Question

Criticize each of the following statements: (a) The Rutherford experiment confirmed the presence of electrons in an atom. (b) A period is that segment of the periodic table in which elements are arranged by similar chemical properties. (c) Isotopes have the same mass number. (d) The molecule \(\mathrm{Be}_{3} \mathrm{~N}_{2}\) is triberylium dinitride.

Short answer

Based on the given step-by-step solution, provide a short answer for each criticized statement below: a) Rutherford's experiment confirmed the presence of electrons in an atom. - This statement is not entirely correct. Rutherford's experiment confirmed the existence of a positively charged nucleus in an atom rather than the presence of electrons. b) In the periodic table, elements within the same period have similar chemical properties. - This statement is incorrect. Elements within the same period do not necessarily have similar chemical properties. Instead, elements within the same group exhibit similar chemical properties. c) Isotopes have the same atomic number and the same mass number. - The statement is incorrect. Isotopes have the same atomic number but different mass numbers. d) The correct name for the molecule \(\mathrm{Be}_{3} \mathrm{N}_{2}\) is "triberylium dinitride." - This statement is incorrect. The correct name for the molecule \(\mathrm{Be}_{3} \mathrm{N}_{2}\) is "beryllium nitride."

Step-by-step solution

(a) Understanding Rutherford experiment

Rutherford's experiment, also known as the gold foil experiment, focused on the structure of the atom. He aimed to provide experimental evidence to support or refute the then popular "plum pudding model" of the atom, which suggested that electrons were distributed evenly within a positively charged sphere. Rutherford directed alpha particles at a thin gold foil and analyzed the scattering patterns of these particles.

Criticizing statement (a)

This statement is not entirely correct. The Rutherford experiment did not confirm the presence of electrons in an atom. Instead, it confirmed that the positively charged nucleus exists at the center of the atom and that electrons orbit around it. The experiment helped to disprove the plum pudding model of the atom and paved the way for the development of the modern atomic model, which includes the presence of electrons.

Understanding periodic table and periods

The periodic table is a chart that organizes elements according to increasing atomic number and periodic trends in their physical and chemical properties. A period refers to a horizontal row in the periodic table.

Criticizing statement (b)

The statement is incorrect. In the periodic table, elements within the same period do not necessarily have similar chemical properties. Instead, elements within the same group (vertical columns) exhibit similar chemical properties due to the same number of valence electrons.

Definition of isotopes

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons in their nuclei. Consequently, isotopes have the same atomic number but different mass numbers.

Criticizing statement (c)

The statement is incorrect. Isotopes, by definition, do not have the same mass number. Instead, they have the same atomic number (number of protons) but different mass numbers (sum of protons and neutrons).

Understanding chemical naming conventions

In chemistry, there are specific naming conventions for chemical compounds. For example, when naming binary compounds (consisting of two different elements), the first element is typically named with a prefix to indicate the number of atoms present, followed by the second element with an "ide" ending.

Criticizing statement (d)

The statement is incorrect. The correct name for the molecule \(\mathrm{Be}_{3} \mathrm{N}_{2}\) is not "triberylium dinitride." According to the naming conventions, the proper name for this molecule is "beryllium nitride." While it may be tempting to use the prefixes "tri-" and "di-" in the name, they are not necessary in this case because the molecule is composed of single chemical units rather than multiple units of different elements.

Key concepts

Periodic Table Trends

Understanding the periodic table trends is fundamental for grasping how the characteristics of chemical elements are related and predictably vary. The periodic table is essentially a map of the elements, reflecting their electronic structure, which affects their chemical behavior.

One of the principal trends is the atomic size or atomic radius. This generally decreases across a period from left to right due to an increase in nuclear charge, pulling electrons closer. Conversely, the atomic radius increases down a group as additional electron shells are added. Another significant trend is electronegativity, which follows a similar pattern as atomic size, increasing across a period and decreasing down a group. Electronegativity reflects an atom's tendency to attract a shared pair of electrons.

Ionization energy, the energy required to remove an electron from an atom, usually increases across a period and decreases down a group. This occurs because atoms on the left side of the table are more willing to lose electrons to achieve a stable configuration, while those on the right are more inclined to hold onto their electrons.

Understanding these trends can illuminate why elements behave differently and how to predict their reactions. For instance, elements in the same group often have similar chemical properties because they have the same number of valence electrons, which are key players in chemical bonding.

Isotopes and Mass Number

Isotopes are versions of an element that have the same number of protons but differ in the number of neutrons. Since the number of protons (atomic number) defines an element, isotopes remain the same element but with varying mass numbers. The mass number is the sum total of protons and neutrons in an atomic nucleus.

For instance, carbon has isotopes with mass numbers of 12, 13, and 14, commonly denoted as Carbon-12, Carbon-13, and Carbon-14. Despite these differences in mass, all carbon isotopes behave chemically in the same way because they have the same number of protons and electrons, ensuring the same chemical properties.

Understanding isotopes is crucial, not just for chemical reactions but also for applications such as radiometric dating, nuclear medicine, and the study of environmental changes. Since isotopes can have different nuclear stabilities, some may be radioactive and are thus used to track processes over various scales of space and time.

Chemical Naming Conventions

Chemical naming conventions provide a standardized way for scientists to communicate about chemical compounds. These rules ensure that the chemical formula can be translated to a unique and universally understandable name.

Binary compounds, made up of two different elements, are named by combining the full name of the first element with a modified name of the second, which ends with the suffix -ide. Prefixes like di-, tri-, and tetra- are sometimes used for molecular compounds (those composed of nonmetals) to indicate the number of atoms present. Compounds formed from metals and nonmetals, however, typically do not require such prefixes if they're using the classical nomenclature, as the metal's oxidation state isn't always indicated with a prefix but can be with a roman numeral in parentheses.

It's vital to note that different types of compounds have different rules for naming. For example, ionic compounds often require knowledge of charge and oxidation states for proper naming. The mastering of naming conventions is an essential skill for interpreting and predicting the structure and reactivity of compounds.

Atomic Model

The atomic model has evolved significantly since the early ideas of indivisible particles. From Rutherford's model, which introduced a dense nucleus with electrons orbiting it, to the quantum mechanical model of the atom present today, each step has provided deeper insight into atomic structure.

After Rutherford's gold foil experiment, which led to the downfall of the plum pudding model, Niels Bohr proposed that electrons move in fixed orbital shells with quantized energies. However, modern quantum mechanics refined this further, replacing orbits with orbitals, regions of space where there is a high probability of finding an electron.

The current understanding reflects that the behavior of electrons in an atom is not entirely predictable, giving rise to quantum numbers that describe the probable location and energy state of an electron. With these advancements, scientists can predict atomic behavior, interactions, and the very nature of the chemical bonds that hold compounds together, adding a wealth of knowledge to both the theoretical and practical aspects of chemistry.