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Module 1 Chemistry (NSW) Cheat Sheet (DRAFT) by

NSW Syllabus, Module 1 Chemistry ** Being added to

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Atoms, Elements and Compounds

Pure substances are made up of one type of atom
An element is a pure substance that cannot decompose into simpler substances
Compounds are formed by joining 2 or more elements; they can be broken down into simpler substances
Atoms of the same element are exactly alike
Atoms cannot be created, destroyed, or divided into smaller particles

Seperating mixtures

Sieving
Separates based on particle size
Filtration
One substance is a solid, other is a solution or liquid; particle size
Vapori­sation
Liquid has a much lower boiling point than the solid
Distil­lation
Big difference in boiling points
Fractional distil­lation
Signif­icant but small difference in boiling points
Separating funnel
Components are immiscible liquids; different densities
Adding a solvent
One sunbstance is soluble in the chose solvent, while the others are insoluble

Physical vs Chemical Change

Chemical
Physical
At least one new substance formed
No new substance formed
Difficult to reverse (hard to 'unboil' an egg)
Easily reversed (melt a solid; freeze again)
Generally large input and output of energy (burn natural gas)
Relatively small energy changes involved (evaporate alcohol, dissolve sugar in water)
In a chemical reaction the starting substances are called reactants and the substances that are formed are called the products.

The Periodic Table

Metals are elements that:
are solids at room temper­ature
 
have a shiny or lustrous appearance
 
are good conductors of heat and electr­icity
 
are malleable and ductile
Most other elements are called non-metals
The periodic table is a chart of the elements arranged so that those with similar properties fall into the same vertical column
The vertical columns are called groups, They are numbered from 1 to 18.
The elements in groups 3 to 12 are called transition elements. The other elements (in group 1, 2 and 13 to 18) are called main-group elements
The horizontal rows are called periods and they are numbered 1 to 7

Periodic Table cont.

Period­icity

The trends of the periodic table can be seen clearly in the image above.
The screening effect is the decrease in electr­ostatic force between a nucleus and an outermost electron brought about by completely filled electron shells between the nucleus and the outermost electron.
When an atom loses or gains an electron it becomes an electr­ically charged species because the numbers of protons and electrons are no longer in balance; becoming ions
First ionisation energy, IA, of an element is the energy required to remove an electron from a neutral gaseous atom of the element.
Electr­one­gat­ivity of an element is a measure of the ability of an atom of that element to attract bonding electrons towards itself in compounds.
The higher the electr­one­gat­ivity the stronger the attraction of the atom for bonding electrons.

Bohr vs Schröd­inger

Bohr
Considered electrons as particles orbiting the nucleus
 
Successful in interp­reting the hydrogen spectrum
 
Failed on more compli­cated ones.
Schröd­inger
Much more successful in interp­reting atomic and molecular proper­ties.
 
Showed that electrons move at extremely high speeds randomly in orbitals
Schröd­inger equation uses wave properties and quantum theory to calculate the probab­ility of finding an electron at a particular location
Planck’s quantum theory proposes that in atoms energy is not contin­uously variable but exists in discrete packages.
  

Atoms

An atom is the smallest particle of an element that is still recogn­isable as that element
The formula of a compound that exists as molecules is a combin­ation of symbols of the elements in the compound, with subscripts denoting how many atoms of each element are in the molecule
An atom consists of an extremely small dense nucleus or core, which contains the bulk of the mass of the atom and carries positive electrical charges
This nucleus is surrounded by an electron cloud of rapidly moving and extremely light negatively charged particles.
Atomic number, Z, of an element is the number of protons in the nucleus of an atom of that element.
The mass number, A, is the number of protons plus neutrons in the nucleus of an atom of the species concerned. Sometimes called the nucleon number
Number of electrons in the electron cloud is equal to the number of protons in the nucleus

Isotopes

Isotopes are atoms of one element that have different numbers of neutrons in their nuclei (although the same number of protons).
The relative abundance of an isotope is the percentage of that isotope in the naturally occurring element.
Isotopes of one element have the same chemical properties and very similar physical ones.

Radioa­ctivity

Radioa­ctive isotopes or radioi­sotopes sponta­neously emit radiation. They are also called unstable isotopes
Radioi­sotopes emit three types of radiation:
alpha (α) rays
which are helium nuclei
beta (β) rays
which are electrons
gamma (γ) rays
which are a type of electr­oma­gnetic radiation like light and X-rays
A nuclear equation shows the disint­egr­ation of a radioi­sotope into a new nucleus and a helium atom or an electron; the atomic and mass numbers must balance in nuclear equations.
The half-life of a radioi­sotope is the time required for half the atoms in a given sample to undergo radioa­ctive decay.
Half-life is indepe­ndent of the initial amount of the isotope present.

Spectr­oscopy

Electrons in an atom can be given extra energy and so be raised from its ground state into an excited state
When electrons in excited states fall back to their ground states, energy is released in the form of ultrav­iolet, visible and infrared radiation
This radiation can be analysed with a spectr­oscope
Measuring and studying the emission spectra of elements is called atomic emission spectr­oscopy.
Some elements produce distin­ctive flame colours because one particular electron transition occurs much more frequently than any other.
So a flame test can also be used to detect their presence in a sample

Period­icity

Chemical Bonding

Ionic
Outright transfer of electrons from one atom to another.
 
Electr­ostatic attran is between positive and negative ions
 
Ions are present in ratios, the total # of positive charges is equal to the total # negative charges
 
Formulaes (e.g. NaCl, CaF2 ) specify the ratios in which the ions are present, not the compos­ition of discrete molecules.
 
Ionic binary compounds are named positive ion then negative ion.
 
The positive ion has the same name as the element (e.g. ‘sodium’, ‘calcium’)
 
Negative ion the ending of the element name is changed to -ide.
 
High melting and boiling points
A polyatomic ion is an ion formed from two or more atoms joined together.
 

Electron Shells and Arrang­ements

Electrons orbit (move around) the nucleus in a circle called an electron shell.
These electrons exist in discrete energy levels
 
1st shell: holds 2 e-
 
2nd shell: holds up to 8 e-
 
3rd shell: holds up to 8 e-
Octet Rule: atoms are stable when their outer electron shell holds 8 electrons.
There are 2 exceptions to the octet rule.
 
1. The cases in which there are fewer than 8 electrons in the outer shell.
 
2. The cases in which there are more than 8 electrons in the outer shell. Exception: H and He.
Valence electrons: electrons in outer most shell of an atom that can partic­ipate in forming chemical bonds with other atoms
Atoms with a relatively empty outer shell will want to give up electrons
Atoms with a relatively full outer shell will want to gain electrons to fill up the outer shell
The arrang­ement of electrons in energy levels is called the electron config­uration of the atom.
The ‘driving force’ behind chemical reactivity is that an atom tends to lose, gain or share electrons in order to achieve the stable electron config­uration of the nearby noble gas.

Filling energy levels

Orbitals

Orbitals

Orbitals are a volume of space surrou­nding the nucleus of an atom through which one or two electrons may randomly move.
Each main energy level of an atom (except the first) is made up of a set of energy sublevels called the s, p, d and f sublevels.
Each orbital can accomm­odate a maximum of two electrons.

Ions

Ions are atoms with extra electrons or missing electrons
Ions are positively or negatively charged particles
Missing electrons results in a positive charge
Extra electrons results in a negative charge
Postive ions are called cations; negative ions are called anions
An ionic lattice is an orderly array of positive and negative ions
The formula of a compound that is made up of ions is a combin­ation of symbols of the atoms involved, with subscripts giving the ratio in which the elements are present in the compound (since there are no molecules of ionic compou­nds).