Atoms and Elements

Introduction to Atoms and Elements

Atoms are the fundamental building blocks of matter. Understanding the structure and properties of atoms is essential for studying chemistry, as all elements and compounds are composed of atoms. There are about 91 naturally occurring elements, and scientists have synthesized over 20 additional elements.

• Atom: The smallest identifiable unit of an element that retains its chemical properties.

• Element: A pure substance consisting of only one type of atom.

• Example: Oxygen (O), Carbon (C), and Gold (Au) are elements, each made up of their respective atoms.

Atomic Structure

An atom consists of a dense nucleus surrounded by an electron cloud. The nucleus contains most of the atom's mass and all of its positive charge, while the electron cloud is a region of empty space where negatively charged electrons are dispersed.

• Nucleus: Contains protons and neutrons; responsible for the atom's mass and positive charge.

• Electron Cloud: Surrounds the nucleus; contains electrons, which are negatively charged and occupy most of the atom's volume.

• Example: In a hydrogen atom, the nucleus contains one proton, and one electron is found in the electron cloud.

Subatomic Particles

Atoms are composed of three main subatomic particles: protons, neutrons, and electrons. Each particle has distinct properties, including mass and electrical charge.

• Proton: Located in the nucleus; has a positive charge.

• Neutron: Located in the nucleus; has no charge (neutral).

• Electron: Located in the electron cloud; has a negative charge.

• Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

The mass of protons and neutrons is nearly identical and much greater than that of electrons. The atomic mass unit (amu) is commonly used to express these masses.

• Proton mass: kg ( amu)

• Neutron mass: kg ( amu)

• Electron mass: kg ( amu)

Electrical charge is a fundamental property of subatomic particles. Protons and electrons have charges of equal magnitude but opposite sign, while neutrons are neutral.

• Proton: Relative charge = +1; Actual charge = C

• Neutron: Relative charge = 0; Actual charge = 0 C

• Electron: Relative charge = -1; Actual charge = C

• Example: In a neutral atom, the number of protons equals the number of electrons, resulting in no net charge.

Electrical charges interact according to fundamental physical laws:

• Opposite charges attract each other (e.g., protons and electrons).

• Like charges repel each other (e.g., two protons or two electrons).

• When equal numbers of positive and negative charges are present, the net charge is zero.

Comparison Table: Subatomic Particles

The following table summarizes the key properties of protons, neutrons, and electrons:

Self-Assessment Table

Use the following table to reflect on your understanding of key topics from this lecture:

Additional info: The atomic mass unit (amu) is defined as one twelfth the mass of a carbon-12 atom. The charge of a proton and electron is fundamental to chemical bonding and reactions. Synthetic elements are created in laboratories and are typically unstable.