Chemistry Study Material

Safety Hazard Symbols

All hazardous materials are required to display a label that features a hazard symbol. These symbols serve as a crucial visual guide to understanding the potential dangers associated with materials. Each hazard symbol conveys two key pieces of information: the shape of the symbol indicates the level of hazard present, while the symbol itself denotes the specific type of hazard involved.

WHMIS Symbols

The Workplace Hazardous Material Information System (WHMIS) encompasses a series of symbols designed to safeguard individuals who utilize materials that may pose hazards in the workplace environment. Familiarity with these symbols helps in recognizing the risks and implementing safe practices.

Physical Properties

Physical properties refer to characteristics of a substance that can be observed or measured without altering its composition. These properties are essential for identifying and categorizing materials. Key physical properties include:

Colour: The visual appearance of a material.
Lustre: The sheen or shine of a surface.
Hardness: Resistance to deformation or scratching.
Density: Mass per unit volume.
Conductivity: Ability to conduct electricity or heat.
Ductility: Ability to be drawn into wires.
Malleability: Ability to be hammered or pressed into shape.
Boiling Point: Temperature at which a substance transitions from liquid to gas.
Melting Point: Temperature at which a substance transitions from solid to liquid.
Crystal Shape: The geometric shape of a solid material.
Solubility: The ability to dissolve in a solvent.

Chemical Properties

Chemical properties describe how a substance interacts with other substances, illustrating its behavior during chemical reactions. Important chemical properties to understand include:

Reaction with Acids: Indicates the ability to neutralize acids.
Ability to Burn: Reflects the flammability of a substance.
Reaction with Water: Shows how a material behaves in the presence of water.
Behaviour in Air: Reveals stability or reactivity upon exposure to air.
Reaction to Heat: Indicates thermal stability and changes upon heating.

Changes in Matter

Physical Change

Physical changes are alterations that do not change the chemical composition of a substance. These changes are typically reversible, meaning the original form can be restored. Common examples of physical changes include:

Boiling water
Ripping paper
Melting ice cream

Chemical Change

In contrast, a chemical change involves a transformation in the substance's composition, yielding new substances with different properties. Chemical changes are generally irreversible. Indicators of a chemical change may include:

Production or absorption of heat
Consumption of starting materials
Change in colour
Odour production
Formation of a gas or solid (precipitate)
Irreversibility of the change

Organizing the Elements

The system of chemical symbols representing elements was proposed by the Swedish chemist Berzelius in 1814. The first letter (or two) of an element's name typically serves as its symbol. For example, hydrogen is denoted by H while helium is represented as He. Some elements utilize letters from their Latin names, such as Au for Gold and Pb for Lead. Today, elements may also be named after notable scientists or geographical locations.

Dmitri Mendeleev

Dmitri Mendeleev is credited with creating the first version of the periodic table in 1869. He systematically organized 63 elements according to their properties, placing those with similar chemical characteristics into “family groups.” Mendeleev's table included gaps for undiscovered elements, predicting their properties based on their positions. When these elements were later discovered, they exhibited the predicted traits, validating Mendeleev's model.

The Periodic Table

The periodic table is structured in horizontal rows called periods (numbered 1–7) and vertical columns known as groups or families (numbered 1–18). Elements within the same group possess similar chemical properties, reflecting their atomic structures.

Atomic Number & Mass

The atomic number of an element indicates the number of protons (and electrons) present in its atoms, which crucially determines the element's identity.

Metals and Non-metals

Metals

Metals exhibit several characteristic properties:

Shiny: They often possess a reflective surface.
Malleable: Metals can be hammered or shaped without breaking.
Ductile: They can be drawn into wires.
Solid at Room Temperature: With the exception of mercury (Hg), which is a liquid.
Conductors: Metals effectively conduct electricity and heat.

Non-metals

Non-metals, in contrast, may exist as solids or gases (with bromine as the only liquid non-metal). Their properties include:

Dull: They do not typically have a shiny or reflective surface.
Brittle: Non-metals tend to break or shatter easily.
Insulators: They do not conduct electricity or heat well, with the exception of carbon (C), which demonstrates some conductivity.

Metalloids

Metalloids exhibit properties that are intermediate between metals and non-metals.

Groups of Elements

Group 1 - Alkali Metals: Highly reactive, these metals react vigorously with air and water (excluding Hydrogen). Examples include Li, Na, K, Rb, Cs, and Fr.
Group 2 - Alkaline Earth Metals: Less reactive than alkali metals. Key examples are Be, Mg, Ca, Sr, Ba, and Ra.
Group 17 - Halogens: The most reactive non-metals, including F, Cl, Br, I, and At.
Group 18 - Noble Gases: These elements are known for their stability and lack of reactivity, which includes He, Ne, Ar, Kr, Xe, and Rn.

Formulas of Compounds

The chemical formula of a compound specifies the types of elements present and the number of each atom in the compound. For instance, H2O indicates two hydrogen atoms and one oxygen atom. No number specifies a singular atom count, such as one oxygen in H2O.

Ionic Compounds

Ionic compounds are formed between metals and non-metals through the transfer of electrons. Characteristics of ionic compounds include:

Effective electrical conductors
High melting and boiling points
Exist predominantly as solids at room temperature
Example: Sodium chloride (table salt) represented as NaCl.

Naming Ionic Compounds

The naming convention for ionic compounds dictates that the name of the metal precedes that of the non-metal, with the latter altered to end in 'ide.' For elements with multiple ionic charges, a Roman numeral indicates the specific charge. For example, Cu2O is named Copper (I) oxide.

Ionic Compound Formulas

The formulation process consists of several steps:

Write the symbol of the metal with its ionic charge, followed by that of the non-metal and its charge.
Balance the ionic charges as necessary.
Compile the final formula, indicating the number of atoms of each element.

Examples

Formulas can be derived from ionic charges as follows:

Ca⁺² and F^-1 combine to form CaF₂.
K⁺¹ and N^-3 combine to form K₃N.

Practice with these ionic compounds: ZnO, CaI₂, NaCl, MgCl₂, KBr, PbS₂.

Molecular Compounds

Molecular compounds form through the combination of non-metals, often existing as solids (such as sulfur), liquids (water), or gases (carbon dioxide). In molecular compounds, non-metal ions share electrons, resulting in covalent bonds. Features of molecular compounds include:

Lower melting and boiling points compared to ionic compounds
Poor conductors of electricity and heat

Naming Molecular Compounds

The first element retains its name, potentially incorporating a prefix (one through ten) if there are multiple atoms. The second element’s name changes to end with 'ide' and always includes a prefix for the number of atoms. For reference, the prefixes are:

1 - mono
2 - di
3 - tri
4 - tetra
5 - penta
6 - hexa
7 - hepta
8 - octa
9 - nona
10 - deca

Naming Examples

Some examples of molecular compounds include:

C₆H₈ - Tricarbon Octahydride
CCl₄ - Carbon Tetrachloride
CO₂ - Carbon Dioxide

Molecular Formula Examples

Additional examples include:

Tricarbon Tetraoxide
Silicon Dioxide
Tetraphosphorous Decaoxide
Triiodine Hexabromide

Super “7” (Diatomic Molecules)

Some elements exist naturally as diatomic molecules, particularly the Super “7”: N₂ (nitrogen), O₂ (oxygen), F₂ (fluorine), Cl₂ (chlorine), Br₂ (bromine), I₂ (iodine), H₂ (hydrogen).

Chemical Reactions

Chemical reactions occur when two or more substances interact to form one or more new substances. Indicators of a reaction include:

A noticeable colour change
The emergence of a new odour
The formation of a solid (precipitate) or gas
The release or absorption of heat

The original substances participating in the reaction are termed reactants, while the new substances produced are known as products.

Endothermic and Exothermic Reactions

Reactions can be classified based on thermal changes:

Endothermic Reactions: Absorb heat from the surroundings.
Exothermic Reactions: Release heat into the environment.

Chemical Reactions Involving Oxygen

Some common chemical reactions involving oxygen include:

Combustion: The reaction of oxygen with a substance, releasing energy, as seen in the equation CH₄ + O₂ → CO₂ + H₂O + heat.
Corrosion: Reaction of oxygen with a metal, such as Fe + O₂ + heat → FeO (rust).
Cellular Respiration: A vital chemical reaction in living cells that converts food and oxygen into energy: Food + Oxygen → Carbon Dioxide + Water + energy.

Conservation of Mass

The Law of Conservation of Mass establishes that in a chemical reaction, the total mass of the reactants equals the total mass of the products. This principle asserts that matter cannot be created or destroyed; it only changes form. Testing this law is feasible only in closed systems, wherein material cannot enter or exit. In open systems, such as beakers, gas or other materials may escape, creating a false appearance of mass loss among the products.

Rates of Reaction

Several factors influence the rate at which a chemical reaction occurs:

Presence of a catalyst, which accelerates the reaction.
Concentration of reactants, as higher levels typically promote more frequent interactions.
Temperature of the reactants, affecting molecular energy and reaction rates.
Surface area of the reactants, where increased surface area can enhance the speed of the reaction.

Comprehensive Chemistry Study Guide

Comprehensive Chemistry Study Guide