bonding t1

pure substance

matter with fixed composition and unique properties

characteristics of pure substances

fixed boiling + melting points

cannot be separated physically into simpler substances

types of pure substances

elements

compounds

elements

pure substance that cannot be chemically broken down into simpler substances

made of one type of atom

elements examples

metals: Au, Ag, Fe

non-metals: O₂, N₂, S

noble-gases: He, Ne, Ar

compounds

pure substances made when at least two elements chemically combine in fixed proportions

can be broken down chemically into simpler substances

compounds examples

water H₂O

carbon dioxide CO₂

sodium chloride NaCl

mixture

matter with at least two physically combined compounds

characterisitics of mixtures

variable composition

can be separated physically into simpler substances through

• filtration

• distillation

• evaporation

types of mixtures

homogeneous

heterogeneous

homogeneous mixtures

uniform composition

different components are evenly distributed and indistinguishable

homogeneous mixtures example

saltwater

air

heterogeneous mixtures

non-uniform composition

• different components can be seen + separated

• individual substances retain their properties

heterogeneous mixtures examples

salad

sand and iron fillings

oil and water

types of physical separating

separating by particle size

separating by density

separating by electric charge

separating by particle size

• sieving

• gravitational filration

• vacuum filtration

sieving

used to separate mixture of solids with different particle sizes

gravitational filtration

relies on the weight of solid particles to filter the two materials

vacuum filtration

faster than gravitational filtration

useful for light particles and you want to dry out the mixture

filtration

separate an insoluble substance from a soluble substance/solution

purpose of filtration

separate heterogeneous mixtures made of solids + liquids

how filtration works

porous barrier to separate the solid from liquid

liquid passes through barrier leaving solid in the filter paper

residue

collected solid

filtrate

collected liquid

separation by density

1. sedimentation

2. decantation

separation funnels

centrifugation

sedimentation

denser materials drop to the bottom

decantation

when the liquid at the top is poured away

separation funnels

used when liquids dont mix

tap at bottom to let densest material out

centrifugation

mixture is spun in a centrifuge to settle finer particles that do not settle naturally

process evaporation

1.preparation

2.heating

3.concentration

4.completion

preparation (evaporation)

place solution (containing a dissolved substance) in an evaporating dish/similar container.

heating (evaporation)

gently heat solution using a Bunsen burner/hot plate/water bath.

heat causes the solvent (usually water) to evaporate

concentration (evaporation)

solution becomes more concentrated with the dissolved substance as solvent evaporates

completion (evaporation)

continue heating until most of the solvent has evaporated, leaving behind the solid residue of the dissolved substance

crystalisation

formation of pure solid substances from solution (with dissolved substance)

process of crystalisation

solvent evaporates → dissolved substance comes out of solution → collects as highly pure crystals

crystalisation example

rock candy

distillation

separating mixtures based on differents in boiling points of their components

examples of distillation

labs

production of alcholic beverages

purification of watr

separation of petroleum products

process of distillation

1. heating

2. vapourisation

3. condensation

4. collection

5. residue

heating (distillation)

mixture is heated in distillation flask

component with lowest boiling point starts to vapourise first

vapourisation (distillation)

vapourised component travels up through distillation column.

condensation (distillation)

vapour reaches the condenser → cooled by water → condense back into a liquid

collection (distillation)

the condensed liquid (distillate) is collected in a separate container

residue (distillation)

remaining mixture in distillation flask (higher boiling point components) can be further processed or discarded

fractional distillation

separating mixtures of liquids based on the differences of boiling points of their components

fractional distillation examples

areas like

• pretoleum refining: separating crude oil into fractions like gasoline, diesel, kerosene

• labs: purifying chemicals + separating mixtures

process of fractional distillation

(have few very cool cool friends real)

1. heating

2. fractionating column

3. vapourisation and condensation'

4. collection

5. fraction collection

6. residue

heating (fractional distillation)

mixture is heated in a distillation flask

component with lowest boiling point starts to vapourise first.

fractionating column (fractional distillation)

vapour enters a fractionating column packed with materials like glass beads/plates.

large surface area for repeated condensation and vapourisation → better separation of components.

vapourisation and condensation (fractional distillation)

as vapor rises through the column, it cools and condenses on the packing material

heat from rising vapour causes the condensed liquid to vapourise again.

collection (fractional distillation)

vapour is cooled and condensed back to liquid in condenser

liquid (distillate) is collected in a separate container.

fraction collection (fractional distillation)

different fractions (components) are collected at different temperatures

controlling the temperature → component can be separated based on its boiling point.

residue (fractional distillation)

remaining mixture in the distillation flask, containing the higher boiling point components, can be further processed or discarded

electrostatic separation

used to separate particles based on their electrical charge

useful for fine particles

electrostatic separation process (charming few students cook)

1. charging

2. feeding

3. separation

4. collection

charging (electrostatic separation)

particles in mixture are given an electrical charge by passing them through an electric field

feeding (electrostatic separation)

charged particles are fed onto a conveyor belt/rotating drum

surface of belt/drum → grounded / has an opposite charge to attract the particles.

separation (electrostatic separation)

as they move along the belt/drum → particles with different charges will be attracted to different areas of the belt/drum → separating them based on electrical properties

collection (electrostatic separation)

separated particles are collected in different bins/containers.

chromatography

relies on how “sticky” material is to a static medium (resin, paper) → separates components of mixture

types of chromatography

paper chromatography (PC)

thin layer chromatography (TLC)

gas chromatography (GC)

high performance liquid chromatography (HPLC)

magnetic separation

used to separate materials based on their magnetic properties

magnetic separation examples

mining

recycling

food processing

process of magnetic separation

(fm asc)

1. feeding

2. magnetic field

3. attraction

4. separation

5. collection

feeding (magnetic separation)

mixture (magnetic + non-magnetic particles) of materials is fed onto a conveyor belt/magnetic separator

magnetic field (magnetic separation)

belt/ separator passes through a magnetic field made by a magnet/electromagnet

attraction (magnetic separation)

magnetic particles in mixure are attracted to magnetic field → attach to surface of belt/separator

non-magnetic particles are not affected and continue to move along the belt

separation (magnetic separation)

magnetic particles are carried away from the non-magnetic particles as the conveyor belt/ separator moves

magnetic particles are removed from the belt/separator, by scraper/ rotating drum.

collection (magnetic separation)

separated magnetic and non-magnetic particles are collected in different bins/containers

percentage composition

% by mass of each element in a compound

% by mass of a component in a mixture

use of percentage composition examples

nutrition

materials in science / chemistry

purpose of percentage composition

% composition of element as part of a compound

% composition of pure substance as part of a mixture

calculating percentage composition

ionic compound (salt)

substance formed from transfer of electrons between a metal and non-metal

uses of ionic compounds

fertilisers: salts such as ammonium nitrate can be used to grow fruits and vegetables.

food: salts such as sodium chloride and potassium iodate can be used to improve the taste of food.

fireworks/gunpowder: potassium nitrate can be used as a reagent in explosives.

toothpaste: sodium fluoride is used in dental hygiene.

pool chemicals: sodium hypochlorite is used to produce chlorine in pools.

cement/concrete: calcium oxide, or quicklime is an ingredient of cement.

forming ionic compounds

when metal and non-metal atoms react:

1. metals donate their electrons to non-metal → cations

2. non-metals receive electrons from metal → anions

3. electrostatic force forms between the anions and cations

4. new ions arrange themselves in large 3D lattice

5. ionic bonds hold lattice together

ionic bond

electrostatic between the anions and cations

electroconductivity of salt in different states of matter

solid: ions are fixed in place → cannot carry charge → will not conduct

liquid: ions are mobile → can carry charge → will conduct

electroconductivity of ionic compounds

solid: ions are fixed in place → cannot carry charge → will not conduct

liquid/molten: ions are mobile → can carry charge → will conduct

melting and boilting points (ionic compounds)

strong electrostatic forces of attraction → large amount of energy to disrupt them → higher temperature

melting points of ionic compounds

hard and brittle (ionic compounds)

ionic lattice made of alternating cation/anions

force applied → ions with similar charge repel → compound shatters

solubility (ionic compounds)

salt dissolved in water → ionic bonds break (dissociate) → ions form new forces with water molecules

size + charge of ions affect solubility

high lattice energy → hard to break apart → less soluble in solvents like water

properties of common salts

metallic bonding

electrostatic attraction between metals and a delocalised sea of electrons

• in pure metals + metal alloys

metallic bonding model

1. metals lose electrons → cation

2. cations arranged in lattice structure, surrouded by delocalised electrons

3. strong electrostatic forces of attraction between cations/anions hold metal together

metallic bonds are…

non-directional; occur in all directions between all metals ion and sea of electrons

electrical conductivity (metals)

1. voltage → delocalised electrons go to (+) terminal

1. cations are immobile while electrons are mobile

2. delocalised electrons can carry charge

3. good electrical conductivity

thermal conductivity (metals)

movement of delocalised electrons → heat (E_k) transfers quickly → good thermal conductivity

malleability and ductility (metals)

force applied → metal layers slide → non-directional metallic bonds between metal ions and delocalised electrons allows atoms to move without breaking → metal remains intact → malleable + ductile

tensile strength

how substance responds to force

tensile strength (metals)

strong electrostatic attraction between metal ions and delocalised electrons → requires more force to pull atoms apart → high tensile strength

lustre (metals)

free electrons reflect light → shiny appearance

melting and boilting points (metals)

strong electrostatic forces → high energy to break → high melting/boiling points

alloy

mixture of metals/metals + non-metal to enhance properties

alloys examples

• brass (copper + zinc)

  • stronger + more corrosion-resistant

• brass (copper + tin)

• stainless steel (iron + carbon + chromium)

  • more durable + rust-resistant

why alloys are strong

contain different-sized atoms → distort metal lattice → harder for layers to slide → increasing strength

uses of metallic bonding

1. electric wiring: Cu is great conductivity

2. construction materials: steel is strong + durable (eg. bridge, buildings)

3. jewellery: Au are is strong + shiny

4. aerospace + automotive: Al alloys are lightweight + corrosion-resistant

electroplating

process to coat surface of metal object with thin layer of another metal