Atomic Structure and the Periodic Table Flashcards
What is atomic number (Z)
The number of protons in the nucleus of an atom of an element
What is the mass number of an element
is the sum of the number of protons and the number of neutrons in the nucleus of an atom
What is an isotope
Are atoms of the same element witht the same number of protons but a different mass number due to a different number of protons
What is the symbol,
relative mass/charge
and position in atoms of a
Proton
p
1
+1
nucleus
What is the symbol,
relative mass/charge
and position in atoms of a
Neutrons
n
1
0
nucleus
What is the symbol,
relative mass/charge
and position in atoms of a
Electron
e-
1/1840
-1
energy levels surrounding the nucleus
Relative atomic mass (Ar)
The weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12
Relative isotopic mass
The mass of an individual atom of a particular isotope relative to 1/12 of the mass of an atom of carbon-12
What does a mass spectrometer do
How does it work
measures the mases of atoms and molecules
Produces positive ions, which are deflected by a magnetic feild, according to the m/z ratio
It also calculates relative abundance in %
Why are mass spectrometers important in terms of isotopes
determine the exact values of relative masses of isotopes
As well as the % abundance
This information can be used to calculate relative atomic mass
How can the relative molecular mass of diatomic molecules be measured
In a mass spectrometer
you can obtain Mr of element/compound by observing peaks with largest m/z ratio
What is the molecular ion peak
the peak with the highest m/z ratio in the mass spectrum
M peak
How would you work out the number of neutrons from atomic (z) and mass numbers
mass number - atomic number = neutrons
How can you work out mass number?
atomic (protons z) + neutrons = mass number
What would the mass spectrometry look like for chlorine and why?
3:1 ratio for Chlorine 35 and 37
Then a 9:6:1 ratio at 70,72,74 due to Chlorine being diatomic.
(35+35=70) (35+37=72) (37+37=74)
Why is there a 9:6:1 ratio with peaks at 70, 72 and 74 on the chlorine mass spectrometry
It is a 3:4 ratio for Chlorine 35 and 37
(35+35) 70: 3/4 x 3/4 = 9/16
(35+37) 72: 3/4 x 1/4 = 3/16
(37+37) 74: 1/4 x 1/4 = 1/16
9:6:1
What would the mass spectrometry look like for bromine and why
(two isotopes are 79 and 81)
two peaks at 79 and 81 at equal heights at a 1:1 ratio
(79+79) = 158: 1/2 x 1/2 = 1/4
(79+81) = 160: 2(1/2 x 1/2) = 2/4
(81+81) = 162: 1/2 x 1/2 = 1/4
1:2:1
How do you work out relative atomic mass from relative isotopic mass and percentage abundance on a mass spectrometer
(relative isotopic mass x percentage abundace) / 100
Work out the relative atomic mass of lithium when 7.59% of the sample has 6.015 isotopic mass and 92.41% has a 7.016 isotopic mass
(6.015 x 7.59) + (7.016 x 92.41) / 100
= 6.94
What is the molecular ion peak
is the peak with the highest m/z ratio on the spectrum (M)
How would you work out the relative molecular mass of Chlorine, when you have 9:6:1 ratio of peaks at 70,72,42
(9 x 70) + (6 x 72) + (1 x 74) / 16
= 71
What is a quantum shell
defines the energy level of an electron
What is an orbital
is a region within an atom that can hold up to two electrons with opposite spins
What is electron configuration
shows the number of electrons in each sublevel in each energy level of an atom
What is Hund’s rule
states that electrons will occupy the orbitals singly before pairing takes place
What is the Pauli Exclusion Principle
states that two electrons cannot occupy the same orbital unless they have opposite spins. Electrons spins are shown by single-headed arrows in opposite directions
What are the 4 quantum shell and how many electrons can go in each
S = 2 (1 x 2)
P = 6 (3 x 2)
D = 10 (5 x 2)
F = 14 (7 x 2)
x 2 because each orbital can hold 2 electrons
What is the shape of the S orbital
What is the shape of the P orbital
How many electrons can fill the first 4 quantum shells
1st : 2 (1s²)
2nd : 8 (2s² 2p6)
3rd: 18 (3s² 3p6 3d10)
4th: 32 (4s² 4p6 4d10 4f14)
What is the exceptions to the allocation of electrons in the electron configuration
the 4s has a lower energy level than the 3d shell therefore the 4s shell fills before the 3d shell does
How do you configure electrons in boxes
an electron will fill an orbital singly before pairing takes place
only two electrons can occupy and orbital with opposite spins
What is the first ionisation energy
is the energy required to remove an electron from each atom in one mole of atoms in gaseous state
What is second ionisation energies
is the energy required to remove an electron from each singly charged positive ion in one mole of positive ions in gaseous state
How can we signify first ionisation energy of element A
A(g) + A+(g) + e-
How can we signify second ionisation energy
A+(g) → A2+(g) + e-
Where did evidence for different energy levels initially come from
atomic emission spectra
Heating atoms in gaseous state, moving electrons to a higher energy level. When they return back they release EM radiation.
There are many specific frequencies produced per element, indicating it requires a different amount of energy to remove electrons
How can you tell what group an element is in by looking at its ionisation energies
big jumps in energies is a piece of evidence for quantum shells
How can you tell where groups occur on a logarithm for successive ionisation for Sodium
quantum shell configuration: 2, 8, 1
Jump from 1st to 2nd, due to the outer electron being removed from the highest energy level of the third quantum
Jump from 9th to 10th, due to movement from the 2nd energy level to the first
Why do successive ionisation energies increase in magnitude
The first electron lost during ionisation is furthest from the influence of the nucleus
Out electrons also exits in high energy levels, so will require little to remove it
What is the equation for working out ionisation energy (IE)
IE = energy of electron when removed - energy of electron when in orbital
When does electron-electron repulsion occur
- two electrons in the same orbital
- electrons in different orbitals in a quantum shell
- Electrons in adjacent quantum shells
Which first ionisation energy will be the largest in Hydrogen or Helium
Hydrogen(1s1)
Helium (1s2)
Outer electrons are in the same orbital
However, helium contains 2 electrons, increasing electron-electron repulsion - each electron is said to shield one another from nuclear charge
Nuclear charge of helium is double that of hydrogen
Effect of nuclear charge us greater than shielding, so helium has a higher ionisation energy
Which ionisation energy is greater, Helium or lithium
Helium (1s2)
Lithium (1s2 2s1)
Lithium has a greater nuclear charge
Lithium’s outer electron is in the 2s orbital, being in the second quantum shell, having a higher energy level. Therefore lower ionisation energy
Will also experience electron-electron repulsion from the 1s orbital
So Helium has a higher ionisation energy
What effect the energy the electron has, hence the first ionisation energy
- Orbital the electron exists within
- Nuclear charge of the atom (no of protons)
- Repulsion (shielding) experienced by electrons from all other electrons present
What is the trend in ionisation energies across a period and why
From (Li to Ne) period 2
Nuclear charge will increase, as a proton will be added each time
However, one more electron is also added to same quantum shell, increasing electron-electron repulsion
Increase in nuclear charge is greater than that of electron repulsion, so first ionisation energy increases across period 2
Trend in ionsation energy down a group and why
(Li to Cs) group 1
Nuclear charge increase, as number of protons increases meaning increased attraction with nucleus - increase in ionisation energies
However, new quantum shell is added, each occasion, which has a higher energy level and increases electron-electron repulsion between shells
Therefore, first ionisation energy decreases down the group
Why do elements within groups have similar chemical properties
same outer electron confirguration
All elements in a main group, contain the same electron configuration
If n = the period
Write the electron configuration for groups 1-8
Group 1 : ns1
Group 2 : ns2
Group 3 : ns2 np1
Group 4 : ns2 np2
Group 5 : ns2 np3
Group 6 : ns2 np4
Group 7 : ns2 np5
Group 8 : ns2 np6
Which groups of the periodic table does the S block contain
Groups 1 and 2
Which groups of the periodic table does P-block contain
Groups 3-8
What elements are contained within d-block
Transition metals
Period 4 (Sc to Zn)
Period 5 (Y to Cd)
Defintion of peridicitiy
is a regularly repeating pattern of atomic, physical and chemical properties with increasing atomic number
What is the trend across the periodic table for size of nucleus
Size of radius decrease across each period
This is because the number of protons increases, increasing attractive forces between outer electrons
Although is offset through electron-electron repulsion as an electron is added each time
What is the trend in melting temperatures across period two
Increase from Li to C
Due to molecules being more charged
Decrease from N2 to F2 because they exist as simple molecular diatomic molecules
What is the trend in boiling temperature across group 2
Increase from Li to C
Due to more charged molecules and moving from metallic to covalent bonding
Decrease from N2 to F2 due to simple molecular diatomic covalent bonding
What is the trend with boiling and melting temperatures across period 3
Increase from Na to Si
Due to increase in charge and moving from metallic giant lattices to covalent giant lattices
Then a decrease from P2 to Cl2 due to simple molecular covalent bonding
Describe the graph for first ionisation energies for the first 3 periods
First ionsation energies highest for Nobel Gases (He, Ne, Ar)
Lowest for group one elements (Li and Na)
Anomaly increase at Helium
Group 2 (ns2) and group 3 (ns2 np1) the np1 in group 3 increases increases electron-electron repulsion therefore group 3 has lower ionisation energies than group 2
Why do nitrogen and oxygen have an anomaly when calculating ionisation energies
N: 1s2 2s2 2p3
O: 1s2 2s2 2p4
First electron removed from Oxygen is paired, which has increased electron-electron repulsion
Less energy is required to remove the first electron because it is the same quantum shell and energy level
