Topic 2 - Chemistry

Chemistry and Water

What is Matter?

Definition: Matter is anything that has mass and takes up space.
States of Matter:
- Solid
- Liquid
- Gas
- Plasma
Phase Transitions:
- Freezing
- Condensation
- Deionization
- Melting
- Vaporization
- Ionization

Atomic Structure

Atom Components:
- Proton (p): Positively charged particle, located in the nucleus.
- Neutron (n): Neutrally charged particle, located in the nucleus.
- Electron (e): Negatively charged particle, orbits the nucleus in electron shells/orbits.
Nucleus: The central part of an atom containing protons and neutrons.

Elements and the Periodic Table

Element Representation:
- H (Hydrogen):
  - Atomic number: 1
  - Atomic weight: 1.00784
  - Protons: 1
  - Neutrons: 0
- O (Oxygen):
  - Atomic number: 8
  - Atomic weight: 15.999
  - Protons: 8
  - Neutrons: 8
- C (Carbon):
  - Atomic weight: 12.011
  - Protons: 6
  - Neutrons: 6
- Na (Sodium):
  - Atomic number: 11
  - Atomic weight: 22.98976928
  - Protons: 11
  - Neutrons: 12
- Ag (Silver):
  - Atomic number: 47
  - Atomic weight: 107.87
  - Protons: 47
  - Neutrons: 61
- Pb (Lead):
  - Atomic number: 82
  - Atomic weight: 207.2
  - Protons: 82
  - Neutrons: 126
Periodic Table Information per Element:
- Atomic Number: Number of protons (top left).
- Symbol: Abbreviation of the element's name (center).
- Name: Full name of the element (below symbol).
- Atomic Weight: Average mass of an atom of the element (below name).
- Electrons per shell: Distribution of electrons in different energy levels (bottom numbers).
Classification (Color Coding):
- State of matter: Gas, Liquid, Solid, Unknown.
- Subcategory: Alkali metals, Alkaline earth metals, Transition metals, Lanthanides, Actinides, Post-transition metals, Metalloids, Reactive nonmetals, Noble gases, Unknown chemical properties.

Ions and Isotopes

Ion: An atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge.
- Hydrogen atom (H):
  - Protons: 1
  - Neutrons: 0
  - Electrons: 1
  - Charge: Neutral
  - Mass: 1
- Hydrogen ion (H^{+1}):
  - Protons: 1
  - Neutrons: 0
  - Electrons: 0
  - Charge: +1
  - Mass: 1
- Carbon atom (C):
  - Protons: 6
  - Neutrons: 6
  - Electrons: 6
  - Charge: Neutral
  - Mass: 12
- Carbon ion (C^{-2}):
  - Protons: 6
  - Neutrons: 6
  - Electrons: 8
  - Charge: -2
  - Mass: 12
Isotope: Atoms of the same element (same number of protons) that have different numbers of neutrons, and therefore different atomic masses.
- Hydrogen-2 (Deuterium) isotope:
  - Protons: 1
  - Neutrons: 1
  - Electrons: 1
  - Charge: Neutral
  - Mass: 2
- Carbon-14 isotope:
  - Protons: 6
  - Neutrons: 8
  - Electrons: 6
  - Charge: Neutral
  - Mass: 14

Chemical Bonds

Definition: Interactions of electrons between different atoms that create stable molecules.
Types of Chemical Bonds:
- Ionic Bond:
  - Mechanism: Occurs when one atom loses electron(s) and another atom gains these electrons. This transfer creates ions with opposite charges (cations and anions).
  - Attraction: The resultant positive and negative ions are attracted to each other due to electrostatic forces.
  - Example: Sodium Chloride (NaCl)
    - Sodium (Na) has 1 outer shell electron; it loses it to become Na^{+1}.
    - Chlorine (Cl) has 7 outer shell electrons (needs 8 for stability); it gains 1 electron to become Cl^{-1}.
    - Na^{+1} and Cl^{-1} are attracted to form NaCl.
- Covalent Bond:
  - Mechanism: Electrons are shared between two atoms, orbiting both nuclei.
  - Example: Water (H_2O)
    - Hydrogen (H) needs 2 outer shell electrons, has 1.
    - Oxygen (O) needs 8 outer shell electrons, has 6.
    - Two H atoms each share an electron with the O atom, forming O-H bonds.

Polarity in Covalent Bonds

Nonpolar Covalent Bond:
- Mechanism: Electrons are shared equally between two atoms.
- Result: The molecule has no partial charges and is electrically neutral.
- Examples: Nitrogen gas (N2), Chlorine gas (Cl2), Carbon Dioxide (O=C=O).
Polar Covalent Bond:
- Mechanism: Electrons are shared unequally between two atoms due to differences in electronegativity.
- Result: Creates slight positive ( ext{δ}+) and slight negative ( ext{δ}-) ends or regions within the molecule.
- Examples: Hydrogen Chloride (H^{ ext{δ}+}-Cl^{ ext{δ}-}), Water (H_2O - Oxygen is ext{δ}- while Hydrogens are ext{δ}+).

Hydrogen Bonds

Definition: An intermolecular attraction between two molecules (not an intramolecular bond).
Mechanism: Occurs between the slightly positive hydrogen atom ( ext{δ}+) of one polar molecule and a slightly negative atom (typically Oxygen, Nitrogen, or Fluorine) of another polar molecule.
Result: This attraction makes molecules 'sticky' to each other.
Example: Water molecules form hydrogen bonds with other water molecules.

Chemical Formulas and Structures

Water:
- Chemical formula: H_2O
- Structure: H-O-H
Carbon Dioxide:
- Chemical formula: CO_2
- Structure: O=C=O
Methane:
- Chemical formula: CH_4
- Structure: H-C(H_3)
Ethanol:
- Chemical formula: C2H5OH
- Structure: H3C-CH2-OH

Properties of Water

Universal Solvent:
- Definition: Water's ability to dissolve many substances due to its polar nature.
- Mechanism: The ext{δ}- oxygen end of water molecules is attracted to positive ions, and the ext{δ}+ hydrogen ends are attracted to negative ions. This forms hydration shells around solute particles, separating them and dissolving the substance.
- Example: Dissolving Salt Crystals (NaCl) in water, where Na^+ ions are surrounded by water's oxygen ends and Cl^- ions are surrounded by water's hydrogen ends.
- Non-mixing substances: Substances that are nonpolar (e.g., oil) will not mix with water.
Solution Components:
- Solute: The substance that is being dissolved.
- Solvent: The substance that does the dissolving.
- Solution: The homogeneous mixture formed when a solute dissolves in a solvent.
Density of Water:
- Ice: Less dense than liquid water because its hydrogen bonds form a stable, ordered, crystalline lattice structure that holds molecules further apart.
- Liquid Water: Denser than ice because hydrogen bonds constantly break and re-form, allowing molecules to pack more closely together.
- Order of density (most to least): Liquid water > Ice > Water vapor.
High Heat Capacity:
- Definition: Water has a high specific heat capacity (4200 J/kg^ ext{°}C).
- Meaning: It requires a significant amount of energy to raise or lower its temperature. Water warms up and cools down slowly.
- Comparison:
  - Copper: 390 J/kg^ ext{°}C (warms/cools quickly).
  - Aluminum: 910 J/kg^ ext{°}C (warms/cools quickly).
- Impact on Ecosystems: Large bodies of water moderate temperature fluctuations in surrounding environments, creating stable habitats crucial for life. This prevents extreme thermal changes. Ground heats up faster than water due to its lower specific heat capacity.

Hydrophilic and Hydrophobic Substances

Hydrophilic:
- Attracted to water.
- Includes polar and charged molecules.
Hydrophobic:
- Repelled by water.
- Includes nonpolar molecules (e.g., oil).

Practice Questions/Review Concepts

Weakest Chemical Bond: Hydrogen bonds are generally the weakest among ionic, covalent, and hydrogen bonds.
Polar vs. Nonpolar Covalent Bonds: Polar bonds involve unequal sharing of electrons, leading to partial charges; nonpolar bonds involve equal sharing of electrons, resulting in neutral molecules.
Why Water is 'Sticky': Due to the formation of hydrogen bonds between water molecules.
Hydrogen Bonds and Nonpolar Molecules: Hydrogen bonds are not possible between nonpolar molecules because they lack the necessary partial charges.
Ionic Bond Example: Magnesium losing two electrons and oxygen gaining them forms an ionic bond.
Covalent Bond Example: Nitrogen gas forming when three pairs of electrons orbit both atoms is a covalent bond.