Chemistry Test 2 Flashcards
How did Bohr confirm the existence of Electron shells?
He found the energy difference between levels by measuring the frequencies of emitted photons.
Bohr’s Discovery about Electrons and their Energy Levels
- Electrons orbit the nucleus in fixed energy levels
- Explained Electron Excitation, Electrons move up higher if they have more energy, shorter wavelength
- Other energy shells exist but electrons do not occupy it
- Electrons cannot be between levels
Electron configuration Maxes
1st Level Max: 2
2nd Level Max: 8
3rd Level Max: 8
4th Level Max: 2
Arrangement of Electrons effect?
The arrangement of the electrons into energy levels or shells is what determines the chemical behavior of an atom of an element.
Stability of the Valence shell effect?
The number of electrons in the valence shell of an atom determines its reactivity, tendency to form chemical bonds. A stable electron configuration is reached through the octet rule, this constitutes gaining or losing of electrons.
Isotopes Written Form IUPAC
Isotopes are written in the form with mass number in superscript to the left side of the element according to IUPAC
What properties of Isotopes are different?
Physical properties such as mass, inertia, density, melting, boiling and freezing point are different
Relative Atomic Mass
Relative Atomic Mass is defined as the ratio of the average mass of an atom (taking into account all isotopes and their natural abundances) compared to a 1/12 a Carbon-12 atom
Relative Atomic Mass formula
((%abundance of isotope x relative isotopic mass) + (%abundance x relative isotopic mass))/100
Mass Spectrometry Step 1: (Vapourised)
Sample is vapourised with extreme heat into gas form
Mass Spectrometry Step 2: (Ionised)
High Energy Electrons from an Electron gun bombard the sample atoms and knock off electrons ionizing them into cations.
Mass Spectrometry Step 3: (Acceleration)
Ions are accelerated so they all have the same kinetic energy (using accelerator plates)
Mass Spectrometry
Step 4: (Mass Tendency)
Inertia due to mass (tendency)
Mass Spectrometry:
Step 5: (Magnetism)
Amount of force ions feels from electromagnet is proportional to its charge.
Mass Spectrometry:
Step 6: (Deflection Part 1)
(Deflection due to charge)
Mass Spectrometry
Step 7: (Deflection Part 2)
Separated by mass (mass inertia comes in play with deflection due to charge)
Mass Spectrometry Step 8: (Detector)
Records Mass to charge ratios and isotopic. abundances
Mass Spectrum
A mass spectrum is the results produced by mass spectroscopy with relative abundance on y axis and mass to charge ratio (m/z) on x axis
Atomic Mass Calculation
Average of all isotopes of an atom
Relative Isotopic Mass
The ratio of the mass of an isotope of an element to 1/12 a Carbon-12 atom
How to calculate %abundance of an isotope from a Mass Spectra
Peak Height/Total Peak Height x 100
Properties of Elements Periodic table groups 7, 1, 2 and 8
Group 7 Halogens, Highly Reactive Group 1 and 2 metals are highly reactive Group 8 is inert, noble gases.
Atomic Radius Trend
Atomic Radius Trend is Increases down a group; as there are more energy levels and from right to left; decreased nuclear charge which leads to less pull of valence shells by lower positive charge
Electronegativity Definition and Trend w/ reason
Electronegativity is the ability for a neutral atom to attract valence electrons of an atom. Increase up a group; as there is less valence shells to disperse positive charge from nucleus which attracts electrons, increases from left to right; due to an increase nuclear charge which increase force of attraction.
1st Ionisation Energy Definition and Trend w/reason
1st Ionisation energy refers to the energy required to remove the most loosely bound electron of a neutral atom. Decreases down a group; due to increased number of valence shells occupied which results in valence electrons being removed with less resistance from nuclear positive charge. Increases left to right; due to an increased resistance from a high number of protons.
Electron affinity Definition and Trend w/o reason
Electron affinity is the potential energy change that occurs when electron/s are added to a gaseous atom. Increases to the right and up
Lewis Structures
Show they way that atoms share electrons when forming a molecule
What is a flame test?
A flame test is an analytical technique used to determine the presence of element in a salt or compound by colour. Elements absorb heat energy exciting electrons of different elements in different levels as they have distinct energy levels which causes the emission of specific discrete wavelengths only that element can emit when they return to ground state resulting in distinct colors which make up one main observable flame colour when state signifying the presence of a certain element. Uses nonluminous flame.
Flame Test Observed Colour (Absorption and Emission) and Electron Excitation Explanation
Flame tests rely on the transferring of energy by the electrons of the atoms through heat energy which excites electrons of a particular element in characteristic and distinct levels because they have distinct energy levels causing them to jump energy levels with the jump being proportional to energy absorbed. These excited electrons return back to ground state emitting the same energy absorbed in the form of visible light (photons) of specific wavelengths (emission spectra) which only that atom can emmit. These wavelengths are proportional to the jump back down to the ground state with a greater jump leading to a shorter wavelength and vice versa. These wavelengths emitted makes up the colour seen in the flame characterizing a specific elements presence.
Atomic Absorption Spectroscopy (AAS) (Absorption and Emission Excitation)
Atomic Absorption Spectroscopy is an analytical technique which is used to find the concentration of small traces of different elements in a solution. It utilizes the solution which is first aspirated through a spray chamber, combined with a fuel and its oxidant which allow combustion in the burner. The burner combusts the sample and atomizes it into gaseous free atoms in the flame. A cathode lamp of the specific element being analyzed is provided with electrical energy which excites the atoms in the element to specific energy levels which only that element can absorb due to their distinct energy levels which then is emitted in those specific wavelengths (emission spectra) which only that element can emit when the electrons return to ground state. These wavelengths are then absorbed by the free atoms which excites them as the wavelengths are nearly complementary to the element’s own absorption spectra. The rest of the light that is not absorbed is turned into one specific wavelength by a monochromator to be photo multiplied which turns the light into an electrical signal which is sent to the computer which spits out an absorbance value used to calculate concentration for a main solution
Calibration Curves, Calibration values and calibration solutions
Calibration curves shows the proportionality between an element’s absorbance value (y axis) and its concentration (x axis). A sample. Calibration solutions are a range of different solutions with set concentrations of the element being analyzed. These concentrations are called calibration values when the equivalent absorbance values are found. These values are used for the main solution when we have the absorbance but not the concentration so the concentration can be read off the calibration curve. A calibration curve is titled with the symbol for an element followed by the word calibration e.g. Au calibration
ppm and milligrams per liter equivalence point
When the solvent is water, these units are equivalent (density of 1 gm/ml)
