Atomic Structure Flashcards
Name the three types of particle in an atom. State the relative mass and charge of each particle.
Protons: Mass 1, Charge +1
Neutrons: Mass 1, Charge 0
Electrons: Mass 1/1840, Charge -1
How are the particles in an atom arranged?
Protons and neutrons in central nucleus held by strong nuclear force. Electrons orbit nucleus in shells (electrostatic force).
How many electrons do the first shells hold?
1st Shell = 2
2nd Shell = 8
3rd Shell = 18
Define the term mass number, A.
The total number of protons and neutrons in the nucleus of the atom
Define the term atomic number, Z.
The number of protons in the nucleus. This defines the atom and is used to order elements in the periodic table. By default, in a neutral atom, this also happens
to be the number of electrons.
Define the term Isotope
Atoms with the same number of protons but different numbers of neutrons.
Why do isotopes of the same element have identical chemical properties?
They have the same number and arrangement of electrons.
What does a mass spectrometer measure?
Relative atomic masses
Relative molecular masses
Describe how a mass spectrometer works (the 6 stages).
The instrument is kept under a high vacuum so that the ions do not collide with air molecules.
●Vaporisation - sample injected into instrument if gaseous or volatile liquid, if solid is vaporised by heating
●Ionisation - sample is passed through stream of high energy electrons from a beam of electrons from electron gun knocks out electrons to form positive ions. Nearly all atoms or molecules lose just one electron and form ions with a 1+ charge but a small number (typically around 5%) lose two electrons to form ions with a 2 + charge
●Acceleration - positive ions are attracted towards negatively charged plates and are accelerated to high speed.
●Deflection - Magnetic field deflects beam into an arc circle. Heavier ions are deflected less and 2+ ions are deflected twice as much as 1+ ions with same mass. Stronger field, greater deflection.
●Detection - magnetic field is gradually increased so that ions of increasing mass enter detector one after another. Ions strike detector, and create a current which is proportional to the abundance of each ion. From strength of magnetic field at which a particular ion hits detector, a computer works out value of charge ratio of original ion
Write down the sub-shells in order of increasing energy up to 4f?
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶4d¹⁰4f¹⁴
Which are the two anomalies involving electronic structure? Why?
Chromium (Cr) and Copper (Cu)
They donate one of their 4s electrons to the 3d sub-shell (they only have one 4s electron
Define the term first ionisation energy (IE).
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous positive ions
Label axis for spectrometer graph.
Y axis - Abundance (%)
X axis - Mass:Charge ratio (m/z)
Give an equation to work out Mr from a mass spectrometer reading.
Mr = Total of (m/z x abundance) / total abundance
Define 2nd ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous 1+ ions
Electrospray ionisation is the first step of mass spectrometry. What does it involve?
A dissolved sample is forced through a fine needle that is connected to the positive terminal of a high voltage supply. The sample loses electrons, forming positive ions. (high voltage knocks electron off sample)
What happens in the acceleration area of a mass spectrometer?
Negatively charged plates attracts and accelerates ions to the same kinetic energy. The lighter ions accelerate more as they are lighter.
What is the role of an ion detector in a mass spectrometer?
When positive ions his the ion detector, they pick up an electron, causing a current to flow. A flight time can also be detected
What four stages occur in mass spectrometry?
- Ionisation
- Acceleration
- Deflection
- Detection
Define Relative Atomic Mass
The average mass of all isotopes of an element compared to 1/12 the mass of a carbon-12 atom.
Mass Spectrometer: What happens during ionisation?
The sample is dissolved in a volatile solvent and forced through a fine, hollow needle which is connected to a positive terminal of a high voltage supply. The sample is shot with an electron gun, which knocks off an electron, producing positively charged ions.
Mass Spectrometer: What happens during acceleration?
Positive ions are attracted to a negatively charged plate, causing them to accelerate. Lighter ions with a higher charge move faster
Mass Spectrometer: What happens during ion drift?
The ions pass through a hole in the negatively charged plate, forming a beam, which drift towards the detector
Mass Spectrometer: What happens during detection?
The lighter ions which have the fastest velocities arrive at the detector first. The positive ions pick up an electron, causing a current to flow
Mass Spectrometer: What happens during data analysis?
Signals from the detector are passed to a computer which generates a mass spectrum
Factors affect ionisation energy: Nuclear Charge
The higher the nuclear charge (the more protons there are) the greater the attraction of the outer electrons to the nucleus
Factors affect ionisation energy: The distance of the outer electrons to the nucleus
The larger the atom, the further the outer electrons are away from the nucleus, making the attraction weaker
Factors affect ionisation energy: Shielding
Electrons in the outer shell are repelled by electrons in complete inner shells, weakening the attraction of the nucleus
Why are the successive ionisation energies always higher?
Because a positive ion is formed from the first ionisation energy, meaning the nuclear attraction increases, making it harder for the second electron to be removed
What was the Plum Pudding Model?
Thought that atoms consisted of a sphere of positive charge
What is the electron shell model?
Atoms consist of a small dense central nucleus surrounded by orbiting electrons in electron shells. This was discovered by Rutherford scattering experiment in 1911
What did the Rutherford scattering experiment show?
The nucleus consists of protons and neutrons giving it an overall positive charge. It contains almost the entire of mass of the atom. In a neutral atom, the number of electrons is equal to the number of protons due to relative charges
Give the relative charge and the relative mass of a proton
Relative charge: +1
Relative Mass: 1
Give the relative charge and the relative mass of a neutron?
Relative charge: 0
Relative Mass: 1
Give the relative charge and the relative mass of an electron
Relative charge: -1
Relative mass: 1/1840
What does the maximum number of orbiting electrons that can be held by any single cell depend on?
The number of the shell.
This can be calculated by 2n^2 where n is the number of the shell
What shape does a s-orbital have?
spherical
What shape does a p-orbital have?
dumbell
Why do electrons pair up with opposite spin?
So that the atom is as stable as possible. Electrons in the same orbital must have opposite spin
How is a spin represented?
with an arrow
What are the rules for writing out electron configurations?
- The lowest energy orbital is filled first
- Electrons with the same spin fill up an orbital before pairing begins
- No single orbital holds more than 2 electrons
What are the exceptions to the rules?
If electron spins are unpaired and therefore unbalanced, it produces a natural repulsion between the electrons making atom very unstable
The electrons may take on a different arrangement to improve stability
When does successive ionisation energy occur?
When further electrons are removed
Why does successive ionisation energy require more energy?
Because as electrons are removed the electrostatic force of attraction between the positive nucleus and the negative outer electrons increases. More energy is needed to overcome this attraction so ionisation energy increases
What trends do first ionisation energies follow within the periodic table going along a period?
Along a period - 1st ionisation energy increases due to an increasing atomic radius and greater electrostatic forces of attraction
What trends do first ionisation energies follow within the periodic table when going down a group?
1st ionisation energy decreases due to an increasing atomic radius and shielding which reduces the effect of the electrostatic forces of attraction
When successive ionisation energies are plotted on a graph what does a sudden large increase indicate? Why?
A change in energy level
Because the electron is being removed from an orbital closer to the nucleus so more energy is required to do so
What does large energy increases provide supporting evidence for?
The atomic orbital theory
