Atomic Structure Flashcards
What is the top number when representing an element?
Mass number/nucleon number
What is nucleon number/mass number?
Total number of protons and neutrons in the nucleus of an atom
What is the bottom number when representing an element?
Atomic number/proton number?
What is atomic number/proton number?
number of protons in the nucleus of an atom
What is the characteristics of an atom?
It is electrically neutral, it has the same number of electrons and protons
What are isotopes?
Atoms of the same element with the same number of protons but different number of neutrons
What are isotopes of the same element similar in?
- Number of electrons
- Number of protons/ Atomic number
- Chemical Properties
What do isotopes of the same element differ in?
- Number of neutrons
- Mass number
- Relative atomic mass
- Physical properties
What is isotopic?
Atoms or ions that contain the same number of protons
What is isoelectronic?
Atoms or ions that contain the same number of electrons
What is isotonic?
Atoms or ions that contain the same number of neutrons
What is the extent of deflection directly proportional to?
Charge/mass where the mass is the mass number
What happens to the extent of deflection when the charge is greater?
When the charge is greater, the extent of deflection is greater because of the stronger electrostatic forces of attraction that pulls it downwards/upwards towards the charge plate
What happens to the extent of deflection when the mass is greater?
The extent of deflection is smaller because the heavier ion have larger inertia and is harder to pull it downwards to the negatively charged plate
What is an orbital?
A region of space where there is a high probability density or electron density
What is the chance of finding an electron in an orbital?
95%
What are the characteristics of s orbital?
- Each s subshell contains only one orbital
- Spherical shape
- Non-directional nature
- Equal probability of finding an electron at any given distance
- 0 probability at the nucleus
What are the characteristics of p orbital?
- each p subshell has 3 degenerate orbitals (px, py, pz)
- dumbbell shape
- symmetrical along axis
- directional nature
- 0 probability at the nucleus
What are the characteristics of d orbital?
- each d subshell has 5 degenerate orbitals
- gives transitional metals their special properties
- 0 probability of finding an electron along dxy, dxz, dyz axes
What is the maximum number of electrons each orbital can accommodate?
2
What happens to the size of the orbital when it is of a higher energy?
Increases
What does a larger n value (principal quantum number) indicate about the energy?
A larger n value indicates a larger orbital which is further away from the nucleus and hence have a higher energy
Within a subshell, what energy do orbitals have?
Degenerate (same energy)
What is the relative energies of the orbitals?
1s (lowest energy), 2s, 2p, 3s, 3p, 4s, 3d (exception), 4p
What is the aim of orbital filling?
Achieve an electronic configuration of the lowest possible energy at the ground state
What are the 3 rules in orbital filling?
- Aufbau principle
- Pauli Exclusion Principle
- Hund’s Rule
What is Aufbau Principle?
Electrons reside in the orbital of lowest possible energy first
(draw the arrow diagram)
What is the Pauli Exclusion Principle?
an orbital can accomodate a maximum of 2 electrons and they must be in opposite spins
What is the Hund’s rule?
Electrons occupy degenerate orbitals singly and with the same spin before pairing occurs
What is the ground state?
The most stable and lowest energy state
What are the exceptions to orbital filling?
Cr and Cu because half-filled or fully-filled d subshell tend to be more stable
What indicates the number of principal quantum shell?
Period number
What is the number of valence electrons equal to?
Group number
How to find group number using spdf notation?
- s-block: sum of valence electrons (sum of number of electrons with the highest principal quantum shell number)
- p-block: sum of valence electrons + 10
- d-block: sum of d + s electrons
Where are the different blocks located?
- s is left two
- d is middle
- p is right
- f is bottom 2 that is separated
What do elements in the same group have?
The same valence shell electronic configuration
How are electrons removed in cation formation?
Electrons are removed from the outermost shell (4s removed before 3d cause 4s is outer)
How are electrons added in anion formation?
Electrons are added to the empty/partially filled outermost orbitals
What is ionisation energy?
Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms or ions (for 1st IE it’s atoms, for 2nd IE it’s ions)
What is the equation for 1st IE?
X(g) → X⁺(g) + e⁻
ΔH = 1st IE of X
What are the factors that affect ionisation energy?
- effective charge (nuclear charge and shielding effect)
- atomic radius
What is the formula for effective nuclear charge?
Zeff = Z - shielding constant
Z: nuclear charge
What affects nuclear charge, Z and what are the implications?
- The larger the number of protons, the greater the nuclear charge
- as nuclear charge increases, the attraction on electrons increases and more energy is required to remove the valence electron
What affects the shielding constant and what are the implications?
- The larger the number of inner principal quantum shell of electrons, the greater the magnitude of shielding constant, the greater the shielding effect
What affects atomic radius?
- as number of filled principal quantum shells increases, atomic radius increases
- as effective nuclear charge increases, atomic radius decreases
How does a larger atomic radius related to ionisation energy?
- A larger atomic radius implies that valence electrons are located further away from the nucleus
- as a result, they experience weaker attractive force from the nucleus and can be removed more easily, hence a lower IE
How does a larger effective nuclear charge affect ionisation energy?
a larger effective nuclear charge implies that the valence electrons are held more strongly to the nucleus and require more energy to be removed
What is the trend of 1st IE across a period?
- 1st IE generally increase across a period
- across a period, nuclear charge increases while there is a negligible increase in shielding effect as electrons are removed from the same shell, thus effective nuclear charge increases
- atomic radius also decreases
- more energy is required to remove the valence electrons that are increasingly more attracted by the positive nucleus
What are the anomalies of the trend of 1st IE across a period?
- 2p electrons to be removed from B has a higher energy than 2s electrons to be removed from Be
- Coulombic repulsion between paired 2p electrons in O makes it easier to remove one of the paired 2p electrons than an unpaired 2p electron from N
What is the trend of 1st IE down a group?
- 1st IE decreases down a group
- down a group, atomic radius increases
- the increase in shielding effect due to increase in number of principal quantum shells is largely cancelled out by the increase in nuclear charge
- less energy is required to remove the valence electrons that become increasingly less attracted by the positive nucleus
How to describe trend of successive ionisation energy and how to use it to predict group number?
- there is an increase in successive IE as the electron is removed from an ion of increasing positive charge
- first two ionisation energies increase gradually as they only involve the removal of outermost 3s electrons only
- sharp increase from 2nd to 3rd IE since it involves the removal of 2p electrons from an inner principal quantum shell
- only two electrons in outermost shell, group II element
Why is there a sharp increase in IE?
- The electron is removed from an inner principal quantum shell which is located nearer to the nucleus
- The electron also experiences lesser shielding effect and greater effective nuclear charge, hence it is more strongly attracted to the nucleus and will require a larger amount of energy to remove
