According to the Bohr atomic model, a new electron shell is added each time we descend a group, positioning the valence electrons at higher energy levels, farther from the nucleus. In contrast, as we move down a group, the atomic radius increases. This increased attraction draws the electron shells closer to the nucleus. As the proton number increases, its effect outweighs that of the added electrons, leading to a stronger electrostatic attraction between the positively charged protons and the negatively charged electrons. This decrease results from the simultaneous addition of electrons and protons to the atom. The atomic size, or atomic radius, of elements gradually decreases as we move from left to right across a period.

The diagram below offers a simplified visualisation of these trends as they appear in the periodic table These patterns arise due to the similar atomic structures of the elements within their respective groups or periods and the inherent periodic nature of these elements. Emerging from the unique arrangement of the periodic table, these trends provide chemists with an indispensable tool to quickly predict an element's properties. These individual trends collectively influence an element's reactivity. Major periodic trends include atomic radius, state of matter at room temperature, melting point, metallic character, electronegativity, and ionisation energy. The term 'periodicity,' as mentioned in Module 1: Properties and Structure of Matter in the Year 11 Preliminary HSC syllabus, refers to these reoccurring trends observed within the periodic table.

Periodic trends are specific patterns that emerge in the periodic table, illustrating various characteristics of elements, including their size and electronic properties. This classification system provides an efficient way to understand the shared properties and behaviors of the elements in the periodic tableĤf – subshell progressively being filled in the lanthanoidsĥf – subshell progressively being filled in the actinoids

The f block encompasses the lanthanides and actinides.

The d block is reserved for elements commonly known as 'transition metals.'.

The s and p blocks house what we typically refer to as the 'main group elements.'.

This classification harkens back to our exploration of the Schrödinger model and the SPDF electron configuration notation, serving as a handy tool to categorise elements based on their highest energy subshell configuration. These categories are assigned based on the sub-shell that accommodates the final electron in an element's atomic structure. The periodic table is split into four blocks: s, p, d, and f. Therefore, elements in Group 1 possess a single valence electron, conferring them with a valency of +1, and so forth. Elements in the s and p blocks are grouped according to the number of valence electrons in their outer shell. Conversely, Group 1 houses the alkali metals, a collection of highly reactive elements that engage in vigorous reactions with water. Group 18, for instance, is made up of the noble gases, a set of colorless, odorless, and largely unreactive elements. The modern table hosts 18 groups, with elements within the same group generally sharing similar properties. The columns of the periodic table are known as groups.

Element 115, Moscovium, and element 117, Tennessine, are named after Moscow, Russia, and Tennessee, USA, respectively, in recognition of the scientists and institutions that contributed to their discovery.

Element 113, Nihonium, was named by Japanese researchers, as 'Nihon' is the Japanese name for Japan.

Elements often derive their names from places or people associated with their discovery: The length of periods in the modern periodic table can vary: the first period comprises only hydrogen and helium, while periods 6 and 7 are extended, necessitating that many of their elements be placed beneath the main body of the table. As we move from left to right across a period, each successive element has one more proton than its predecessor. The rows in the modern periodic table are referred to as periods, echoing the nomenclature used in Mendeleev's original table. Despite these modifications, the fundamental structure of rows and columns, reminiscent of Mendeleev's design, is preserved as it reflects the inherent order of the elements. The modern periodic table, illustrated above, expands upon Mendeleev's original categorisation of 63 elements by arranging the elements according to increasing atomic number rather than atomic mass.

Valence electron trend periodic table