Introduction to Matter and Chemical Elements

Definition of Matter

Matter is anything that takes up space and has mass. All living and non-living things are composed of matter, including organisms, rocks, oceans, and air.

• All matter consists of at least one chemical.

Chemical Elements

Chemical elements are pure substances made of only one type of atom. Each element is defined by its unique atomic structure.

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

• Atoms make up both elements and compounds.

Example: Atoms are the smallest units of matter, as seen in the structure of diamonds (carbon atoms) and glucose (carbon, hydrogen, and oxygen atoms).

Atomic Structure

Subatomic Particles

Atoms are made of subatomic particles, each with a characteristic charge, mass, and location within the atom.

Example: Negatively charged particles of atoms with almost no mass are called electrons.

Elements of Life

Essential Elements

Of all known elements, only a small subset is found in living organisms. The Periodic Table of Elements arranges all known elements based on their chemical properties.

• Approximately 97% of the mass of most life is composed of Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), and Sulfur (S) (CHNOPS).

• Other elements, called trace elements, are required for life in small amounts.

Example: The periodic table highlights the essential and trace elements for life.

Atomic Properties

Atomic Number and Mass Number

Each atom of an element has unique properties:

• Atomic number (Z): Number of protons in the nucleus (defines the element).

• Mass number (A): Total number of protons and neutrons in the nucleus.

• Atomic mass: The average mass of all atoms of an element (measured in atomic mass units, amu).

Example: A carbon atom has 6 protons (atomic number 6) and typically 6 neutrons (mass number 12).

Electron Orbitals and Energy Shells

Electron Arrangement

Electrons are arranged in shells (energy levels) around the nucleus. Shells closer to the nucleus are lower in energy, while those farther away are higher in energy.

• Valence electrons: Electrons found in the outermost energy shell; these determine chemical reactivity.

• The first shell holds up to 2 electrons; the second shell holds up to 8 electrons.

Example: The energy shells for C, H, N, O, P, and S show the distribution of electrons in each shell.

Octet Rule

Stability of Atoms

The octet rule states that atoms are more stable (less reactive) when their valence shells are fully occupied, typically with 8 electrons.

• Atoms are reactive when their outer valence shells are not full.

• First energy shell holds up to 2 electrons; second energy shell holds up to 8 electrons.

Example: Nitrogen (atomic number 7) has an electron distribution of 2 in the first shell and 5 in the second shell.

Isotopes and Atomic Mass

Definition of Isotopes

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

• Atomic number (Z): Number of protons (same for all isotopes of an element).

• Mass number (A): Number of protons plus neutrons (varies among isotopes).

• Atomic mass: The weighted average of all isotopes of an element.

Example: Carbon-12, Carbon-13, and Carbon-14 are isotopes of carbon with different numbers of neutrons.

Radioactive Isotopes

Definition and Applications

Radioactive isotopes are unstable isotopes that break down and emit energy in the form of rays or particles. The half-life is the time it takes for half of a sample of radioactive atoms to decay.

• Radioactive isotopes are used in medicine, archaeology (dating fossils), and biological research.

• They can be used to trace the movement of substances in organisms or to treat diseases such as cancer.

Example: Carbon-14 is a radioactive isotope used in radiocarbon dating. It has a half-life of 5,730 years.

Key Formulas and Equations

• Atomic Number:

• Mass Number:

• Number of Neutrons:

• Average Atomic Mass:

• Half-Life Decay:

Summary Table: Subatomic Particles

Additional info:

• Valence electrons are crucial for chemical bonding and reactivity.

• Radioactive decay follows first-order kinetics, and the half-life is a constant for each isotope.