Topic 1 - Atomic Structure and the Periodic Table Flashcards
What are the 3 subatomic particles?
- Protons
- Neutrons
- Electrons
Describe the structure of an atom.
- Nucleus with protons and neutrons
* Electron shells around the nucleus
Compare the size of the nucleus with the size of the whole atom.
Its diameter is relatively tiny.
What subatomic particles make up the nucleus?
Protons and neutrons
Where is most of the mass of the atom found?
The nucleus.
How are the masses and charges of subatomic particles given and why?
- As RELATIVE masses and RELATIVE charges
* Because the actual mass and charge values are tiny
What is the relative mass and charge of a proton?
Mass: 1
Charge: +1
What is the relative mass and charge of a neutron?
Mass: 1
Charge: 0
What is the relative mass and charge of an electron?
Mass: 0.0005
Charge: -1
What is a nuclear symbol?
- The symbol for an element found in the periodic table that shows its mass number and atomic number.
- e.g. 7Li3
What is the mass number?
The number of protons and neutrons in an element.
What is the symbol for the mass number?
A
What is the atomic number?
The number of protons in an element.
What is the symbol for the atomic number?
Z
What is another name for the atomic number?
Proton number
What identifies a particular element?
The atomic/proton number.
In a neutral atom, the number of protons equals…
The number of electrons.
How can you find the number of neutrons in an element?
No. of Neutrons = Mass number - Atomic number
What causes a negative ion to have a negative charge?
It has gained electrons (so it has more electrons than protons).
What causes a positive ion to have a positive charge?
It has lost electrons (so it has more protons than electrons).
What are isotopes?
Atoms with the same number of protons but different numbers of neutrons.
Give an example of isotopes.
Cl-35 and Cl-37.
What determines the chemical properties of an element?
The number and arrangement of electrons.
What determines the physical properties of an element?
Usually the mass.
Compare different isotopes in terms of chemical and physical properties and explain why this is.
- Same chemical properties -> Same electron configuration
* Different physical properties -> Different masses
What is the difference between physical and chemical properties of an element?
- Physical -> Can be observed without changing the element (e.g. colour)
- Chemical -> Can only be observed by changing the chemical identity (e.g. flammability)
What is relative atomic mass?
The weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12.
What is the symbol for relative atomic mass?
Ar
What is relative isotopic mass?
The mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12.
What is the difference between relative isotopic mass and relative atomic mass?
Relative isotopic mass refers to only one isotope, while relative atomic mass takes into account all of the different isotopes of an element.
Are relative atomic mass and relative isotopic mass whole numbers?
- Relative atomic mass - Usually not a whole number
* Relative isotopic mass - Usually a whole number
A natural sample of chlorine contains a mixture of Cl-35 (75%) and Cl-37 (25%). What are the relative isotopic masses and relative atomic mass?
- Relative isotopic masses - 35 and 37
* Relative atomic mass - 35.5
What is relative molecular mass?
The average mass of a molecule or formula unit compared to 1/12th of the mass of an atom of carbon-12.
What is the symbol for relative molecular mass?
Mr
What two things does relative molecular mass encompass and when is each used?
- Relative molecular mass -> For simple molecules
* Relative formula mass -> For ionic and giant covalent compounds
How do you find the relative molecular mass?
Add up the Ar values of all of the atoms in the molecule.
How do you find the relative formula mass?
Add up the Ar values of all of the atoms in the formula.
Ar: C = 12, H = 1, O = 16Find the relative molecular mass of C2H6O.
Mr = (2 x 12) + (6 x 1) + 16 = 46
Ar: Ca = 40.1, F = 19Find the relative formula mass of CaF2.
Mr = 40.1 + (2 x 19) = 78.1
Compare the Ar of an atom and an ion.
They are the same.
What is isotopic abundance?
The amount of a particular isotope as a percentage of all of the atoms of an element.
How can you calculate the Ar of an element from its isotopic abundances?
1) Multiply each relative isotopic mass by its % abundance and add these up.2) Divide by the total % abundance (usually 100).
20% of all boron atoms on earth have a relative isotopic mass of 10.0, while 80% have a relative isotopic mass of 11.0. Find the Ar of boron.
• (20 x 10) + (80 x 11) = 1080• 1080 / 100 = 10.8
What is a mass spectrum?
A bar graph of mass to charge ratio (x) against abundance (y) of different isotopes (or other particles).
What device produces mass spectra?
Mass spectrometers.
What is a mass spectrometer?
- A device that is used to find out what samples are made up of by measuring the masses of their components
- Produces mass spectra
What can mass spectra tell us?
- Relative isotopic masses and abundances
* Relative atomic masses of different elements
What is on the y-axis of a mass spectrum?
Abundance of ions (as a number or percentage).
What is on the x-axis of a mass spectrum?
Mass to charge ratio (m/z).
For the mass spectrum of an element, what does the height of each peak give?
The relative isotopic abundance of that isotope.
On the x-axis of a mass spectrum, what is m/z?
The mass to charge ratio of the ion.
For the mass spectrum of an element, what does the m/z value usually correspond to and why?
The relative isotopic mass, since the charge is usually +1.
How can you work out the Ar of an element from its mass spectrum?
1) Multiply each relative isotopic mass (x-axis) by its abundance (y-axis) and add these up.
2) Divide by the sum of the isotopic abundances.
Practice calculating the Ar of an element from its mass spectrum.
Pg 7 of revision guide.
Silicon can exist in three isotopes. 92.23% of silicon is Si-28 and 4.67% is Si-29. The Ar of silicon is 28.1. Calculate the abundance and isotopic mass of the third isotope.
1) Abundance of third isotope = 100 - 92.23 - 4.67 = 3.10%
2) Let X equal the final isotopic mass
• 28.1 = ((28 x 92.23) + (29 x 4.67) + (X x 3.10) / 100
• 28.1 = (2717.87 + (X x 3.10)) / 100
• 2810 - 2717.87 = X x 3.10• 29.719 = X
• So the final isotope is Si-30.
Describe how you can predict the mass spectrum for a diatomic molecule.
1) Express each abundance as a decimal (e.g. 75% = 0.75)
2) Make a table showing all of the possible combination of atoms in the molecule.
3) For each molecule, multiply the abundances to get the abundance for the molecule.
4) Look for any molecules that are the same and add up their abundances. (e.g. Cl-37, Cl-35 and Cl-35, Cl-37 are the same).
5) Divide all of the relative abundances by the smallest relative abundance to get the smallest whole number ratio.
6) Use these values to predict the heights of each peak on the mass spectrum.
Chlorine has two isotopes. Cl-35 has an abundance of 75%. Cl-37 has an abundance of 25%. Predict the mass spectrum of Cl2.
1) Table of abundances:
• Cl-35, Cl-35 = 0.75 x 0.75 = 0.5625
• Cl-35, Cl-37 = 0.75 x 0.25 = 0.1875
• Cl-37, Cl-35 = 0.25 x 0.75 = 0.1875
• Cl-37, Cl-37 = 0.25 x 0.25 = 0.0625
2) Cl-35, Cl-37 is the same as Cl-37, Cl-35. So Cl-35, Cl-37 = 0.1875 + 0.1875 = 0.375
3) Smallest abundance = 0.0625
• Cl-35, Cl-35 -> 0.5625 / 0.0625 = 9 (Mr = 70)
• Cl-35, Cl-37 -> 0.375 / 0.0625 = 6 (Mr = 72)
• Cl-37, Cl-37 -> 0.0625 / 0.0625 = 1 (Mr = 74)
4) Draw the graph of relative abundance against m/z.
(See diagram pg 8 of revision guide)
How can the mass spectrum of a molecule be used to identify its Mr?
By looking at the m/z value of the peak with the highest m/z.
(NOTE: Ignore any very small peaks above this - due to carbon-13)
During mass spectrometry, when the molecules in a sample are bombarded with electrons, what is formed?
A molecular ion (M+).
When identifying the Mr of a molecule by its mass spectrum, why are there very small peaks after the M+ peak and why can they be ignored?
These are caused by the presence of carbon-13 atoms and are uncommon.
When looking at a mass spectrum for an unknown alcohol, how would you identify the alcohol?
- Look at the peak with the highest m/z value (ignoring any tiny peaks after it)
- The m/z value is the Mr of the alcohol
- Calculate the Mr of the first few alcohols until you find the corresponding alcohol
Explain how mass spectrometry works.
1) Ionisation - The substance is bombarded with electrons, which knock out electrons to form positive ions
2) Acceleration - The ions are accelerated through an electric field.
3) Deflection - A magnetic field deflects the ions by different amounts according to their mass to charge ratio.
4) Detection - The number of ions arriving at each m/z value is detected by a computer.
What are some uses of mass spectrometry?
Used to analyse samples in: • Radioactive dating • Space research • Detection of illegal drugs in sport • Pharmaceutical industry
Remember to revise mass spectra.
Pg 7 + 9 of revision guide
Describe the idea of electronic structure.
- Electrons move around in quantum shells -> e.g. 2nd shell
- The shells contain different types of subshell -> e.g. 2nd shell contains 2s and 2p subshell
- Each subshell has a different number of orbitals, which can each hold 2 electrons -> e.g. 2p subshell has 3 orbitals, so 6 electrons
- Shells/Energy levels -> Subshells -> Orbitals
What is the numbering of quantum shells called?
They are given numbers called “principal quantum numbers”.
What are quantum shells also known as?
Energy levels
How are the shells numbered?
The further from the nucleus, the greater the energy level, starting at 1.
How many electrons can an orbital hold?
2
What are the four subshells?
s, p, d, f
How many orbitals and electrons in an ‘s’ subshell?
Orbitals: 1
Max. electrons: 2
How many orbitals and electrons in a ‘p’ subshell?
Orbitals: 3
Max. electrons: 6
How many orbitals and electrons in a ‘d’ subshell?
Orbitals: 5
Max. electrons: 10
How many orbitals and electrons in an ‘f’ subshell?
Orbitals: 7
Max. electrons: 14
Name the four subshells and the number of electrons in each.
- s - 2
- p - 6
- d - 10
- f - 14
Name the subshells in the 1st energy level.
1s
Name the subshells in the 2nd energy level.
2s 2p
Name the subshells in the 3rd energy level.
3s 3p 3d
Name the subshells in the 4th energy level.
4s 4p 4d 4f