atomic structure Flashcards
What is the atomic number
The number of protons, it defines the element
What is the mass number
The protons and the neutrons
How do you calculate the neutrons
Mass number - proton number
What is the Bohr model
Atoms are made of three subatomic particles, protons, neutrons & electrons
E-s in shells surrounding the nucleus
Protons & neutrons in the nucleus
What is the relative mass & charge of the following
Proton
Neutron
Electron
Proton - 1, +1
Neutron- 1, 0
Electron - 1/1840, -1
Define isotope
Same number of protons, different number of neutrons
What are the chemical properties of isotopes
Isotopes have the same chemical properties
Because they have the same electronic configuration
What evidence was found to support Rutherfords model
Most of the alpha particles passed straight through the gold foil
Atoms are mainly empty space
Small number of particles bounced back
Atoms have a smalls positive nucleus
What are the key differences between Thompson’s model & Bohr’ model
Bohr model has e’s surrounding nucleus in shells
Small positive nucleus
Define ionisation energy
The amount of energy required to remove one mole of electron (E-s) from one mole of atoms in gaseous state
Give the first 3 ionisation energy of Na
Na (g) -> Na+ (g) + E-
Na+ (g) -> Na2+ (g) + E-
Na2+ (g) -> Na3+ + E-
What are the 3 factors that will influence ionisation energy
Nuclear charge, amount of protons-
More protons means a stronger attraction between the nucleus and the outer e-s
More energy is needed to remove the outer e-
Distance from the nucleus-
Outer e- is closed it the nucleus
Means there is a stronger attraction between the outer e- and nucleus
More energy needed to remove outer e-
Shielding -
More shielding
Weaker attraction between outer e- and the nucleus
Less energy needed to remove the outer e-
CONSIDER SHIELDING FIRST
What are the trends in the first IE across a period
Increases across a period
Atomic radius decreases across a period
Some shielding
Increases protons -> increasing attraction between protons & outer e-s
What is the electronic configuration for chromium
1s2, 2s2, 2p6,3s2,3p6,4s1, 3d5
What is the electronic configuration for copper
1s2, 2s2, 2p6,3s2,3p6,4s1, 3d10
Trends in ionisation energies across period 2
General increase in 1st IE
Shielding is the same for all atoms
Number of protons increase - increasing attraction between outer e- and nucleus
Trends in ionisation energies in period 3
General increase in 1st IE
Shielding is the same for all atoms
Number of protons increase - increasing attraction between outer e- and nucleus
How does ionisation energy change down a group
IE decreases down groups because
Atomic radius increases
Shielding increases
Outer e-s less attracted to nucleus
State and explain the trend is atomic radius down a group
Atomic radius increases
Shielding increases
Outer e-s less attracted to nucleus
Why does atomic radius get smaller from right to left across a period
Shielding stays the same
Number of protons increases
Outer electrons are more attracted to the nucleus
How can time of flight be measured
T = d/v
T = d square root m/2KE
What does KE equal
What does m equal
What does v2 equal
KE + 1/2 mv^2
M = KE / 1/2 v2
V2 = square root KE/ 1/2 m
What two factors does the mass spectrometer measure
Relative abundance
Mass/charge ratio (m/z)
Why are the sample particles ionised?
• So they can be accelerated towards the negatively charged plate
• So they generate a current when they hit the detector
How is the ion accelerated?
•Positive ions attracted to the negatively charged plate
• All ions have the same kinetic energy
How are ions separated in the flight tube?
• lons travelling at higher speeds (small m/z) move ahead of those travelling more slowly (large m/z)
How are the ions detected?
• Each ions hits the detector
• Ion gains an electron
• Generates a current
• Size of the current is proportional to the abundance of the ion
What is the formula for electron impact
X(g) —> X+ (g) + e-
What is the equation for electro spray ionisation
H+ —> XH+
Describe electrospray ionisation
The sample X is dissolved in a volatile solvent (eg water or methanol) and injected through a fine hypodermic needle to give a fine mist (aerosol). The tip of the needle is attached to the positive terminal of a high-voltage power supply.
The particles are ionised by gaining a proton (ie an H + ion which is simply one proton) from the solvent as they leave the needle producing XH* ions (ions with a single positive charge and a mass of Mr + 1).
Describe electron impact
The sample being analysed is vaporised and then high energy electrons are fired at it.
The high energy electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons.
This usually knocks off one electron from each particle forming a 1+ ion
