Write a symbol for each of the following neutral isotopes. Include the atomic number and mass number for each. (a) the alkali metal with 11 protons and a mass number of 23 (b) the noble gas element with 75 neutrons in its nucleus and 54 electrons in the neutral atom (c) the isotope with 33 protons and 40 neutrons in its nucleus (d) the alkaline earth metal with 88 electrons and 138 neutrons

The atomic number is a fundamental property of an element that can be used to uniquely identify it. It is denoted as the number of protons in the nucleus of an atom, and because atoms are electrically neutral, the atomic number also represents the number of electrons in a neutral atom. For instance, in the given exercise, sodium (Na) has an atomic number of 11, which means it consists of 11 protons and, consequently, 11 electrons when neutral. Understanding the atomic number is crucial in determining an element's position in the periodic table and predicting its chemical behavior.

When dealing with isotopes, the atomic number remains unchanged because isotopes are variants of a particular element that differ in neutron number while maintaining the same proton count. This characteristic is integral in distinguishing between elements and comparing isotopes of the same element.

The mass number is the sum of protons and neutrons in an atom's nucleus, symbolizing the total number of these subatomic particles, which contribute to most of the atom's mass. For example, arsenic (As) with a mass number of 73 has 33 protons and 40 neutrons. The mass number is crucial in differentiating isotopes of the same element, as isotopes can have the same atomic number but different mass numbers due to varying numbers of neutrons.

When representing isotopes, both the atomic number and the mass number are typically included to provide a full description. For instance, radium with 88 protons and 138 neutrons is represented with a mass number of 226. Understanding the concept of mass number is essential for tasks such as calculating the relative atomic mass of elements and predicting the behavior of isotopes in chemical reactions.

Alkali metals are a group of elements found in group 1 of the periodic table. They are characterized by having a single electron in their outermost energy level, which makes them highly reactive, especially with water. Examples of alkali metals include lithium (Li), sodium (Na), and potassium (K). In the exercise, sodium with 11 protons is identified as an alkali metal because of its position in group 1.

Reactivity of Alkali Metals

Alkali metals tend to lose their one valence electron easily to form cations with a charge of +1, resulting in typical properties like low melting points, low density, and high reactivity. As we move down the group, the reactivity of alkali metals increases due to the valence electron being further away from the nucleus and more easily lost during chemical reactions.

Noble gases form group 18 of the periodic table and are well-known for their lack of reactivity under standard conditions. This inert behavior is due to their electronic configuration; noble gases have their outermost energy levels fully occupied by electrons, resulting in a stable configuration. Helium (He), neon (Ne), argon (Ar), and xenon (Xe) are all examples of noble gases.

Stability of Noble Gases

The noble gas xenon, with 54 protons and 75 neutrons, as mentioned in the exercise, has a full set of electrons in its outer shell, which makes it nonreactive under normal circumstances. These gases are used in applications where non-reactivity is a desired property, such as in lighting and as inert gas shields in welding. They are also fascinating for scientific study, as some compounds of noble gases have been synthesized under special conditions.

The periodic table is a visual representation of all known elements organized by increasing atomic number and grouped by common chemical properties. Each row of the table, known as a period, corresponds to a higher energy level for electrons in an atom. The columns, known as groups or families, contain elements with similar reactivity and other chemical properties due to similar valence electron configurations.

Understanding the layout of the periodic table is vital for grasping how elements relate to each other. For example, alkali metals, which include sodium with 11 protons, are found in group 1, while noble gases like xenon with 54 protons are in group 18. The periodic table also provides information about atomic mass and shows patterns such as the reactivity of metals and the stability of noble gases. Therefore, it acts as a powerful tool for predicting chemical behaviors and understanding elemental relationships.