Questions and Answers
What is the physical state of argon at room temperature?
What is the general trend of first ionisation energies across period 3?
Why do aluminium and sulfur not follow the general trend of first ionisation energies?
What happens to the electrons between magnesium and aluminium?
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Why can an electron be removed more easily between magnesium and aluminium?
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What happens to the electrons between phosphorus and sulfur?
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Why can an electron be removed with less energy than expected between phosphorus and sulfur?
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What is the result of the decreasing atomic radius and increasing nuclear charge across period 3?
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What is the energy level of the 3p orbital compared to the 3s orbital?
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Why do electrons in the 3p orbital have a slightly higher energy level?
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Study Notes
Atomic Structure
- Atomic number and mass number can be used to calculate the number of protons, electrons, and neutrons in an atom
- Number of protons = atomic number
- Number of electrons = atomic number
- Number of neutrons = mass number - atomic number
Isotopes
- Atoms of the same element with the same atomic number but different number of neutrons
- Result in different mass numbers and physical properties
- Neutral atoms of isotopes react chemically in the same way due to same proton number and electron configuration
- Example: Hydrogen, Deuterium, and Tritium are isotopes of hydrogen
Relative Masses
- Relative atomic mass (Ar) is the mean mass of an atom of an element relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
- Takes into account the relative abundances of different isotopes of an element
- Relative isotopic mass is the isotopic mass of an isotope relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
- Relative molecular mass (Mr) is the mean mass of a molecule of a compound relative to one twelfth of the mean mass of an atom of the carbon-12 isotope
- Can be calculated by adding together the separate Ar values of the component elements
Ions and Mass Spectrometry
- Ions are formed when an atom loses or gains electrons, resulting in an overall charge
- Useful in mass spectrometry to identify different isotopes and find the overall relative atomic mass of an element
- Time of Flight (TOF) Mass Spectrometry:
- Ionisation: vapourised sample is ionised, leaving +1 charged ions
- Acceleration: positively charged ions are accelerated towards a negatively charged detection plate
- Ion Drift: ions are deflected by a magnetic field into a curved path dependent on charge and mass
- Detection: ions hit the detection plate, producing a flow of charge
- Analysis: current values are used to produce a spectra print-out with relative abundance of each isotope
Predicting Mass Spectra
- If you know the abundances of an isotope, you can generate the mass spectra for its molecules, including relative peak heights
- Example: calculating Ar (relative atomic mass) from mass spectra can help identify the element by referring to the Periodic Table
Ionisation Energy
- Increases along a period due to decreasing atomic radius and increasing nuclear charge
- Decreases down a group due to decreasing nuclear attraction and increasing shielding
- Physical Properties of Period 2:
- Melting points peak towards the middle of the period due to different bond strength and structures
- Ionisation energies follow a general increasing trend along period 2 due to decreasing atomic radius and increasing nuclear charge
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Description
This quiz helps you understand how to calculate the number of protons, neutrons, and electrons in an atom using atomic number and mass number. Test your knowledge of atomic structure!
