Chemistry Module 1- Explore
How do the properties of substances help us classify and seperate them?
Compounds
Mixtures
Elements
An element is a substance made from one type of atom. For example hydrogen.
A compound is a molecule made of atoms from different elements. For example water.
All compounds are molecules
All molecules are not compounds eg. hydrogen gas.
A mixture is a material made up of twi or more different substances. For example HCL
Homogeneous mixture - Has the same proportions of its compounds throughout any given sample. Eg. HCL
Heterogeneous mixture- Proportions vary throughout the sample. Eg. A cuppachino
Types of speration
Evaporation- Separate or homogenous mixtures where there is one or more dissolved solids.
Distillation- Separate mixtures comprised of two or more pure liquids. Distillation is a purification process where the components of a liquid mixture are vaporised and then condensed and isolated. In simple distillation, a mixture is heated and the most volatile component vaporises at the lowest temperature.
Decanting- In its simplest form, it just means allowing a mixture of solid and liquid or two immiscible liquids to settle and separate by gravity.
Filtration- Filtration is the separation method used to seperate out pure substances on mixtures comprised of particle some of which are large enough in size to be captured with a porous material.
Chromatography- Is the separation of a mixture by passing it in a solution or suspension or as a vapour through a medium in which the components move at different rates.
Gravimetric analysis
The procedure of gravimetric analysis:
Calculating gravimetric analysis
Gravimetric analysis is a technique through which the amount of an analyse (the ion being analysed) can be determined through the measurement of mass. Gravimetric analyses depend on comparing the masses of two compounds containing the analyte. The principle behind gravimetric analysis is that the mass of an ion in a pure compound can be determined and then used to find the mass percent of the same ion in a known quantity of an impure compound.
Weigh the sample to be analysed
Dissolve the sample in a suitable solvent, eg, water
Add an excess of the precipitating reagent to precipitate the analyte
Filter the mixture to separate the precipitate from the solution3
Wash the precipitate to remove any impurities4
Dry the precipitate by heating to remove water
Cool the precipitate in a dessicator to prevent the precipitate absorbing moisture from the air
Weigh the cooled precipitate
Repeat the drying and weighing process until a constant mass for the precipitate is achieved
Calculate the percent by mass of analyte in the sample
Write the balanced chemical equation for the precipitation reaction
Calculate the moles of precipitate: moles = mass ÷ molar mass
Calculate moles of analyte from the balanced chemical equation using the mole ratio of analyte : precipitate
(also known as the stoichiometric ratio of analyte to precipitate)
Calculate mass of analyte: mass = moles × molar mass
Calculate percent by mass of analyte in sample: (mass analyte ÷ mass sample) × 100
Why are atoms of elements different from one another
Electron energy levels
Generally symbolised by n, it denotes the probable distance of the electron from the nucleus. "n" is also known as the Principle Quantum number
Number of electrons that can fit in the shell: 2n^2
Using the Bohr Model
Bohr model electrons are in shells or energy levels
Electrons cannot exist between these levels
Electrons in an atom fill from the lowest energy level first
When an atom is heated, one or more electrons can be raised from
the ground state to an excited state
The excited electron/s will return to the ground state releasing a
quantum of energy in the form of a photon of light.
The greater the energy change the higher the frequency (shorter the
wavelength) of the emitted photon
Explaining the emission spectrum for hydrogen.
In hydrogen there are 4 lines in the spectrum.
A bit weird when you consider that an atom of hydrogen has only 1 electron
The electron can be excited to other energy levels. The ground level is the n = 1 level. Electrons can be excited to n = 2, n = 3, n = 4 etc.
The 4 visible lines in the hydrogen spectrum are excited electrons dropping from n = 6, 5, 4 and 3 down to n = 2.
Electron Orbitals
S Orbital
The s orbital has a spherical shape centered around the origin of the three axes in space.
P Orbital
There are three dumbbell-shaped p orbitals in each energy level above n=1 each assigned to its own axis in space
D Orbital
There are 5 d orbitals that are fund in the d sublevels beginning with n=3. To remember the shapes think double dumbbell and a dumbbell with a donut.
F orbital
7 shapes
What binds atoms together in elements and compounds? and How do the properties of substances help us to classify and separate them?
Electronegativity, Ionic and Covalent bonds
Covalent
Ionic Bonds- Ionic bonds have complete transfer of electrons and ocour with differences greater than 2.0
Polar covalent- Polar covalent bonds have unequal sharing of electrons and occur within differences less than 1.7
Non- Polar covalent- Covalent NP bonds have equal sharing of electrons and occur with differences less than 0.5
Nomenclatures of inorganic substances using IUPAC
Naming Binary covalent compounds
1) Element with the lowest group number written firts.
2) If in the same group element with the highest period number is written first.
3) Second highest element named with suffix - 'ide'
4) Greek prefixes are used to indicate the number of atoms in the molecule.
Anions and cations
Anions- Accept electrons from another atom to fulfil their valence electron outer shell.
Net charge is negative
Tends to form from atoms with 5 or more electrons in the outer shell
Cations- Lose electrons from to atom to fulfil their valence outer electron shell
Net charge is postiv
Tends to form from atoms with 3 or less electrons in the outer shell (metals)
Naming Ionic compounds
1) Cation w/ fixed charge has the same number as the neutral atom (na+ = sodium). Cations w/ variable are named as the element w/ the charge shown by roman numeral (Fe 3+= Iron (III))
2) Monatomic anions are written with a suffix. ie. ide
3) Polyatomic ions are written as they are named (NH4+= Ammonium
4) Cation name is written first, anion name is written second