The Nature of Matter and Atoms

The Nature of Matter

• 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.

Atoms

• 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

• 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

• 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.

Elements and Isotopes

• 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.

Isotopes of Carbon

• 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.

Radioactive 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.

Chemical Compounds

• 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

• 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

• 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

• 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

• 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.