Atomic Number and Periodic Table

Explain how an element's precise position in the periodic table relates to the arrangement of its electrons and its atomic number.

Describe the structure of the periodic table, noting that elements are arranged in order of increasing atomic number so that elements with similar properties form vertical columns called groups.

Understand that the table is described as periodic because similar chemical properties occur at regular intervals.

Explain that electrons occupy specific energy levels (shells), systematically filling the lowest available energy levels first.

Identify that elements in the same group possess the same number of electrons in their outermost shell, which directly dictates their similar chemical properties.

Represent the electronic structure of the first 20 elements using numerical notation.

Predict the possible reactions and probable reactivity of different elements based entirely on their position in the periodic table.

Explain how the discovery of isotopes forced a critical change in Mendeleev's original periodic table arrangement.

Describe how Mendeleev initially arranged elements by relative atomic mass, which resulted in some elements appearing in inappropriate groups.

Understand how arranging elements by atomic number resolved Mendeleev's inconsistencies, recognizing that most elements occur as a mixture of isotopes.