Chemistry Lecture Review

A mixture is a combination of two or more substances in which the substances retain their distinct identities.
Mixtures can be separated into their pure components by physical methods.
- Examples of physical separation means: distillation, magnets, strain (like straining pasta).
Types of Mixtures:
- Homogeneous mixture: The composition of the mixture is the same throughout.
  - Examples: soft drink, milk, solder.
- Heterogeneous mixture: The composition is not uniform throughout.
  - Examples: oil and water, cement, iron filings in sand.

A substance is a form of matter that has a definite composition and distinct properties.
- Examples: liquid nitrogen, gold ingots, silicone crystals.
Pure substances are classified into Elements and Compounds.

An element is a substance that cannot be separated into simpler substances by chemical means.
There are 117 elements that have been identified.
- 82 elements occur naturally on Earth (e.g., gold, aluminum, lead, oxygen, carbon, sulfur).
- 35 elements have been created by scientists (e.g., technetium, americium, seaborgium).
Table 1.1: Some Common Elements and Their Symbols
- Aluminum (Al), Arsenic (As), Barium (Ba), Bismuth (Bi), Bromine (Br), Calcium (Ca), Carbon (C), Chlorine (Cl), Chromium (Cr), Cobalt (Co), Copper (Cu).
- Fluorine (F), Gold (Au), Hydrogen (H), Iodine (I), Iron (Fe), Lead (Pb), Magnesium (Mg), Manganese (Mn), Mercury (Hg), Nickel (Ni), Nitrogen (N).
- Oxygen (O), Phosphorus (P), Platinum (Pt), Potassium (K), Silicon (Si), Silver (Ag), Sodium (Na), Sulfur (S), Tin (Sn), Tungsten (W), Zinc (Zn).

A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions.
Compounds can only be separated into their component elements by chemical means (e.g. fluoride, quartz, dry ice - carbon).

Physical change: A change that does not alter the composition or identity of a substance.
- Examples: Ice melting, sugar dissolving in water.
Chemical change: A change that alters the composition or identity of the substance involved.
- Example: Hydrogen burns in air to form water.

Mass: A measure of the quantity of matter.
- The SI unit of mass is the kilogram (kg).
- Conversion: 1 \text{ Kg} = 1000 \text{ g} = 1 \times 10^3 \text{ g}.
Weight: The force that gravity exerts on an object.
- Formula: \text{Weight} = c \times \text{mass}, where c is the acceleration due to gravity.
- Example: A 1 \text{ Kg} bar weighs 1 \text{ Kg} on Earth (where c \approx 1.0) but weighs 0.1 \text{ Kg} on the Moon (where c \approx 0.1).

An ion is an atom, or group of atoms, that has a net positive or negative charge.

An ion with a positive charge.
Formed when a neutral atom loses one or more electrons.
Example: A neutral sodium atom (Na) has 11 protons and 11 electrons. If it loses one electron, it becomes a sodium cation (Na^+}) with 11 protons and 10 electrons, resulting in a net +1 charge.

An ion with a negative charge.
Formed when a neutral atom gains one or more electrons.
Example: A neutral chlorine atom (Cl) has 17 protons and 17 electrons. If it gains one electron, it becomes a chloride anion (Cl^-$) with 17 protons and 18 electrons, resulting in a net -1 charge.

Monatomic ion: Contains only one atom.
- Examples: Na^+ , Cl^-, Ca^{2+}, O^{2-}, Al^{3+}, N^{3-}.
Polyatomic ion: Contains more than one atom.
- Examples: OH^- (hydroxide), CN^- (cyanide), NH4^+ (ammonium), NO3^- (nitrate).

NO2 - Nitrite

NO3 - Nitrate

OH^- - Hydroxide

NH4+ - Ammonium

PO4³- - Phosphate

CO3²- - Carbonate

SO3²- - Sulfite

SO4²- - Sulfate

C2H3O2 - Acetate

HCO3- - Hydrogen Carbonate (Bicarbonate)