IGCSE Chemistry (Co-ordinated Sciences Double Award 2024)

Solid to gas

sublimation

solid properties

Fixed shape and volume, particles close together, lattice arrangement, strong attraction, vibration

liquid properties

Takes shape of container, fixed volume, particles together, intermediate, little order in arrangement, moderately weak attraction, can vibrate rotate and translate

Gas properties

Takes shape and volume of container, particles far apart, move randomly, very weak attraction, can vibrate, rotate, translate

Diffusion

net movement of particles from an area of their higher concentration to an area of their lower concentration

How does temperature affect rate of diffusion?

The higher the temperature, the faster the rate of diffusion. This is because the particles have more energy so they move around faster

How does particle mass affect diffusion?

The lower the particle mass, the higher the rate of diffusion

Why are there flat lines on heating curves?

Because all of the kinetic energy is going to breaking the attraction between the particles so the temperature does not increase

Pure substances melt and boil at a

Single temperature

Mixtures melt and boil over a

Range of temperatures

No two substances have the same

Melting/boiling point, Rf,

Pure substance

Made up of one type of particle

Mixture

Two or more types of particles, not chemically bonded

Element

The simplest form of a substance, can not be broken down into a simpler substance

Atom

Smallest particle of an element, always neutral

Ion

Charged particle, either cation (positive) or anion (negative)

Compound

More than one atom chemically combined, can be molecular (non metal only) ionic, or giant covalent (add to this)

Molecule

two or more atoms held together by covalent bonds (non metals only)

Metal properties

Shiny, malleable, ductile, conductive of heat/electricity, silver (except for Au and Cu)

WHEN DRAWING A DIAGRAM

lines must touch the thing they are labeling

Solute

Dissolved in a solvent to make a solution

Solvent (normally water in igcse)

Dissolves the solute (solute particles fit in the spaces between solvent particles)

Solution

Mixture with one visible phase (thing you can see)

concentration of a solution

Quantity solute/quantity solution

Concentration is the same no matter

Volume

Suitable solvent

A solvent that dissolves part of the mixture but not the other so that one part can be obtained

When describing a change,

Say before and after, etc. white to blue

Rf (retention factor)

distance traveled by solute/distance traveled by solution. The higher the Rf, the more soluble the solute

Anything white dissolves...

Clear

homogeneous solution

a mixture in which you cannot see the different parts, is uniform

heterogeneous mixture

A mixture in which different materials can be seen/distinguished easily

Why is purity important?

Food poisoning, allergies, cultural guidelines,,impurities in medicine, dangerous side effects, changed effective dose

Physical change indicators

Change of state, shape, size, dissolving, can be separated by methods we learned

Chemical change indicators

NEW SUBSTANCE PRODUCED-new color, smell or bubbles (gas produced), energy released or absorbed (thermal, electromagnetic radiation, light, sound), precipitate formed, cooking

2 CHEMICAL CHANGES THAT CAN BE REVERSED

Copper (II) sulfate-anhydrous is white, hydrated is blue, can boil/add water to reverse

Cobalt (II) chloride-anhydrous is blue, hydrated is pink, same process as above to reverse

Proton info

Charge +1, mass 1, found in the nucleus.

Electron info

Charge -1, mass 0 (negligible), found outside nucleus on shells

Neutron info

Charge 0, mass 1, found in nucleus

atomic number

number of protons

Mass number

the sum of the number of neutrons and protons in an atomic nucleus

Relative atomic mass

Mass number rounded (??)

Standard atomic motation

Mass number on top, atomic number on bottom

In the periodic table, elements are arranged...

In ascending atomic number

The group number is equal to

number of valence electrons

The period number is equal to

number of energy shells

What affects the identity of the element

Number of protons

Isotopes

Atoms of the same element that have different numbers of neutrons (different mass)

Why do isotopes have the same chemical properties?

Because the electron arrangement is the same

Across a period, metallic character

Decreases

Metals have a _____ valence shell

Less than half full

Non-metals have a _____ valence shell

More than half full

(???) Metalloids have a ________ valence shell

Half full

As the number of valence electrons increase,

Metallic character decreases

Metallic properties are caused by

The little amount of valence electrons

Trends in group 1

gets more reactive, becomes softer, lower melting point

when doing a test question comparing isotopes

use specific numbers, ex state exactly how many more neutrons does it have (like on the practice test)

how can hardness be explained by particle attraction

scratching something is removing particles so the stronger the metallic bonds (??), the harder it is to separate from the rest

Alkali metal + water

metal hydroxide + hydrogen

Why are noble gases unreactive?

They have a full valence shell

uses of noble gasses

argon in lamps, helium in balloon

halogens exist as

diatomic molecules (o2, Br2, I2, etc.)

Trends in group 7

darker color, increase density, increase melting and boiling point, decrease reactivity

7 diatomic elements

H, N, O, F, Cl, Br, I (looks like a 7 on periodic table +H)

Halide

stable, unreactive ion of a halogen (exists as part of ionic compound)

halogen/halide reactions

a more reactive halogen will displace a less reactive halogen's halide ion from a compound

the octet rule

atoms tend to gain, lose (ionic bonding) or share electrons (molecular bonding) until their valence shell is full.

Anions are formed when

non metal atoms gain electrons

Cations are formed when

metal atoms lose electrons

transition metals

high densities, high melting points (relative to other metals)

in ionic compounds, transition metals are

colored solids that dissolve in water to form colored aqueous solutions (other ionic compounds not containing transition metals are white solids)

transition metals and/or their ions often act as

catalysts

ionic compound

oppositely charged ions electrostatically attracted

ionic bond

electrostatic attraction between oppositely charged ions

EXAMPLE EXPLANATION OF IONIC COMPOUND --> Describe the formation of k2s

draw diagram
potassium atoms transfer electrons to sulfur atom
1. 2 atoms of potassium lose 1 valence electron each, forming 2 1+ ions (or 2 K+ ions)
2. 1 sulfur atom gains 2 electrons forming an S2- ion
3. 2k+ and s2- form an ionic compound (held together by ionic bonds)

arrangement of ions

as solids, ionic compounds exist as a 3D lattice structure held together by strong ionic bonds (electrostatic attraction) the ionic bonds are arranged to maximize attractions and minimize repulsions. Each ion is ionically bonded to 6 oppositely charged ions.

metal element + nonmetal element -->

ionic compound

nonmetal element + nonmetal element -->

covalent compound

(simple) molecules (molecular compound, covalent compound)

nonmetal atoms held together by very strong covalent bond

covalent bond (molecular bond)

pair of electrons shared between non metal atoms (in a molecule) (bonding pair electrostatically attracted to nuclei of 2 nonmetal atoms)

electrical conductivity

allowing electrical current (charged particles-electrons or ions) to pass through

volatility

tendency to turn into a gas, affected by bond strenght

combining capacity

the number of covalent bonds an atom forms (in a molecule). This is equal to the number if unpaired valence electrons (in dot and cross)

in a dot and cross diagram, atoms with highest combining capacity go

in the center of the molecule

bonds-strongest attraction to weakest attraction

covalent bonds, ionic bonds, metallic bonds, intermolecular attractions (by a lot)

factors affecting physical properties

ONLY bond strength of (named) attractions between (named) particles can be used to explain physical properties

SAMPLE TEST Q explain the difference in melting + boiling point of ionic and covalent compounds in terms of attractive forces (same q can also be asked giving compounds, identify which is ionic and which is covalent and then answer)

1. ionic compounds have higher melting + boiling points than covalent compounds
2. ionic solid-ions held in a lattice by strong electrostatic attractions between oppositely charged ions.
3. covalent solid-atoms held together by weak intermolecular attractions
4. therefore, less energy required to break weaker intermolecular bonds

carbon exists in many forms/structures including

diamond and graphite

Diamond C(s) arrangement

each carbon atom forms 4 single covalent bonds wit 4 other carbon atoms

3 giant covalent structures

Diamond, graphite, silicon dioxide

Structure of graphite

rings of 6 atoms that form a sheet. Each atom is bonded to 3 others. The extra electron goes in between the sheets making them able to conduct electricity.

Why is graphite used as a lubricant?

Because the layers are held together weakly so are free to move over each other

ionic compound melting, volatility, solubility, electrical conductivity

Nacl, CuS, high melting, low volatility (strong ionic bond), most dissolve in water others in oil, as solids do not conduct bc no free charged particles, as liquids do because free ions

covalent compound melting, volatility, solubility, electrical conductivity

H20, CH4, CO2, low melting, high volatility (weak intermolecular bond), solubility in either water or oil, do not conduct electricity bc no free charged particles

giant covalent compound melting, volatility, solubility, electrical conductivity

SiO2, diamond, graphite, high melting, low volatility (strong covalent bond) not soluble (too big to fit in the spaces between solute molecules) diamond and SiO2 no bc no free to move charged particles, graphite yes bc delocalized free to move electrons

Structure of SiO2

each Si forms single covalent bond with 4 O atoms, each O atom forms single covalent bond with 2 Si???????

metal + acid -->

hydrogen + salt

acid + metal oxide (O)/hydroxide (OH) -->

water + salt

acid + metal carbonate (CO3)/hydrogen carbonate (HCO3) -->

water + CO2 + salt

nonmetal (molecular) oxides are

acidic

metal (ionic) oxides are

basic