Fundamentals of Atomic Structure and Elements in General Chemistry

Matter and Chemical Elements

Definition and Classification of Matter

Matter is anything that occupies space and has mass. All living and non-living things are composed of matter, which is made up of chemical elements.

• Matter: Anything that takes up space and has mass (e.g., organisms, rocks, oceans, air).

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

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

Example: Atoms are the smallest units of matter, forming substances like diamonds (carbon atoms) and honey (glucose molecules).

Atomic Structure

Subatomic Particles

Atoms are composed of subatomic particles, each with distinct charge, mass, and location within the atom.

Subatomic Particle	Electric Charge	Atomic Mass Unit (AMU)	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	-1	~0	Orbiting Nucleus

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

Practice: A proton is a positively charged subatomic particle found in the nucleus.

Elements of Life

Essential Elements for Living Organisms

Of all known elements, only a small subset is found in living organisms. The periodic table organizes elements by their chemical properties.

• CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur make up about 97% of the mass of most life forms.

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

Major Elements	Trace Elements
C, H, N, O, P, S	Fe, Zn, Cu, I, etc.

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

Atomic Properties

Atomic Number and Mass Number

Each atom of an element has unique properties, including atomic number and mass number.

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

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

• Atomic Mass: Average mass of all atoms of an element.

$\text{Atomic Number} = \text{Number of Protons}$ $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

Example: Carbon has an atomic number of 6 and a mass number of 12.

Electron Orbitals and Energy Shells

Electron Arrangement

Electrons are arranged in energy shells around the nucleus. These shells are regions where electrons are likely to be found.

• Shells closer to the nucleus are lower in energy; shells farther away 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.

Element	Atomic Number	Valence Electrons
Carbon	6	4
Hydrogen	1	1
Nitrogen	7	5
Oxygen	8	6
Phosphorus	15	5
Sulfur	16	6

Example: Carbon has 4 valence electrons in its outer 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.

• 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 is unreactive because its valence shell is full with 8 electrons.

Practice: Oxygen needs 2 more electrons to fulfill the octet rule in its valence shell.

Summary Table: Key Atomic Properties

Element	Atomic Number	Mass Number	Valence Electrons	Reactivity
Hydrogen	1	1	1	High
Carbon	6	12	4	Moderate
Oxygen	8	16	6	High
Neon	10	20	8	Low (inert)

Additional info: The notes include practice questions and diagrams to reinforce understanding of atomic structure, electron configuration, and the periodic table. These concepts are foundational for General Chemistry and are directly relevant to college-level coursework.