The Nature of Matter and Atoms

Study Notes

All living things are made up of chemical compounds, which are the building blocks of life.
The human body uses substances from food and water to carry out chemical reactions that keep it alive.

The atom is the basic unit of matter, and it consists of subatomic particles: protons, neutrons, and electrons.
Atoms are incredibly small, with 100 million sulfur atoms lined up side by side being only about 1 centimeter long.
The concept of the atom originated from the Greek philosopher Democritus, who called the smallest fragment of any substance an atom, meaning "unable to be cut".

Protons and neutrons have roughly the same mass, but protons are positively charged, while neutrons carry no charge.
Strong forces bind protons and neutrons together to form the nucleus at the center of the atom.

Electrons are negatively charged particles with a much smaller mass than protons.
Electrons are in constant motion in the space surrounding the nucleus, and they are arranged in a series of shells or orbitals.
The number of electrons in an atom is equal to the number of protons, making the atom electrically neutral.

A pure substance that consists entirely of one type of atom is called an element.
Elements are represented by one or two-letter symbols, such as C for carbon, H for hydrogen, and Na for sodium.
The number of protons in the nucleus of an element is its atomic number, which determines its identity.
Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different mass numbers.
The atomic mass of an element is the weighted average of the masses of its isotopes.

Carbon has several isotopes, including Carbon-12, Carbon-13, and Carbon-14, which differ in their number of neutrons.
The atomic mass of carbon is the weighted average of the masses of its isotopes.

Some isotopes are radioactive, meaning their nuclei are unstable and break down at a constant rate over time.
Radioactive isotopes can be used to detect cancer, kill bacteria, and label substances in the body.

A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.
Chemical compounds have physical and chemical properties that are usually different from those of the elements they are composed of.
Chemical formulas, such as H2O for water and NaCl for table salt, show the composition of compounds.

Chemical bonds are formed when atoms are rearranged to hold together.
The main types of chemical bonds are ionic bonds and covalent bonds.
Ionic bonds are formed when one or more electrons are transferred from one atom to another, resulting in the formation of ions with opposite charges.
Covalent bonds are formed when electrons are shared between atoms, resulting in a molecule.

Ionic bonds are formed when atoms gain or lose electrons to achieve a stable number of electrons.
Positively and negatively charged ions are attracted to each other, forming an ionic bond.

Covalent bonds are formed when electrons are shared between atoms.
The moving electrons travel about the nuclei of both atoms, forming a covalent bond.
When atoms share one electron, a single covalent bond is formed, and when they share four electrons, a double bond is formed.

Weak interactions, such as van der Waals forces and hydrogen bonds, play important roles in the chemistry of living things.
Van der Waals forces are the attraction between molecules, and they can be strong enough to hold molecules together.
Hydrogen bonds are essential to understanding the special properties of water.