CHEM 103 - UNIT 1

Element

The simplest type of matter that has unique properties and consists of only one type of atom

• ex) H, O, Na, Cl

Molecule

An independent structure made of at least two atoms bonded together by covalent bonds.

• ex) H₂, O₂, CH₄, H₂O

Compound

A substance formed when atoms of different element are chemically bonded together

• ex) NaCl, H₂O, NH₄Cl

Mixtures

Two or more substances physically combined but not chemically bonded

• ex) Air: 78% nitrogen (N₂) and 21% oxygen (O₂), 1% other gases

Proton (p⁺)

A positive charged subatomic particle with a mass of about 1 amu

• the atomic number

Neutron (n⁰)

A subatomic particle with no charge and a mass of about 1 amu

• ex) Carbon-12 has 6 neutrons, 6 protons

Electron

A negatively charged subatomic particle with very small mass

Atomic Number (Z)

The number of protons in an atom; defines the element.

• ex) Carbon Z = 6, carbon no matter what

Mass Number (A)

The total number of protons and neutrons in an atom

• Protons + Neutrons

• ex) Carbon-12 → 6 p⁺ + 6 n⁰ = 12

Atomic Symbol

The letters used to represent an element

• ex) Na = sodium, Cl = chlorine

Isotopes

Atoms of the same element with the same number of protons but different number of neutrons

• ex)

  • ³⁵Cl → (17 p⁺ + 18 n⁰)

  • ³⁷Cl → (17 p⁺ + 20 n⁰)

Ion

An atom that has gained or lost electrons and has a net charge

• ex) Na⁺, Cl^-

Cation

A positively charged ion formed by losing electrons

• ex) Na → Na⁺ + e^-

  • (A POSITIVE)

Anion

A negatively charged ion formed by gaining electrons

• ex) Cl + e^- → Cl^-

  • (A NEGATIVE)

Laws of Conservation of Mass

Mass is neither created nor destroyed in a chemical reaction

• Total mass of reactants = Total mass of products

Cathode Ray Experiment

Observation:

• Cathode rays bend toward positives plates and away from negative plates

Conclusion:

• Cathode rays are made of negative charged particles (electrons)

Result / Why it matters:

• Electrons EXIST! and are components of all atoms

Plum Pudding Model

Observation:

• Electrons were known to exist, but atomic mass was spread out

Conclusion:

• Atoms were thought to be area of positive charge with electrons embedded in them

Result / Why it matters:

• This model was later proven incorrect

Rutherford Gold Foil Experiment

Observation:

• Most alpha particles passed straight through the gold foil; some deflected/bounced back

Conclusion:

• Atoms are mostly empty space with a small, dense, positively charged nucleus

Result / Why it matters:

• This model was disproved by the nuclear atom model

Nuclear Atom Model

Observation:

• Alpha particle backscattering occurs only rarely.

Conclusion:

• Positive charge and most mass are concentrated in a tiny nucleus.

Result / Why it matters:

• Atoms consist of a nucleus surrounded by electrons.

Classical Mechanics

Motion of large, everyday objects

• Works for big things, not atoms

Quantum Mechanics

Electrons show wave-like behavior

• Successfully explains atoms and electrons