Essential Chemistry Definitions and Concepts

Essential Chemistry Definitions

Fundamental Concepts

• Physical Property: Characteristics observed without changing the substance (color, melting point, density, boiling point).
• Chemical Property: Characteristics observed when a substance changes into another (reactivity with air, acid, base, water, other chemicals).
• Law of Conservation of Matter: Matter is neither created nor destroyed.
• Atomic Theory: Theory of the nature of atoms.
• Isotope: Atoms of the same element with different numbers of neutrons.
• Ion: Atom or molecule with a net electric charge.
• Cation: Positively charged ion.
• Anion: Negatively charged ion.
• Atomic Mass Unit (amu): Unit of mass for expressing atomic & molecular weights.
• Mole: Unit for amount of substance (6.022 x 10^23 particles).
• Molecule: Two or more atoms bonded together.
• Compound: Substance composed of two or more elements.
• Chemical Formula: Representation of a substance using symbols for its constituent elements.
• Percent Composition: Percent by mass of each element in a compound.
• Molecular Formula: Formula giving the number of atoms of each element in a molecule.

Key Scientists and Their Contributions

• John Dalton: Atomic theory.
• J.J. Thomson: Discovery of the electron.
• Ernest Rutherford: Nuclear model of the atom.
• Niels Bohr: Bohr model of the atom.
• Antoine Lavoisier: Law of Conservation of Mass.
• Dmitri Mendeleev: Periodic table.
• William Ramsay: Noble gases.
• Henry Moseley: Atomic number concept.
• Glenn Seaborg: Discovery of transuranium elements.
• Marie Curie: Radioactivity.
• Alexander Fleming: Discovery of penicillin.
• Dorothy Hodgkin: X-ray crystallography.
• Howard Florey & Ernst Chain: Development of penicillin.

Common Compounds

Examples of common compounds:

• NaCl: Sodium Chloride
• NO2: Nitrogen Dioxide
• CO2: Carbon Dioxide
• C6H12O6: Glucose
• C6H8O6: Vitamin C
• C14H18N2O5: Aspartame
• C16H17N2O4S (empirical): Penicillin
• NH3: Ammonia
• C19H29O2: Testosterone
• C18H22O2: Estradiol
• H2O: Water

Significant Figures

Rules for determining significant figures:

• All non-zero digits and any zeros contained between non-zero digits count (300042 - 6 sig figs).
• Leading zeros do not count (0.000034 - 2 sig figs).
• Trailing zeros count if there is a decimal point (0.0002500 - 4 sig figs).
• Trailing zeros may or may not count if there is no decimal point, so we go with the most conservative answer (190000 - 2 sig figs, could be 6).

Periodic Table Groups

• Alkali Metals (Group 1)
• Alkaline Earth Metals (Group 2)
• Transition Metals (Groups 3-12)
• Lanthanides (Elements 57-71)
• Actinides (Elements 89-103)
• Pnictogens (Group 15)
• Chalcogens (Group 16)
• Halogens (Group 17)
• Noble Gases (Group 18)

Diatomic molecules: Hydrogen, nitrogen, oxygen, fluorine, chlorine, iodine, bromine.

MF = Regular Molecular Formula, EF = Simplified Empirical Formula.

Metals, Nonmetals, and Metalloids

Metals

• Alkali Metals: Very reactive, not found freely in nature (sodium, potassium).
• Alkaline Earth Metals: Reactive, but less so than alkali metals (magnesium, calcium).
• Transition Metals: High melting points and densities, often form colored compounds (iron, copper).
• Lanthanides and Actinides: Rare earth elements, often radioactive (uranium, thorium).

Nonmetals

• Halogens: Very reactive, often form salts with metals (fluorine, chlorine).
• Noble Gases: Inert and non-reactive under normal conditions (helium, neon).

Metalloids

• Boron Group
• Nitrogen Group