Chemistry

Question 1

Atomic Radius Trend Explained:

Answer 1

1. As you move down a group the atomic radius increases. This due to a new energy shell being added as the number of electrons increase more shells are required.

2.Atomic Radius also decreases from left to right in a period. This is due to an increase in nuclear charge in the atoms. The increase in protons will increase positive nuclear charge which will increase the force of attraction hence the electrons will be pulled to the nucleus closer.

Question 2

Ionization Energy:

Answer 2

Ionization energy measures the minimum amount of energy required to remove the most single most loosely bound electron from an atom in a neutral gaseous state.

Ionization energy increases from left to right in any periodic table/period.
This is because due to a decreased atomic radius and increased nuclear charge the valence electrons are attracted more strongly to the nucleus. Hence more energy is needed to overcome this force of attraction.

Ionization energy decreases down any group. This is due to the increased distance between the electrons and the nucleus and a greater number of electron shells, the positive nuclear charge has a lesser effect on the electrons therefore less energy is required to overcome this force of attraction.

Question 3

Electronegativity:

Answer 3

The ability of atom in a molecule to attract electrons to it self.

Electronegativity increases from left to right in any period of the periodic table. The number of protons increase as you move from left to right in a period. This increases the positive force of attraction on valence electrons/ have a stronger pull on the electron as well as a decrease in atomic radius.

Electronegativity decreases down a group of the periodic table. As you move down a group, the atomic radius increases. As the atomic radius increases due to more number of electron shells leading a weaker force of attraction on the valence electrons from the nucleus.

Question 4

Relative Atomic Mass

Answer 4

Chemist have chosen a standard by which we measure the mass of atoms. The chosen standard mass of the most common isotope is carbon -12. The mass of an isotope compared to an mass of the isotope carbon 12 is called relative atomic mass.

Question 5

Mass Spectrometry

Answer 5

This a technique that can be used to measure the mass of atoms or molecules.

When we use it for elements it can help us determine the relative abundance and presence of isotopes.

Question 6

Mass Spectrometers

Answer 6

-Separates individual isotopes in an element
-Determine the mass of each isotope relative to carbon -12.
-Calculates the relative atomic isotopic abundance of each isotope.

Question 7

How does Mass Spectrometers Work:

Answer 7

1. The sample is vaporized and then ionized using high energy electrons.
   2.The ions are separated and accelerated according to their mass to charge ratio. The ions go pass a magnetic field.
   3.Particles with a larger mass experience less deflection.
2. Particles with larger charge experience a larger deflection. The charged particles that got deflected by the magnetic field will hit the detector.
   5.Ions that have a particular mass to charge to ratio are detected by a device that counts the number of ions that hit it.

The information that is spat out by the mass spectrometer is called mass spectrum.

Question 8

Separation by Particle Size:

Answer 8

1. Gravitational filtration is when you rely on the weight of the solid particles to filter the two materials.

2.Vacuum filtration is faster than gravitational filtration, it is then useful if the particle are light and you want to dry out the mixture.

3.Sieving is used to separate a mixture of solids with different particles size.

Question 9

Filtration:

Answer 9

Filtration can be used to separate an insoluble substance from a soluble substance.

Used to separate heterogenous substances, composed of solids and liquids.

Uses porous barriers to separate the solid from the liquid.

Liquid passes through leaving the solid in the filter paper.

Question 10

Separation by Density:

Answer 10

Sedimentation is when the more dense material drops to the bottom, decantation is when you pour the liquid at the top away.

Separation funnels can be used when liquids don’t mix, the funnel has a tap at the bottom and you can let the most dense material out.

Centrifugation is when we spin a mixture in a centrifuge, this helps to settle finer particles that may not settle naturally.

Question 11

Separation by boiling:

Answer 11

Evaporation is when you boil off the liquid(solvent) and it leaves the dissolved material solute behind.

Distillation uses evaporation but then also collects the gases, the condenser converts the gas back into a liquid and it is collected in a flask.

Fractional distillation is used for mixtures that have many different substances in them, that all have slight different boiling points.

Distillation and evaporation is used to separate homogeneous mixtures.

Based on differences in boiling points of substances involved. Evaporation can be used to separate a solute from the solvent in a solution.

Question 12

Crystallization:

Answer 12

Crystallization is a separation technique that results in the formation of pure solid particles from a solution containing a dissolved substance.

As one substance evaporates, the dissolved substance comes out of the solution and collects as crystals.

Produces highly pure solids.

Question 13

Separation by electric charge:

Answer 13

Electrostatic separation can be used to separate the charged solid particles from a gas

Chromatography is a technique that relies on how ‘sticky’ one material is to the static medium, this separates the mixtures component of a mixture out.

Question 14

Magnetic Separation

Answer 14

Can be used to separate the magnetic substances from a non-magnetic substance.

Question 15

Spectra

Answer 15

Spectra is the refer to the unique patterns of electromagnetic radiation emitted or absorbed by atoms when electrons transition between energy levels.

1. Light is part of the electromagnetic spectrum.
   2.Electrons orbit the nucleus in fixed energy shells and at a fixed distance from the nucleus.
   3.Electrons that orbit the nucleus further away will exist at higher energy levels.

3.If energy is absorbed electrons can jump to an excited state and if the energy is removed, the electrons will move back to its ground state. As a result a photon is been emitted (light particle with no mass).

How can we excite electrons:
1.Spark 2. heat 3.Light 4.

Question 16

Absorption Emission Spectra:

Answer 16

The energy absorbed by the electron to go from a ground state to an excited state is equal to the energy released or emitted by the electron upon returning to ground state.

The energy emitted or absorbed in the electron transfers of a given element are unique for that element and thus the resulting line spectrum is also unique.

Question 17

Atomic Absorption Spectroscopy:

Answer 17

Spectroscopy - study of the interaction between light and matter.

AAS - an analytical technique that relies on unique nature of an element’s absorption spectrum to identify its presence and concentration in a mixture.

AAS - works as an element in the gaseous phase can absorb only certain specific wavelengths of light called absorption spectrum.

Question 18

Homogenous Substances:

Answer 18

–A homogenous substance is though of which the components are uniformly distributed throughout the mixture.
1. Only 1 type of atom
2. 2 or more chemically combined elements not easily separated from each other.
3) Solution - a special kind of mixture 2 phases/parts

Question 19

Heterogenous Substances

Answer 19

1) Means different throughout
2) Always a mixture
3) 2 or more physically combined substances

Question 20

Homogenous Mixtures:

Answer 20

It is a mixture where the components are evenly distributed among each other. Homo - same
It has a constant composition throughout.
It is also called solutions.

Question 21

Heterogenous Mixtures:

Answer 21

The components are not evenly distributed among each other. A heterogenous mixture has two or more distinct phases that are usually detectable.
These type of mixtures do not have uniform properties. Heterogenous mixtures that look like solutions can be distinguished as they scatter light.

Question 22

Colloid

Answer 22

A colloid is a Non-transparent 2.Non-uniform 3.Large particles 4.Cloudy but a stable system.

Question 23

Suspension

Answer 23

A suspension of liquids droplets or fine sold particles

Question 24

Atomic Absorption Spectroscopy:

Answer 24

This is a technique that is used to determine the concentration of different elements in solution.

Concentration Values:
1.Milligrams per liter: how many milligrams of solute per liter of solution.
2.Parts per million: how many parts of an element there are per one million particles of solvent.

This technique involves focusing light of a specific wavelength on atoms of a solution and measuring the amount of light that it has absorbed.

The measurement of light the substance has absorbed is called absorbance.

Absorbance can be used to measure concentration.

Question 25

How does Atomic Absorption Spectroscopy work:

Answer 25

1. A flame to act a heat source.
   2.A method of spraying the sample solution into the flame.
   3.A beam of light for the atoms to absorb.
   4.A way to focus and detect light.
   5.A device to show the calibration graph and calculate results.

Question 26

Detailed Steps of AAS

Answer 26

The burner is a steel plate with a thin slit for flammable gas and sample mixture to come through.

An ignitor sets the gas alight by quickly shotting a flame across it.

The sample is drawn through a thin tube into a box called a spray chamber.

The solution is turned into a spray and mixed with flammable gas mixture of air and acetylene

The instrument uses a hollow cathode lamp. This provides a beam of light specific to an element.

The atoms in the flame absorb this light.

The light which is not absorbed is focused by a monochromator and measured by a detector.

The amount of transmitted light is used to calculate the amount of absorbed light.

The amount of transmitted light is used to calculate the amount of absorbed light.

Photomultiplier tube, is a special device which is used to measure light and convert it to electrical signal.

Question 27

A solution

Answer 27

A solution is a homogenous mixture composed of two or more substances that are evenly distributed at the molecular or atomic level.