Chemistry Notes

What is a Pure Substance?

• Chemistry: Study of matter, its properties, and how it changes with energy transfer.
• Matter exists as:
  • Pure substances: Elements and compounds
  • Mixtures: Combinations of elements and compounds

Elements

• Most basic form of matter.
• Cannot be broken down by chemical or physical means.
• Mixtures can be separated physically (e.g., soda into syrup, sugar, and water).
• Currently, 118 identified elements.
• Everything in the universe is made up of these 118 elements.

Compounds

• Two or more elements chemically combined to form a new substance.
• Cannot be broken down physically but can be broken down chemically.
• Example: Water H_2O can be broken into oxygen and hydrogen.
• Orientation and specificity are crucial.
• Iron oxide vs. iron three oxide: different chemical properties despite same elements.

Chemical Formulas

• Water (H2O) vs. Hydrogen Peroxide (H2O_2).
• Adding one oxygen drastically changes chemical behavior.
• Importance of careful naming and identification of chemical formulas. A small difference can have significant consequences.

Chemical Abbreviations

• Instead of writing full chemical names, use one or two-letter abbreviations.
• Carbon: C
• Oxygen: O
• CO_2 is easier than writing "carbon, oxygen, oxygen."
• Be specific and careful when recording elements.
• Cobalt (Co) vs. Carbon Monoxide (CO): one is a metal for batteries, the other is a toxic gas.

Two Basic Types of Matter

• Elements and compounds are the two basic types of matter.

Atoms

• Elements are made of atoms.
• Atoms are the simplest, most stable form of an element.
• Analogy: Humans are all the same species, but each individual is unique.
• Atoms of the same element behave similarly but are not identical.
• Atoms consist of three subatomic particles and are located in two major regions:
  • Protons, neutrons, and electrons
  • Nucleus and electron cloud

Subatomic Particles

• Atoms are very tiny.
• Mass is measured in atomic mass units (amu).
• 1 amu = 1.6 \times 10^{-24} grams.

Protons

• Mass: 1 amu
• Charge: Positive (+1)
• Represented by: p
• Location: Nucleus

Neutrons

• Slightly bigger than protons, but considered roughly the same size.
• Neutral charge (no charge).
• Location: Nucleus

Electrons

• Considered massless.
• Location: Electron cloud (orbiting the nucleus).
• Charge: Negative (-1).

Table Summarizing Subatomic Particles

Power of an Atom

• Analogy: If a building is an atom, the nucleus is the size of a marker.
• All the mass is concentrated in the tiny nucleus.
• Life is made of tiny, dense, positive cores (nuclei) surrounded by massless negativity (electrons).

Periodic Table

• Elements are sorted based on similar properties.
• Vertical column: Group
• Horizontal row: Period

Properties of Elements

• Metals: Located on the left side of the periodic table.
  • Solid at room temperature (except mercury).
  • Hard substances.
  • Good conductors of heat and electricity.
  • Shiny.
• Nonmetals: Located on the right side of the periodic table.
  • Can be solids, liquids, or gases.
  • Lack luster.
  • Brittle if solid.
  • Poor conductors (good insulators).
• Metalloids: Touch the squiggly line on the periodic table.
  • Properties of both metals and nonmetals.
  • Varying conductivity.

Numbering of Groups and Periods

• Groups: Count from left to right (1, 2, 3, …).
• Periods: Count from top to bottom (1, 2, 3, …).
• Alternative Group Numbering:
  • Tall sections: Groups 1A, 2A, 3A (main elements).
  • Flat zone: B elements (rarer metals).

Isotopes and Atomic Number

• Atomic Symbol: Abbreviation of the element name.
• Atomic Number: Unique identifier for an element (like a Social Security number).
• Equals the number of protons in the nucleus.
• Changing the number of protons changes the element.
• Neutrons: Number can vary without changing the element.
• Isotopes: Atoms with the same number of protons but different numbers of neutrons.
• Mass Number: Total number of protons and neutrons in the nucleus.

Isotope Notation

• Chemical symbol with mass number in the upper left corner.
• Mass number = protons + neutrons.

Calculating Number of Neutrons

• Number of neutrons = mass number - atomic number.

Neutral Atoms

• In a neutral atom, the number of protons equals the number of electrons.

Atomic Masses

• Average number of all isotopes of every atom found in existence for a certain element. The value is shown with decimals on the periodic table.