Atoms, Elements, and Compounds: Comprehensive Study Guide

Fundamentals of Atomic Theory and Elements

• Definition of an Atom: The smallest part of an element that retains the chemical properties of that element.

• Atomic Structure:     - Nucleus: A tiny, dense central core containing protons and neutrons.     - Protons: Subatomic particles with a positive charge ($+$).     - Neutrons: Subatomic particles with no charge (neutral).     - Electrons: Negatively charged particles ($-$) that form a cloud and spin around the nucleus.

• Definition of an Element: A substance that cannot be broken down into anything simpler by chemical means.     - There are $90$ naturally occurring elements.     - Elements are categorized into metals and non-metals ($20$ are non-metals, while the remainder are metals).

• Properties of Metals:     1. Malleable: They can be hammered down into thin sheets.     2. Ductile: They can be drawn or stretched into wire.     3. Sonorous: They produce a ringing sound when struck.     4. Lustre: They appear shiny when polished.     5. Conductivity: They are good conductors of both heat and electricity.     6. Melting Point: Generally possess high melting points.

• Properties of Non-Metals:     1. Brittle: They break or shatter easily.     2. Conductivity: They are poor conductors of heat and electricity.     3. Appearance: They appear dull.     4. Melting Point: Generally possess low melting points.

Chemical Symbols and the Periodic Table

• Symbolism: Every element is allocated a symbol. The first letter is always a capital letter. Symbols often derive from Latin names (e.g., Sodium is $\text{Na}$ from Natrium).

• Comprehensive List of Elements and Symbols:     - Hydrogen: $\text{H}$ (Atomic Number: $1$)     - Helium: $\text{He}$ (Atomic Number: $2$)     - Lithium: $\text{Li}$ (Atomic Number: $3$)     - Beryllium: $\text{Be}$ (Atomic Number: $4$)     - Boron: $\text{B}$ (Atomic Number: $5$)     - Carbon: $\text{C}$ (Atomic Number: $6$)     - Nitrogen: $\text{N}$ (Atomic Number: $7$)     - Oxygen: $\text{O}$ (Atomic Number: $8$)     - Fluorine: $\text{F}$ (Atomic Number: $9$)     - Neon: $\text{Ne}$ (Atomic Number: $10$)     - Sodium: $\text{Na}$ (Atomic Number: $11$)     - Magnesium: $\text{Mg}$ (Atomic Number: $12$)     - Aluminium: $\text{Al}$ (Atomic Number: $13$)     - Silicon: $\text{Si}$ (Atomic Number: $14$)     - Phosphorous: $\text{P}$ (Atomic Number: $15$)     - Sulphur: $\text{S}$ (Atomic Number: $16$)     - Chlorine: $\text{Cl}$ (Atomic Number: $17$)     - Argon: $\text{Ar}$ (Atomic Number: $18$)     - Potassium: $\text{K}$ (Atomic Number: $19$)     - Calcium: $\text{Ca}$ (Atomic Number: $20$)     - Chromium: $\text{Cr}$ (Atomic Number: $24$)     - Manganese: $\text{Mn}$ (Atomic Number: $25$)     - Iron: $\text{Fe}$ (Atomic Number: $26$)     - Cobalt: $\text{Co}$ (Atomic Number: $27$)     - Nickel: $\text{Ni}$ (Atomic Number: $28$)     - Copper: $\text{Cu}$ (Atomic Number: $29$)     - Zinc: $\text{Zn}$ (Atomic Number: $30$)     - Bromine: $\text{Br}$ (Atomic Number: $35$)     - Silver: $\text{Ag}$ (Atomic Number: $47$)     - Tin: $\text{Sn}$ (Atomic Number: $50$)     - Iodine: $\text{I}$ (Atomic Number: $53$)     - Xenon: $\text{Xe}$ (Atomic Number: $54$)     - Barium: $\text{Ba}$ (Atomic Number: $56$)     - Tungsten: $\text{W}$ (Atomic Number: $74$)     - Platinum: $\text{Pt}$ (Atomic Number: $78$)     - Gold: $\text{Au}$ (Atomic Number: $79$)     - Mercury: $\text{Hg}$ (Atomic Number: $80$)     - Lead: $\text{Pb}$ (Atomic Number: $82$)

Compounds, Valency, and Formulae

• Definition of a Compound: A substance made up of two or more elements chemically combined. Elements in a compound are chemically joined and have a definite composition that cannot be varied.

• Examples of Common Compounds:     - Water ($H_{2}O$): Contains 2 elements and 3 atoms.     - Alcohol / Ethanol ($C_{2}H_{5}OH$): Contains 3 elements and 9 atoms.     - Carbon Dioxide ($CO_{2}$): Contains 2 elements and 3 atoms.     - Glucose ($C_{6}H_{12}O_{6}$): Contains 3 elements and 24 atoms.

• Valencies and Bonding Numbers: Used to determine the formulae of simple compounds. Many valencies correspond to the element's position on the periodic table (e.g., Many $+1$ valency elements are in Group 1).     - Positive Valencies:         - +1: Sodium ($Na$), Potassium ($K$), Lithium ($Li$), Silver ($Ag$), Hydrogen ($H$), Copper(I) ($Cu$—selective).         - +2: Copper(II) ($Cu$), Calcium ($Ca$), Magnesium ($Mg$), Zinc ($Zn$), Lead ($Pb$), Mercury ($Hg$), Iron(II) ($Fe$).         - +3: Iron(III) ($Fe$), Aluminium ($Al$).         - +4: Tin ($Sn$).     - Negative Valencies:         - -1: Fluoride ($F$), Chloride ($Cl$), Bromide ($Br$), Iodide ($I$).         - -2: Sulphide ($S$), Oxide ($O$).         - -3: Nitride ($N$), Phosphide ($P$).

• Rules for Formula Writing:     - The positive and negative valencies must cancel out (sum up to zero).     - Example (Calcium Chloride): Calcium has a valency of $2+$ and Chloride has a valency of $1-$. To cancel, $2$ Chloride atoms are needed ($2 \times 1- = 2-$). Formula: $CaCl_{2}$.     - Roman Numerals: Used if a metal has more than one valency (e.g., Iron(II) Oxide). Symbols: $Fe^{2+}$ and $O^{2-}$; they cancel one-to-one. Formula: $FeO$.

Mixtures vs. Compounds

Types of Mixtures

• Pure Substance: Contains only one type of particle (e.g., Pure water contains only water molecules).

• Solution: One substance (solute) dissolves in another (solvent). Solute particles are molecules or ions.

• Alloy: A special solution where two or more metals are dissolved in each other (e.g., Brass ($Zn/Cu$), Stainless steel).

• Suspension: Fine particles suspended in a liquid or gas. These particles are insoluble and may settle out as sediment if left undisturbed.     - Colloid: A suspension where particles do not settle out.     - Examples: Smoke (ash in air), Muddy water, Fog or Mist.

• Emulsion: A mixture of two or more immiscible liquids where droplets of one are suspended in the other. Immiscible means completely insoluble in one another (e.g., oil and water).     - Examples: Salad dressing (oil and vinegar), Butter (water in fat).

• Liquid Definitions:     - Solvent Distinction: If solute and solvent are in the same phase, the solvent is the one with the greater volume.     - Aqueous solution: A solution where the solvent is water.     - Miscible: Liquids that are completely soluble in one another (e.g., water and alcohol).

• The Case of Milk: Milk is a complex mixture being a solution (sugar in water), a suspension (protein bits in water), and an emulsion (fat droplets in water).

Separating Suspensions

• Filtration: Uses a filter (e.g., filter paper) to separate an insoluble solid from a fluid.     - Residue: The solid that does not pass through the filter.     - Filtrate: The fluid that passes through the filter.     - Examples:         - Filtering smoke: Residue is ash, filtrate is air.         - Filtering muddy water: Residue is sand, filtrate is water.

• Centrifuge: Separates mixtures by spinning them rapidly (up to $150,000\,rpm$). The denser substance is thrown outward to the base.     - Example: In milk, less dense cream ends up on top and can be skimmed off to produce "skimmed milk."

Separating Emulsions and Miscible Liquids

• Separating Funnel: Used for emulsions that separate on standing due to different densities (e.g., kerosene oil and water). The denser liquid is run out of the stopcock first.

• Fractional Distillation: Separates two or more miscible liquids with different boiling points.     - Process: The solution is boiled; vapour passes through a fractionating column (often packed with glass beads). The more volatile liquid reaches the top first and is condensed using a Liebig Condenser.     - Example: Separating crude oil into petrol, diesel, paraffin, oil, and tar.

Separating Solutions

• Evaporation: Used if only the solid solute is required. The solvent is evaporated using a Bunsen burner or a steam bath.     - Steam Bath usage: Required when the solute may break down if heated strongly (e.g., sugar) or the solvent is flammable (e.g., alcohol).

• Crystallisation: The solution is boiled to concentrate it, then cooled. Crystals form and are filtered off.

• Distillation: Used to collect the solvent from the solution. The solution is boiled, and vapour is condensed to liquid via a Liebig Condenser.     - Example: Distilling fresh water from sea water.

Other Separation Techniques

• Chromatography: Separates various dyes in ink by running the ink along filter paper using a solvent. Different dyes run at different rates.     - Identification: Chromatography identifies dyes because the same dye in different samples will run the same distance under identical conditions.

• Magnets: Separates magnetic substances (like iron) from other substances (e.g., iron and sulphur).

• Screening (Sieve): Separates different sized particles (e.g., flour and rice).

• Hand Separation: Used for large particles that can be picked apart by hand.

Fundamentals of Atomic Theory and Elements

• Definition of an Atom: The smallest part of an element that retains the chemical properties of that element.

• Atomic Structure:

  • Nucleus: A tiny, dense central core containing protons and neutrons.

  • Protons: Subatomic particles with a positive charge ($+$).

  • Neutrons: Subatomic particles with no charge (neutral).

  • Electrons: Negatively charged particles ($-$) that form a cloud and spin around the nucleus.

• Definition of an Element: A substance that cannot be broken down into anything simpler by chemical means.

• There are $90$ naturally occurring elements.

• Elements are categorized into metals and non-metals ($20$ are non-metals, while the remainder are metals).

• Properties of Metals:

  1. Malleable: They can be hammered down into thin sheets.

  2. Ductile: They can be drawn or stretched into wire.

  3. Sonorous: They produce a ringing sound when struck.

  4. Lustre: They appear shiny when polished.

  5. Conductivity: They are good conductors of both heat and electricity.

  6. Melting Point: Generally possess high melting points.

• Properties of Non-Metals:

  1. Brittle: They break or shatter easily.

  2. Conductivity: They are poor conductors of heat and electricity.

  3. Appearance: They appear dull.

  4. Melting Point: Generally possess low melting points.