Unit 1: Nature of Matter

Pure substances

• Fixed properties 

• Cannot be separated physically

Element 

• Same type of atom

• Cannot be broken down chemically

Compound 

• Two or more same types of atom chemically bonded

• Can be broken down chemically 

Mixtures 

• More than one compound/element

• Not chemically combined

• Can be separated physically

Heterogenous 

Different composition and properties 

• Defined borders

Homogenous 

Same composition and properties 

Solute 

SLG that dissolves in a liquid solvent to form a solution

Solubility 

Amount of solute to form a saturated solution

Saturated solution

No more solute can dissolve at a particular temperature

Miscible 

Capable of mixing to form a homogenous mixture 

Immiscible

Incapable of mixing and forms two separate layers instead 

Filtration

Type of mixture

Insoluble solid + liquid

What allows separation

Solubility 

Examples 

Sand and water 

Evaporation 

Type of mixture

Soluble solid + liquid 

What allows separation

Volatility: tendency to evaporate 

Examples 

Salt and water 

Recrystallization 

Type of mixture

Compounds with impurities 

What allows separation

Examples 

Questions 

What cannot be extracted by recrystallization? 

• When the solubility and temperature does not change a lot

• so there is a very small amount of () that will crystallise when a hot () is cooled

How to determine the mass that would be crystallized? 

• (original amount: check if it is soluble at that temperature first )-(mass of what the thing is when it is at the cooled temperature) g

Distillation 

Simple 

Fractional 

Type of mixture

Solvent from solution

(two or more) Miscible liquids with different boiling points

What allows separation

Boiling point

Examples 

Water from seawater 

Ethanol and water

Paper chromatography

Type of mixture

Soluble solids

What allows separation

Solubility (mobile phase) and attraction (stationary phase)

• Mobile phase: solvent 

• Stationary phase: chromatography

Examples 

Separation of dyes/pigments 

Questions 

How to calculate the Rf value?

Distance traveled by componentDistance traveled by solvent

Why must the solvent not surpass the origin line?

So that the mixture doesn’t dissolve in the solvent 

Why must the starting line be marked with a pencil?

So that the pen ink does not move up the chromatogram

Density 

• Mass per unit volume (g cm^-3)

Kinetic energy 

• Energy a particle has due to its motion (J)

Isotopes 

• Same number of protons and electron configuration

• Different number of neutrons

  • Nearly identical properties 

    • Similar chemical properties 

    • Slightly different physical properties 

• Not all are stable → which are called Radioisotopes

Radioisotopes 

Unstable form of an element that contains an unstable combination of neutrons and protons, therefore emitting nuclear radiation as it breaks down through radioactive decay and becomes more stable 

Relative isotopic mass (Ir)

= Mass of one atom of an isotope relative to 1/12 atom of carbon-12

= 12 units =( number of protons + neutrons) divided by 12 

Relative atomic mass(Ar): 

The average of the atomic masses in a sample 

Mass spectrometry 

Measures the:

1. Number of isotopes 

2. Relative isotopic mass

3. Relative abundance

Anion

• Negatively charged

• Gain electrons to become stable 

Cation

• Positively charged 

• Lose electrons to become stable 

Electromagnetic wave (light) 

• Higher frequency (number of waves that pass a point per second) → Higher energy

• Longer wavelength (distance between two neighbouring crests) → Lower energy

Wavelength: length of one wave

Frequency: number of waves per second

What happens when we multiply frequency and wavelength?

Speed of light

Electromagnetic spectrum

How to calculate the energy of an electromagnetic wave?

E=planck's constantfrequency=planck's constantspeed of lightwavelength

Emission line spectrum

• Produced when electrons fall from higher to lower energy levels, emitting light of specific wavelengths

The Bohr shell model

Lyman, Balmer and Paschen series:

• Every shell has a discrete energy level (n=x)

• Energy is lowest (longest wavelength) when closest to the nucleus, known as the ground state

  • Difference in energy decreases as distance from nucleus increase 

1. Heat/electrical energy allows electron to jump to higher energy level, known as an excited state (energy absorbed must be same difference between the two energy levels the electron is traveling between)

2. Drops back to original orbital and energy, as light/electromagnetic radiation is emitted (coloured light if wavelength same as visible region of electromagnetic spectrum)

When electrons jump from n infinity to:

N infinity → n1; UV

N infinity → n2; visible

N infinity → n3; infrared 

What can be determined from the energy associated with the line marked as ‘limit’?

Convergence limit: wavelength or frequency at which the spectral lines converge, 

• used to calculate the ionisation energy, which is the minimum energy required to remove one electron from one gaseous hydrogen atom

Orbital 

Where an electron is likely to be found = same energies 

• Each orbital holds maximum of two electrons that have opposite spin

  • This is called the Pauli exclusion principle  

Subshells = s(1) p(3) d(5) f(7) = similar energies 

Number of subshells = shell number = principal quantum number 

• The higher principal quantum number, higher energy

Filling of subshells and Orbitals 

Aufbau Principle

Filled from lowest to highest energy

Hund’s Rule

Every orbital in a subshell has to be filled with one electron with same spin before being filled with a second electron with the opposite spin 

Exceptions to look out for 

Chromium

Copper

Ground State VS Excited State 

To determine if an element is ground or excited just看哪个反常