Chemisry (Trends of the Periodic Table & Atomic Absorption Spectometry)

Question 1

Trends of the Periodic Table

Where are metallic elements found on the periodic table?
Trend of metallic elements in the periodic table?
What is the least metallic element and the most metallic?

Answer 1

The most metallic elements are found on the left-hand side of the Periodic table and they become less metallic from left to right.
The elements also become more metallic from top to bottom.
Helium is the least metallic element and Francium is the most metallic.

Question 2

Trends of the Periodic Table

What is atomic radius and the trend on the periodic table?

Answer 2

Refers to the distance from the centre of the nucleus of an atom to the perimeter of the highest energy level.
The atomic radius increases down a group because with each period there is another shell added.
The atomic radius decreases from left to right across a period because the number of shells hasn’t changed but there are more protons in the nucleus.
This pulls on the electrons, bringing them closer to the nucleus and making the atoms overall size smaller.

Question 3

Trends of the Periodic Table

What is valency and its trend on the periodic table

Answer 3

Refers to the number of electrons on the outer shell.
Valency increases across group #.

Question 4

Trends of the Periodic Table

What is electronegativity?
What is the trend on the periodic table?
What elements have the highest and lowest electronegativities?

Answer 4

The affinity (love) of an atom for electrons.

The higher the electronegativity, the smaller the atom.

Electronegativity increases as you move from left to right across a period and decreases as you move down a group.

This means that francium would be the element with the lowest electronegativity and the element with the highest electronegativity is fluorine (the noble gases are excluded as they have a full outer shell and are unreactive).

Question 5

Trends of the Periodic Table

What is the first ionisation energy and its trend on the periodic table?
What are the common valency properties of high and low F.I.E elements?
What is the highest and lowest element of F.I.E?

Answer 5

Refers to the amount of energy that it would take to remove one electron from an uncharged atom.

F.I.E decreases down the group and increases across periods.

Low F.I.E would mean a low amount of valence electrons, High F.I.E means a high amount of valence electrons (i.e. non-metals).

Because of the attractive force of the nucleus, a smaller atom will have a higher first ionisation energy.

Francium will have the lowest first ionisation energy and helium will have the highest first ionisation energy.

Question 6

Atomic Structure

Where are the lowest and highest energy levels?

Answer 6

The lowest energy levels are closest to the nucleus and the highest energy levels are furthest.

Question 7

Absorption and Emission

Describe how atoms emit light

Answer 7

After absorption, electrons move back to the state of a lower energy level (towards the nucleus). This movement causes an emission of light.

Question 8

Absorption and Emission

What do absorption and emission spectrums do?

Answer 8

An absorption spectrum shows what happens when an atom absorbs certain frequencies of light. The dark stripes represent the light that is absorbed. An emission spectrum shows the frequencies that are emitted. You can see that the emission spectrum fits over the absorption spectrum.

Question 9

Absorption and Emission

Use of absorption and emission spectrums

Answer 9

Help us determine the composition of stars
The concentration of carbon dioxide in the atmosphere

Question 10

Atomic Absorption Spectroscopy

What is Atomic Absorption Spectroscopy used for?

Answer 10

It is used to measure concentration through the absorbance of light. Used in industries such as the geochemical (mining), environmental management and agricultural industries.

Question 11

Absorption and Emission

How does Atomic Absorption Spectrometry work

Answer 11

involves focusing the light of a specific wavelength on atoms of a solution and measuring the amount of light absorbed. This is done by producing a set of solutions only containing the element we need with a range of concentrations. Then the concentrations of the solutions are run on the instrument and the absorbance is measured. Then it is plotted and read off the value from the graph.

Question 12

Absorption and Emission

Units used in AAS

Answer 12

Parts per Million (Ppm) equal to milligrams per litre (mg per L)

Question 13

Atomic Absorption Spectrometry

Instruments used in AAS

Answer 13

• Sample Introduction (Nebulizer and Spray Chamber)
• Burner
• Hollow Cathode Lamp
• Monochromator
• Detector
• Computer

Question 14

Atomic Absorption Spectrometry

What is the Sample Introduction System

Answer 14

Consists of a nebulizer and spray chamber. The nebulizer is used to fine the solution into a thin form and into a spray-like shape. The spray chamber then adds the flammable gas into the solution and contains the substance.

Question 15

Atomic Absorption Spectrometry

What is the burner

Answer 15

The burner flows the substance into an even thinner sheet, and ignites the solution into a flame.

Question 16

Atomic Absorption Spectrometry

What is the Hollow Cathode Lamp

Answer 16

The Hollow Cathode Lamp is used to produce a beam of light that passes through the flame with a specific wavelength only absorbed by atoms of that element in the flame.

Question 17

Atomic Absorption Spectrometry

What is the monochromator

Answer 17

An instrument used to fine and focus the beam of light that passes into the detector.

Question 18

Atomic Absorption Spectrometry

What is the detector

Answer 18

An instrument that converts the beam of light into an electrical signal (Absorbance)

Question 19

Atomic Absorption Spectrometry

What is the data reader

Answer 19

Reads the beam of light as absorbance which is a display of the result.

Question 20

Isotopes and Relative atomic mass

What is an Isotope

Answer 20

An element with a different amount of neutrons. Usually have the same chemical properties of the element, but have different physical properties.

Question 21

Isotopes and Relative atomic mass

Uses of Isotopes

Answer 21

Geological experiments: isotopes of carbon, oxygen and sulfur can be used to determine mineral composition.
Radiocarbon dating: used to determine the age of different objects based on their C-14 composition.
Treatment of cancer: radioactive isotopes emit gamma rays which target and damage cancerous tumours.
Food irradiation: gamma rays emitted from radioactive isotopes are used to kill bacteria.
Treatment of hyperthyroidism: I-131 is used to suppress thyroxine production in the thyroid gland.
Source of electric power: isotopes can be used to generate electricity.

Question 22

Isotopes and Relative atomic mass

What is Relative Atomic Mass and how is it calculated

Answer 22

The average mass of its atoms, compared to 1/12 of the mass of a carbon atom. Calculated by: (Mass of isotope * Abundance)/100.

Question 23

Mass Spectrometry

What is Mass Spectrometry

Answer 23

Mass spectrometry is an analytical technique where ions are sorted, detected and counted based on their mass to charge ratio. The mass to charge ratio is calculated by taking the atomic mass of the isotope and dividing it by the charge on its ion. For example, the mass to charge ratio of magnesium-24 would be (24 / 2 = 12).

Question 24

Mass Spectrometry

Mass Spectrometry as a quantitative analysis

Answer 24

Mass spectrometer can be used to determine the concentration of elements or compounds in a solution. Like atomic absorption, calibration solutions are analysed, and the concentration of these solutions is measured against counts per second to give a calibration graph. The samples are then analysed and their concentrations read off the calibration graph.

Question 25

Mass Spectrometry

Mass Spectrometry as a qualitative analysis

Answer 25

A mass spectrometer can be used to identify the components of a solution by producing a mass spectrum. A mass spectrum is a chart that shows the abundance of each isotope of each element in the solution. The components are shown in order of mass-to-charge ratio. The composition is shown as percent abundance.

Question 26

Process of Mass Spectrometry

Answer 26

Vaporisation: Sample is sucked up by pumping it into a glass chamber. As it passes through a tiny tube called a nebulizer it forms a fine spray. Mist is drawn into a tube called a torch where it reaches an ionisation source (plasma).

Ionisation: Plasma is at extremely high temperature (10000 kelvin). As the mist enters the plasma the liquid evaporates and all that is left is ions. The ions are focused using cones to form an ion beam.

Acceleration & Deflection: The ion beam is then accelerated through a set of magnetic rods called a quadrupole. The rods deflect one type of ion toward the detector. All other ions are “vacuumed” out to waste.

Detection: The detector for the instrument is called an electron multiplier. It counts each ion as it comes out the other end and displays the results as a mass spectrum.

Question 27

Describe how atoms absorb light?

Answer 27

Electrons move to a state of a higher energy level from a state of a lower energy level (at the nucleus) . This movement causes an absorption of light.