Atomic Structure and Mass Spectrometry Concepts

What are the three subatomic particles that make up an atom?

Protons, neutrons, and electrons.

Where are electrons located in an atom?

Electrons are found surrounding the nucleus in orbitals.

What holds protons and neutrons together in the nucleus?

A strong nuclear force.

What type of force holds electrons in their orbitals around the nucleus?

Electrostatic forces between protons and electrons.

Who proposed that atoms are solid spheres that make up elements?

John Dalton.

What model did J.J. Thomson propose regarding atomic structure?

The plum pudding model, which showed that atoms contain electrons.

What significant experiment did Ernest Rutherford conduct, and what was its outcome?

He conducted the alpha scattering gold foil experiment, which showed that most of the atom is empty space with a positive center.

How did Niels Bohr adapt the nuclear model of the atom?

He placed electrons in shells/orbitals of fixed energy.

What happens when electrons move to a new shell in an atom?

Electromagnetic radiation is emitted or absorbed.

What is the mass number (A) of an atom?

The total number of protons and neutrons in the nucleus.

What is the atomic number (Z) of an atom?

The number of protons in the nucleus, which also equals the number of electrons.

What does relative atomic mass (Ar) represent?

The average mass of an atom of an element, considering its isotopes, relative to 1/12th the mass of carbon-12.

What is the formula for calculating relative atomic mass (Ar)?

Ar = (isotope mass number x % abundance) + (isotope mass number x % abundance) ... divided by the sum of % isotope abundance.

What is the difference between relative isotopic mass and relative atomic mass?

Relative isotopic mass is the mass of an atom of an isotope relative to carbon-12 and is always a whole number.

What is relative molecular mass (Mr)?

The average mass of a molecule in relation to 1/12th the mass of a carbon-12 atom.

What defines an isotope?

An isotope is an atom of the same element with the same number of protons but a different number of neutrons.

How do isotopes of the same element compare in terms of chemical properties?

Isotopes have the same chemical properties due to the same electron configuration.

What physical property differences can isotopes exhibit?

Isotopes can have slightly different physical properties, such as density.

What is the significance of the number of electrons in the outer shell of an atom?

It determines the chemical properties of the element and how it reacts.

What is the relationship between atomic number and chemical identity?

All atoms of the same element have the same atomic number, which defines their chemical identity.

What did scientists realize about electrons in the same shell?

Not all electrons in the same shell have the same energy, leading to the refinement of atomic models to include subshells.

What was the main conclusion of Rutherford's gold foil experiment?

Most alpha particles passed straight through the foil, indicating that atoms are mostly empty space.

What makes an isotope radioactive?

An isotope can be radioactive if it is unstable, which is caused by having extra protons or neutrons in the nucleus that create extra energy.

How is the rate of radioactive decay measured?

The rate of radioactive decay is measured by half-life, which is the time it takes for half of its radioactivity to decay.

What is carbon dating and which isotope is used for it?

Carbon dating is a method used to determine the age of living organisms using the radioactive isotope Carbon-14, which has a long half-life.

What is a Time of Flight Mass Spectrometer (TOFMS)?

TOFMS is a powerful instrumental technique used for the accurate determination of relative isotopic masses and relative abundances of atoms/molecules.

What are the main stages of TOFMS?

The main stages of TOFMS are Ionisation, Acceleration, Ion Drift, Detection, and Data Analysis.

What occurs during the ionisation stage of TOFMS?

In the ionisation stage, each atom becomes an ion, which can occur through Electron Impact Ionisation or Electrospray Ionisation.

Describe Electron Impact Ionisation.

Electron Impact Ionisation is used for compounds with low molecular mass, where high energy electrons are fired at a vaporised sample, knocking off an electron to form a 1+ ion.

Describe Electrospray Ionisation.

Electrospray Ionisation is used for compounds with high relative molecular mass, where the sample is dissolved in a volatile solvent and injected into the ionisation chamber, gaining a proton to become a 1+ ion.

What happens during the acceleration stage of TOFMS?

Ions are accelerated using an electric field towards a negatively charged plate, ensuring they all have the same kinetic energy, although their velocities differ based on mass.

What occurs during the ion drift stage of TOFMS?

Ions pass through a hole into the flight tube where they drift through a region with no electric field, with different masses resulting in different times of flight.

How is detection achieved in TOFMS?

Detection occurs when ions hit a negatively charged plate, producing a current as positive ions pick up an electron from the detector.

What does the mass spectrum of an element show?

The mass spectrum shows the mass:charge ratio (same as mass number for 1+ charge) on the x-axis and the relative % abundance of each isotope on the y-axis.

How can mass spectra be used to determine relative atomic mass?

Mass spectra can be used to calculate the relative atomic mass of an element to up to 5 decimal places using high resolution mass spectrometry.

What is indicated by the main peak on a mass spectrum?

The main peak on a mass spectrum indicates the molecular mass [Mr], which is the highest, furthest right, and most abundant peak.

How can isotopes be identified using mass spectra?

Each isotope produces a line on the spectra corresponding to its different mass, and a + is placed after the isotope when identifying which reaches the detector first.

What is the significance of the current produced in the detection stage?

The current produced in the detection stage indicates the presence of ions hitting the detector plate, which is essential for generating the mass spectrum.

What is the role of data analysis in TOFMS?

signal passed from detector to computer which generates a mass spectrum for interpretation

What is the relationship between mass number and charge in mass spectra?

Most isotopes have a 1+ charge, making the mass:charge ratio equivalent to the mass number.

What is the purpose of using TOFMS in forensic science?

TOFMS is used by forensic scientists to accurately identify illegal drugs by determining the masses and relative abundances of the components.

Why must samples be in a gaseous state for TOFMS?

Samples must be in a gaseous state to allow for effective ionisation and separation based on mass during the TOFMS process.

What is the difference between high resolution and low resolution mass spectrometry?

High resolution mass spectrometry can determine relative atomic mass up to 5 decimal places, while low resolution mass spectrometry typically does so to 1 decimal place.

What happens to the ions after they are detected in TOFMS?

After detection, the ions produce a current that is analyzed to create a mass spectrum, which provides information about the isotopes present.

What is the relationship between the Mr and the highest peak in electrospray mass spectrometry?

The Mr is always 1 less than the highest peak.

What causes the peak at Mr+1 in mass spectra of organic compounds?

It is due to isotopes of carbon (13C) and hydrogen (2H).

What are single isotope peaks in mass spectrometry?

They are peaks at the mass of the isotopes, representing mononuclear ions forming monatomic fragments.

What happens to molecular ions during fragmentation in mass spectrometry?

They break into smaller particles, resulting in smaller ions or free radicals.

What is the m/z ratio for the mononuclear ion of chlorine?

The m/z ratio is 35.

What is the m/z ratio for the molecular ion of chlorine?

The m/z ratio is 70.

What is the ratio of isotopes for chlorine in mass spectrometry?

35Cl is 75% and 37Cl is 25%, resulting in a 3:1 ratio.

What is the calculated ratio of peaks at m/z 70, 72, and 74 for chlorine isotopes?

The ratio is 9:6:1.

What is the formula for calculating the mass of one ion in kg?

M = mass in kg, using the relative atomic mass (Ar) and Avogadro's constant.

How is the kinetic energy of one ion calculated?

Using the rearranged kinetic energy equation, substituting velocity (V) for distance (d) over time (t).

What is the relationship between the time of flight (TOF) of two ions with the same kinetic energy?

The TOF is inversely proportional to the square root of their masses.

What principle states that electrons fill the lowest energy subshells first?

The Aufbau principle.

What is Hund's rule in electron configuration?

Electrons fill orbitals singularly before they start sharing.

What is the maximum number of electrons in the s subshell?

2 electrons.

What is the maximum number of electrons in the p subshell?

6 electrons.

What is the maximum number of electrons in the d subshell?

10 electrons.

What is the maximum number of electrons in the f subshell?

14 electrons.

How can electron configurations be written in shorthand?

By using the symbol of the last noble gas before the element and adding the extra electrons in subshells.

What is the total number of electrons in the 3rd energy level?

18 electrons.

What is the total number of electrons in the 4th energy level?

31 electrons.

What is the significance of the 4s subshell in relation to the 3d subshell?

The 4s subshell has a lower energy than the 3d subshell, so it fills up first.

What is the role of Avogadro's constant in mass spectrometry calculations?

It is used to convert the mass of one ion into kg for calculations.

What is the electron configuration of Chromium?

1s2 2s2 2p6 3s2 3p6 4s1 3d5, due to the donation of one 4s electron to the 3d subshell for stability.

What is the electron configuration of Copper?

1s2 2s2 2p6 3s2 3p6 4s1 3d10, due to the donation of one 4s electron to the 3d subshell for stability.

What is the order of electron loss when forming cations?

The 4s electrons are lost before the 3d electrons.

Define first ionization energy.

The energy needed to remove one electron from each atom of an element in one mole of gaseous atoms to form one mole of gaseous ions with a 1+ charge.

Define second ionization energy.

The energy needed to remove one electron from each ion of an element in one mole of gaseous +1 ions to form one mole of gaseous ions with a +2 charge.

How does atomic radius affect ionization energy?

The smaller the atomic radius, the higher the first ionization energy, as the outer electron is more strongly attracted to the nucleus.

How does nuclear charge affect ionization energy?

A higher nuclear charge results in a higher first ionization energy, as there are more protons to attract the outer electrons, leading to a smaller atomic radius.

What is the effect of shielding on ionization energy?

More shielding lowers the first ionization energy because inner shells repel outer electrons, making them easier to lose.

What is the trend in ionization energy across a period?

Ionization energy increases across a period due to higher nuclear charge and smaller atomic radius, with constant shielding.

What is the trend in ionization energy down a group?

Ionization energy decreases down a group due to larger atomic radius and increased shielding, making outer electrons easier to lose.

What is the exception in ionization energy between Group 2 and 3?

There is a dip in first ionization energy due to moving to a new energy level with higher energy (S to P subshell), resulting in more shielding.

What is the exception in ionization energy between Group 5 and 6?

There is a dip in first ionization energy because in Group 5, the p subshell has one electron in each orbital, while in Group 6, one orbital has two electrons, leading to repulsion.

What are successive ionization energies?

Successive ionization energies refer to the energy required to remove additional electrons from an increasingly positive ion, which increases as more electrons are removed.

Why do successive ionization energies increase between shells?

There is a sudden rise in ionization energy when a new shell is broken into, as the next electron is removed from a shell closer to the nucleus.

How do successive ionization energies increase within each shell?

Each time an electron is removed, the ion becomes more positive, increasing the attraction from the nucleus and thus requiring more energy to remove the next electron.

What evidence supports the shell structure of atoms?

A sudden jump in ionization energy indicates that another shell has been entered, such as the drop in first ionization energy between Group 2 and 3.