 2000 times lighter. Protons have a positive charge, electrons have a negative charge and neutrons are neutral. Isotopes of an element have the same number of protons (Z) but different numbers of neutrons and therefore different mass number (A).

       There are three main types of radioactive decay namely alpha-, beta- and gamma-.

       Electrons are arranged in orbitals according to their energies in the outer shells, or energy levels of the atom.

       The ground state electronic configuration of an atom can be defined by using the Aufbau principle, the Pauli exclusion principle, and Hund's rule.

       Each successive element has one more proton in the nucleus and one more electron in its outer shell. The different areas of the periodic table (s block, p block etc) are characterised by the type of orbitals in the outer shells being filled by electrons.

End‐of‐chapter questions

      1 What are the relative mass and charge of a proton, a neutron, and an electron?

      2 How many protons, neutrons, and electrons do the following atoms and ions contain?

      3 Define the term isotope. Include an example in your answer.

      4 Zinc exists as five naturally occurring isotopes: 64Zn, 66Zn, 67Zn, 68Zn, and 70Zn, with abundances 49.2%, 27.7%, 4.0%, 18.5%, and 0.6%, respectively. Calculate the average relative atomic mass of zinc.

      5 What are the three types of radiation that can be emitted by radioisotopes? Explain the difference between each type, and give any relevant equations.

      6 222Rn undergoes alpha decay. Give the equation for this process.

      7 Draw a clearly annotated diagram showing the shells of electrons in the following elements:ChlorineCalciumNeonCarbon

      8 On a clearly annotated diagram, draw and label:A 1s orbitalThree 2p orbitalsFive 3d orbitals

      9 Write the ground state electronic configurations for the following atoms or ions:SSrSe2−CoMnMg2+

      10 State the elements that have the following ground state electronic configurations:1s22s22p21s22s22p63s23p31s22s22p63s23p63d104s24p6[Ar]3d54s1

2 Chemical bonding

      At the end of this chapter, students should be able to:

       Describe different types of bonding using