Chemistry IB HL: Atomic Structure

Mass number

The number of protons plus the number of neutrons

Atomic number

The number of protons in the nucleus

Isotopes

Atoms of the same element with the same number of protons (atomic number) but a different number of neutrons (mass number)

Properties of isotopes

Same chemical properties, different physical properties (e.g. boiling/melting point)

Relative atomic mass (Ar)

Ratio of the average mass of the atom to the unified atomic mass unit

Formula for relative atomic mass

(abundance x mass) + (abundance x mass) ... for however many isotopes there are

Mass spectrometer

An apparatus that can give information about isotopic composition of different elements and the structure of molecules.

A larger deflection occurs when?

The atom has a higher charge and a smaller mass

Detection

Ions with particular mass/charge ratio are recorded on a detector. The mass and relative amounts of ions present are measured

Line Spectrum

Discrete narrow bands of colour. Only shows discrete energy levels and specific colours/wavelengths/frequencies

Continuous Spectrum

Full spectrum of light, each colour merging into the next (no gaps). Shows all energy levels and colours/wavelengths/frequencies

Ionisation energy

The minimum energy required to remove an electron from the ground state of a gaseous atom/ion/molecule

When do lines converge in the line spectrum?

At higher energies (energy levels inside the atoms are closer together)

Balmer series

Visible light. Energy levels 7-2

Radioisotope

An unstable isotope of an element, which undergoes radioactive decay

Alpha particle

Emitted by nucleus when there are too many protons in it; it is not stable. Composed of two protons and two neutrons.

Beta particle

Emitted by nucleus when there are too many neutrons. Composed of electrons

Carbon-14 dating

Living creatures have particular isotopes of Carbon, which remains constant throughout life. When dead, these isotopes start to decay into nitrogen. This decay (half-life) can be measured and thus the dead creature can be dated back to when it lived.

Electromagnetic spectrum

arrangement of electromagnetic radiation. including radio waves, visible light , gamma rays, X rays, ultraviolet waves, infrared waves, and microwaves--according to their wavelengths

Excited state

The unstable energy of an electron, which is disposed of when the electron falls down to the ground state

Ground state

The stable energy of an electron

Valence electrons

Outer shell electrons

Ion

When electron number differ from proton number, the atom carries a charge.

Cation

Positive Ion

Anion

Negative Ion

Mass spectrum

A graph with % abundance plotted against mass/charge, gained as a result from the mass spectrometer.

Electron arrangement

Organization of electrons in an atom by increasing energy shells.

Frequency

the number of complete wavelengths that pass a point in a given time

Wavelength

the length from one crest to another

First ionization energy

The minimum energy required to remove one mole of electrons from one mole of gaseous atoms in their ground state.

Electron configuration

the arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms

sub-level

s, p, d, f; denotes shape of orbital

How many electrons can there be occupied in a s orbital?

2

State the maximum amount of electrons that can fill up a p orbital.

6

State the maximum amount of electrons that can up a d orbital.

10

State the maximum amount of electrons that can up a f orbital.

14

What is the Heisenberg uncertainty principle?

State the principle that states the following: it is impossible to determine accurately both momentum and position of a particle simultaneously. The more we know about the position, the less we know about the momentum, and vice versa. We can calculate the PROBABILITY of finding an electron in a given region of space within the atom.

Atomic orbitals

The regions around the nucleus within which the electrons have the highest probability of being found

What is the Pauli exclusion principle?

Paired electron will have opposite spin, as this reduces the mutual repulsion between the paired electrons.

What does the Aufbau principle state?

The principle that states that electrons fill the lowest orbitals first.

What does Hund's rule state?

electrons fill degenerate orbitals as to give the maximum number of electrons with parallel spins.

Outline the prperty of electrons that is Electron spin?

An intrinsic property of electrons that causes each electron to behave as if it were spinning about an axis. The spinning charge generates a magnetic field whose direction depends on the direction of spin.

Proton: type of particle, charge, location & mass

Sub-atomic particle, charge of 1+, located in the nucleus, weighs approximately 1amu

Neutron: type of particle, charge, location & mass

Sub-atomic particle, charge of 0, located in the nucleus, weighs approximately 1amu

Electron: type of particle, charge, location & mass

Sub-atomic particle, charge of 1-, located outside the nucleus in different energy levels, weighs 0amu or 1/1836

How the mass spectrometer works

Particles are vaporized, released into machine, are bombarded by electrons until they become positively charged, their breakdown is accelerated by an electrical field, certain masses land on the deflector, based on what goes through and what doesn't, the machine categorizes the particles

When electrons absorb energy they

Go to a higher energy level, when they return they release a photon.

S-block

Groups 1-2

D-block

Groups 3-12

P-block

Groups 13-18

Orbital

A region of space in which an electron may be found

Orbital diagram

A diagrammatic representation of electron configuration showing electrons as arrows in boxes

Quantum theory

Energy can be absorbed or emitted in 'packets' or quanta

Stability

The amount of energy possessed by a particle. The greater the stability, the lower the energy of that particle and the lower the chance of it reacting to form another species

S Orbital shape

P Orbital shape

What's a photon?

a tiny particle or packet of light energy

Schrödinger's equation

mathematical equation that describes electron shells more as diffused clouds of probability that relate to a wave function than a sharply defined orbital.

What are two exceptions to the Aufbau principle?

The electronic structures of chromium and copper do not follow the pattern - they are anomalies.

Chromium - 1s2, 2s2, 2p6, 3s2, 3p6, 3d5, 4s1

Copper - 1s2, 2s2, 2p6, 3s2. 3p6, 3d10, 4s1

Isoelectronic Structure

Ions that contain the same number of electrons, therefore have the same electron configuration

de Broglie's equation

An equation that describes the wavelength of a moving particle; it predicts that all matter exhibits wavelike motions. Shows that macroscopic particles have too short a wavelength for their wave properties to be observed.

The value of the first ionization energy depends upon two main factors:

1. The size of the nuclear charge

2. The energy of the electron that has been removed (this depends upon its distance from the nucleus)

Limit of Convergence

Lines converge at the higher energies in the emission spectrum for hydrogen creating a continuum.

Past this continuum electrons are removed from the atom, which is ionization. Ionization of an atom occurs when an electron gains energy to move from n=1 to n=∞

Why is there a general increase in ionisation energies across a period?

The positive nuclear charge increases from left to right. The electrons are added to the same shell and electrons in the same shell do not shield each other very vell from the positive charge of the nucleus. Therefore the outer electrostatic force on the electrons increases

Exception to Period Trends

The first ionisation of Al is less than that of Mg, despite the increase in the nuclear charge. The reason for this is that the outer electron removed from Al is in a higher sub-level: the electron removed from Al is a 3p electron, whereas that removed from Mg is a 3s. If the 3p electron removed from S is a paired electron, whereas the 3p electron removed from P is an unpaired electron. When the electrons are paired the extra mutual repulsion results in less energy being required to remove an electron, hence a reduction in the ionisation energy.

Successive Ionization energy

ionization energy increases as you take away electrons

Trends down a Group

Ionization energy decreases going down a Group.

Energy Level Diagram for Hydrogen

% of heavier Isotop

(Ar- Mass of lighter I)/(Difference in Mass No)

How do we observe the electromagnetic spectrum?

A discharge tube allows our eyes to differentiate the colours and their separate wavelengths.

How do the series of lines occur?

When the electrons fall to different levels

Why does Boron have a lower first ionisation energy than Beryllium?

Boron has an electron in the 2p sublevel. Wheras the outer electron is in a 2s orbital in Be. The 2p sublevel is higher in energy than the 2s orbital and therefore less energy is required to remove the electron in the higher energy level.