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Definition of Matter

Matter is anything that takes up space and has mass, including organisms, rocks, oceans, and air. All matter consists of at least one chemical.

• Chemical Elements: Pure substances made of only one type of atom.

• Atoms: The smallest unit of an element and the smallest unit of matter.

Example: Atoms are the smallest units of matter, as seen in substances like diamond (carbon atoms) and honey (glucose molecules).

Atomic Structure

Subatomic Particles

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

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

Elements of Life

Essential Elements

Of all the known elements, only a small subset is found in living organisms. The periodic table arranges all known elements based on their chemical properties.

• CHNOPS: 97% of the mass of most life is composed of Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur.

• Trace Elements: Elements required for life in small amounts.

Atomic Properties

Atomic Number and Mass Number

Each atom of an element has unique properties:

• Atomic Number (Z): Number of protons in the nucleus (characteristic of each element).

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

• Atomic Mass: Weighted average mass of all atoms of an element.

Formula:

Example: Atomic properties of a carbon atom: 6 protons, 6 neutrons, atomic number 6, mass number 12.

Electron Orbitals and Energy Shells

Electron Arrangement

Electrons are arranged in 3D regions around a nucleus called energy shells or orbitals.

• Shells closer to the nucleus are lower in energy than shells farther away, which are higher in energy.

• Valence Electrons: Electrons found in the outermost energy shell.

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

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

Octet Rule

Stability of Atoms

Atoms are more stable (less reactive) when their valence shells are fully occupied. This is known as the octet rule.

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

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

Example: Neon (atomic number 10) is unreactive because its valence shell is full with 8 electrons.

Isotopes

Definition and Properties

All atoms of an element have the same number of protons, but not necessarily the same number of neutrons. Isotopes are atoms of the same element that vary in the number of neutrons.

• Atomic Number: Number of protons

• Mass Number: Number of protons plus neutrons

• Atomic Mass: Weighted average of all isotopes

Example: Atomic mass of carbon is a weighted average of its isotopes.

Radioactive Isotopes

Radioactivity and Half-Life

Radioactive isotopes are unstable and break down, emitting energy in the form of rays or particles.

• Half-Life: Time it takes for half of all radioactive atoms in a sample to break down.

• Radioactive isotopes are used in medicine and radioactive dating of fossils.

Formula:

Example: Carbon-14 has a half-life of 5,730 years and is used for dating fossils.

Practice Questions and Applications

Sample Questions

• What is the atomic number of an element equal to?

• How many neutrons are in an oxygen atom with a mass number of 16 and atomic number of 8?

• How many valence electrons does an atom with five total electrons have?

• What is true about electron energy shells?

• How are isotopes of carbon and nitrogen different?

• How is radioactive dating used in science?

Example: The isotope Carbon-14 is used to date fossils and has a half-life of 5,730 years.

Additional info: These notes cover foundational topics in general chemistry, including atomic structure, elements, isotopes, and radioactivity, with relevant examples and practice questions for exam preparation.