Consider the stable elements through lead (Z = 82). In how many instances are the atomic weights of the elements out of order relative to the atomic numbers of the elements?

Verified step by step guidance

1. Identify the atomic weights and atomic numbers of all stable elements up to lead (Z = 82).
2. Arrange the elements in order of increasing atomic number and note their corresponding atomic weights.
3. Compare the atomic weights of each element with those of the elements immediately preceding and succeeding it in the list.
4. Count the number of instances where an element has a higher atomic number but a lower atomic weight than the element that follows it.
5. Summarize the total number of such instances to find the answer.

Key Concepts

Atomic Number

The atomic number of an element is the number of protons found in the nucleus of its atoms, which determines the element's identity and its position in the periodic table. Elements are arranged in order of increasing atomic number, which reflects their increasing positive charge and the number of electrons in a neutral atom.

Atomic Weight

Atomic weight, or atomic mass, is the weighted average mass of an element's isotopes, measured in atomic mass units (amu). It reflects the mass of an atom relative to the mass of carbon-12 and can vary due to the presence of isotopes, which are atoms of the same element with different numbers of neutrons.

Periodic Trends

Periodic trends refer to the patterns observed in the properties of elements as one moves across or down the periodic table. These trends include variations in atomic size, ionization energy, and electronegativity, and they can also affect the relationship between atomic number and atomic weight, leading to instances where atomic weights do not increase consistently with atomic numbers.