Chem 2 Grade 9

Stoichiometric relationships

Describe the quantitative ratios of reactants and products in a chemical reaction, based on balanced chemical equations.

Importance of stoichiometry

Allows scientists to calculate exact amounts of substances needed or produced, preventing waste and ensuring reactions occur efficiently.

Mole

A counting unit that allows chemists to measure atoms and molecules by mass, since they are too small to count individually.

How stoichiometric relationships relate to the mole

Balanced equations give ratios in moles, allowing scientists to quantify proportions of substances involved in reactions.

Law of conservation of mass

Mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

Conservation of mass in chemical reactions

Atoms are rearranged, not created or destroyed, so the total number of each type of atom remains constant.

Application of conservation of mass to chemical equations

The number of each type of atom must be the same on both sides of the equation.

Skill needed to apply conservation of mass

Students must construct and balance chemical equations.

Balancing a chemical equation

Adjusting coefficients so that the number of atoms of each element is equal on both sides.

Use of coefficients instead of changing formulas

Changing formulas changes the substance itself; coefficients only change quantity.

State symbols

Show the physical state of substances, providing extra information about the reaction.

Representation of state symbols

(s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).

Electrostatic attraction

The force of attraction between oppositely charged particles.

Fundamentals of electrostatic attraction to bonding

It is the force that holds particles together, forming bonds and structures.

Creation of structures through electrostatic attraction

Attractions act in all directions, producing regular arrangements such as lattices.

Bonding influence on physical properties

The strength and type of attraction between particles affects melting point, conductivity, and solubility.

Ionic bond

A strong electrostatic attraction between oppositely charged ions.

Formation of ionic bonds

Through the transfer of electrons from a metal to a non-metal.

Reason for electron transfer in ionic bonding

Atoms gain stable electron configurations by filling or emptying their outer shells.

Structure of ionic compounds

A giant ionic lattice.

Giant ionic lattice

A regular, repeating three-dimensional arrangement of positive and negative ions.

Strength of ionic lattices

Each ion is attracted to many oppositely charged ions in all directions.

High melting points of ionic compounds

Large amounts of energy are required to overcome strong electrostatic attractions throughout the lattice.

Brittleness of ionic compounds

When layers shift, like charges align and repel, causing the lattice to fracture.

Conductivity of ionic compounds when molten or aqueous

Ions are free to move and carry charge.

Conductivity of solid ionic compounds

Ions are fixed in place and cannot move.

Metallic bonding

Electrostatic attraction between positive metal ions and delocalized electrons.

Delocalized electrons

Electrons that are not attached to a single atom and can move freely through the lattice.

Structure of metals

A lattice of positive ions surrounded by a sea of delocalized electrons.

Electrical conductivity of metals

Delocalized electrons move and carry charge.

Heat conductivity in metals

Electrons transfer kinetic energy rapidly through the lattice.

Malleability of metals

Layers of ions can slide while metallic bonding remains intact.

Ductility of metals

The lattice can deform without breaking bonds.

Covalent bond

A strong electrostatic attraction between nuclei and shared electron pairs.

Reason for covalent bond formation

Non-metal atoms share electrons to achieve stable outer shells.

Atoms that form covalent bonds

Non-metal atoms.

Simple molecule

A small, distinct group of atoms held together by covalent bonds.

Low melting points of simple covalent substances

Only weak intermolecular forces are overcome when melting.

Electric conductivity in simple covalent substances

They have no free ions or delocalized electrons.

Influence of bonding type on melting point

Stronger attractions and larger structures lead to higher melting points.

Higher melting points of ionic substances compared to covalent substances

Ionic lattices contain strong attractions throughout the structure.

Bonding effect on solubility

Solubility depends on the attraction between particles and the solvent.

Conductivity link to structure

Conductivity requires mobile charged particles.

Altering physical properties of a substance

By changing its structure or composition.

Alloy

A mixture of metals, or a metal with a non-metal.

Hardness of alloys compared to pure metals

Different-sized atoms disrupt the lattice and prevent layers from sliding.

Effect of alloy composition on properties

Changing proportions alters strength, hardness, and durability.

Giant covalent structure

A large network of atoms bonded by strong covalent bonds.

High melting points of giant covalent substances

Many strong covalent bonds must be broken.

Property influence of diamond structure

Each atom forms four bonds, making it extremely hard.

Property influence of graphite structure

Layered structure allows sliding and electrical conductivity.

Intermolecular forces

Forces of attraction between molecules.

Effect of intermolecular forces on melting and boiling points

Stronger attractions require more energy to separate molecules.

Relevance of specific types of intermolecular forces

Only the effect, not classification, is needed at this level.

Polymer

A large molecule made from many repeating monomers.

Monomer

A small molecule that joins with others to form a polymer.

How polymer structure affects properties

Chain length and bonding determine strength and flexibility.

Cross-linking in polymers

Links between polymer chains.

Effect of cross-linking on polymer properties

It increases rigidity and strength.

Changing polymer properties for sustainability

By altering chain length, adding plasticisers, or increasing recycling.

Lattice in ionic substances

A regular, repeating three-dimensional arrangement of oppositely charged ions held together by strong electrostatic attractions.

Why are lattices three-dimensional?

Electrostatic attractions act in all directions, not just in one plane.

Atom

The smallest particle of an element that still retains the chemical properties of that element.

Why is an atom electrically neutral?

It has equal numbers of protons and electrons.

Ion

A charged particle formed when an atom gains or loses electrons.

Effect of losing electrons on an atom

It becomes a positive ion (cation).

Effect of gaining electrons on an atom

It becomes a negative ion (anion).

Another simple molecule definition

A small group of atoms joined by covalent bonds, usually with low melting points.

Why are simple molecules small?

They consist of a limited number of atoms bonded together.

Another giant covalent structure definition

A massive network of atoms bonded by strong covalent bonds throughout the structure.

Why are giant covalent structures solids?

The strong covalent bonds hold atoms firmly in place.

Allotrope

Different structural forms of the same element.

Why do allotropes have different properties?

Their atoms are arranged and bonded differently.

What is polymerisation?

The chemical process where monomers join to form polymers.

How does cross-linking affect flexibility?

It reduces flexibility by restricting movement of chains.

Why does cross-linking increase strength?

Chains are locked together, making the structure more rigid.

Why is electrostatic attraction strong in ionic bonds?

Because it acts between fully charged ions.

Definition of an intermolecular force

A force of attraction between molecules, not within them.

Why are intermolecular forces weaker than covalent bonds?

They involve partial attractions rather than shared electrons.

Electrical conductor definition

A substance through which charged particles can move.

Why are metals good electrical conductors?

They contain delocalised electrons.

Physical property definition

A characteristic observed without changing the substance’s identity.

Examples of physical properties

Melting point, conductivity, hardness, solubility.

Chemical property definition

A substance’s ability to react and form new substances.

Why is flammability a chemical property?

It involves a chemical reaction (combustion).

Melting definition

A physical change from solid to liquid.

Why is melting a physical change?

No new substance is formed.

Soluble definition

Able to dissolve in a solvent to form a solution.

Why are many ionic compounds soluble in water?

Water stabilizes ions by attraction.

Why do ionic compounds have high melting points?

Strong electrostatic attractions must be overcome throughout the lattice.

Why do simple covalent compounds have low melting points?

Only weak intermolecular forces are broken.

Why do giant covalent substances have very high melting points?

Strong covalent bonds must be broken across the entire structure.

Why do metals conduct electricity as solids?

Electrons are delocalised and mobile.

Why do ionic solids not conduct electricity?

Ions are fixed in place.

Why do molten ionic compounds conduct electricity?

Ions are free to move.

How does changing alloy composition change properties?

Different atom sizes disrupt lattice layers.

Why are alloys stronger than pure metals?

Irregular arrangements prevent easy sliding.

Why is graphite soft but diamond hard?

Graphite has layered bonding; diamond has a rigid 3D network.

Why does graphite conduct electricity?

It has delocalised electrons within layers.

Why does diamond not conduct electricity?

All electrons are used in covalent bonds.