Chemistry: Elements, Compounds, and Mixtures

Defining Elements, Compounds, and Mixtures

• Element: A pure substance that cannot be broken down into simpler substances by chemical means. Examples include hydrogen (H), oxygen (O), and gold (Au).
• Compound: A substance formed by the chemical combination of two or more different elements in a fixed ratio. Examples include water (H₂O), carbon dioxide (CO₂), and sodium chloride (NaCl).
• Mixture: A combination of two or more substances that are not chemically bonded and can be separated by physical means. Examples include air, saltwater, and a mixture of sand and water.

Chemical Formulas and Element Information

• SO₂: This formula indicates a compound containing one sulfur atom and two oxygen atoms.

Element Symbols

• Antimony: Sb
• Gold: Au
• Iron: Fe
• Mercury: Hg
• Potassium: K
• Silver: Ag
• Tin: Sn
• Tungsten: W

Element Names from Symbols

• Na: Sodium
• Mg: Magnesium
• Al: Aluminum
• Si: Silicon
• P: Phosphorus
• Ar: Argon

Symbol Pair Differences

• Co and Co (identical): Both represent the element cobalt, but one or two might represent different isotopes or different amounts of that certain element. Note: Need context or additional data for accurate interpretation.
• Cs and Cs (identical): Both represent the element cesium. Note: Same as above, context required for isotopes.
• Ho and H₂O: Ho represents the element Holmium, while H₂O represents water, a compound.
• 4P and P: 4P represents four phosphorus atoms; P represents one phosphorus atom.

Light Wavelengths

• Light wavelengths range from approximately 0.0000004 cm to 0.0000007 cm.
• In micrometers (µm): 0.4 µm to 0.7 µm
• In nanometers (nm): 400 nm to 700 nm

Significant Figures

• Determining the number of significant figures depends on the given numerical value, not the context.
• Significant figures rules are required for accurate counting of the data.

Scientific Notation Conversion

• 11.98: 1.198 × 10¹
• 0.0046940: 4.6940 × 10⁻³
• 4,679,000: 4.679 × 10⁶

Subatomic Particles

• Proton: Positively charged (+1)
• Neutron: No charge (0)
• Electron: Negatively charged (-1)

Atomic Symbols

• Atom with 24 protons, 24 electrons, and 28 neutrons: ⁴⁸Ti

Atomic Structure and Numbers

• Atom: Contains a nucleus with protons and neutrons, surrounded by electrons.
• Atomic number: Number of protons in an atom (e.g., 53).
• Mass number: Number of protons plus neutrons in an atom (e.g., 127).

More Atomic Symbols

• Atom with 34 protons, 45 neutrons, and 34 electrons: ¹⁷⁹Se

Polyatomic Ions

• Examples of polyatomic ions with -1, -2, and -3 charges:
  • Nitrate (NO₃⁻): -1 charge
  • Sulfate (SO₄²⁻): -2 charge
  • Phosphate (PO₄³⁻): -3 charge

Periodic Table

• Periods: Horizontal rows in the periodic table. Elements in the same period have increasing atomic numbers.
• Groups: Vertical columns in the periodic table. Elements in the same group have similar chemical properties.

Elements in the Same Group

• (b) Be, Mg, Ca: These elements are in the same group (Group 2).
• Need additional data for the other element sets.

Additional Element Data

• List of elements, and their symbols (H, He, Li, Be, B, C, N, O, F, Ne, ..., etc.)