Question

Briefly describe the structure of an atom. What determines the atom's atomic mumber? What determines its atomic mass number? Under what conditions are two atoms different isotopes of the same element? What is a molecule?

Short answer

An atom is made of protons, neutrons, and electrons. Atomic number is based on protons, and mass number is protons plus neutrons. Isotopes have different neutrons; molecules are bonded atoms.

Step-by-step solution

Understanding the Structure of an Atom

An atom consists of a nucleus made up of protons and neutrons, surrounded by a cloud of electrons. The electrons orbit the nucleus in various energy levels.

Atomic Number Determination

The atomic number of an atom is determined by the number of protons in its nucleus. The atomic number uniquely identifies a chemical element.

Atomic Mass Number Determination

The atomic mass number is the total count of protons and neutrons in an atom's nucleus. It approximates the atomic weight of the atom.

Identifying Isotopes

Isotopes are variants of the same chemical element that have the same number of protons but different numbers of neutrons. This results in different atomic mass numbers.

Defining a Molecule

A molecule is a group of two or more atoms that are chemically bonded together. Molecules can be formed by the same or different elements.

Key concepts

Atomic Number

The atomic number is a fundamental concept when it comes to understanding the structure of an atom. If you think of an atom as a tiny solar system, the nucleus is like the sun. It's made up of protons and neutrons while electrons orbit around it. The atomic number is defined as the number of protons in the nucleus of an atom.
This number is crucial because it determines the chemical identity of the element. For example, all carbon atoms have an atomic number of 6, meaning they each contain 6 protons.

• The atomic number is written as a subscript before the element symbol, like this: \(_{6}\text{C}\).
• It is used to organize the elements in the periodic table.
• Whenever you look at the periodic table, you can identify an element by its atomic number.

Understanding the atomic number helps you know "what" the element is, making it an essential tool in chemistry.

Atomic Mass Number

The atomic mass number is another fundamental concept of atomic structure, representing the total number of protons and neutrons in an atom's nucleus. Electrons are so light that they don't significantly affect the atomic mass number. Therefore, the formula is simply: \[\text{Atomic Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}\] This sum gives us an approximation of the atom's mass because the mass of a neutron is roughly equal to that of a proton.
The unit used for atomic mass is called the atomic mass unit (amu). Each proton and neutron weighs about 1 amu.

• The atomic mass number is usually written as a superscript before the element symbol, e.g., \(^{12}\text{C}\).
• It's important in distinguishing between different isotopes, as they each have unique atomic mass numbers.
• Unlike atomic number, the atomic mass number can vary within elements due to different isotopes.

The atomic mass number gives us a better understanding of the atom's size and variation between elements and isotopes.

Isotopes

Isotopes are fascinating because they show how atoms of the same element can have slight differences. An isotope is any variant of an element characterized by a differing number of neutrons while maintaining the same number of protons. This leads to a different atomic mass number.
For example, carbon has two stable isotopes: carbon-12 and carbon-13.

• Carbon-12 has 6 protons and 6 neutrons, giving it an atomic mass number of 12.
• Carbon-13 has 6 protons and 7 neutrons, resulting in an atomic mass number of 13.

What’s consistent with isotopes is the atomic number, which remains constant because the number of protons doesn't change. Isotopes are significant in various scientific applications such as radiocarbon dating and medical diagnostics.
Ultimately, understanding isotopes broadens our knowledge of atomic diversity and behavior.

Molecule

A molecule is an assembly of two or more atoms that are chemically bonded together. This bonding configuration gives molecules distinct properties and functions. They can be made up of the same type of atoms, known as diatomic molecules such as \(\text{O}_2\), or different types of atoms, like in water \(\text{H}_2\text{O}\).

• Covalent bonds are the typical chemical bonds in molecules where atoms share electrons.
• Molecules take various shapes and sizes based on how atoms bond and the number of atoms involved.

The formation of molecules is key in understanding chemical reactions and properties of substances. When atoms bond to form molecules, they achieve more stability by completing their outer electron shells.
This concept is a cornerstone in chemistry and underlies everything from the air we breathe to the complex reactions that sustain life.