IB Chemistry Topic 2/12

What did John Dalton propose about atoms?

All matter is composed of tiny, indivisible particles called atoms

Atoms cannot be created or destroyed

Atoms of the same element are alike in every way

Atoms of different elements and different

Atoms can combine together in small numbers to form molecules

What was JJ Thomsons model of the atom

Plum pudding model, negatively charged electrons scattered in a positively charged sponge-like substance.

What did Rutherford discover during his gold foil experiment

The atom is mainly empty space, there is a dense, positively charged centre called the Nucleus.

What was Bohrs model of the hydrogen atom

a small “solar system” electrons move in orbit of a nucleus made up of one proton. Electrostatic forces prevent the electron from leaving. He also discovered neutrons are required for stability in atoms with more than 1 proton.

What is the equation for relative atomic mass

Equation for relative atomic mass: (mass of isotope 1 x % abundance of isotope 1) + (mass of isotope 2 x % abundance of isotope 2) + ... divided by total abundance and then multiplied by 100

What is used to measure the mass of individual atoms

mass spectrometer

How can the relative atomic mass be deduced from a mass spectra

The horizontal axis shows the mass/charge ratio of different ions on the carbon 12 scale, which is equivalent to the mass

The vertical axis shows percentage abundance.

How are wavelength and frequency related

Speed of light = frequency x wavelength

What happens when EM radiation is passed through a collection of atoms

Some of the radiation is absorbed and used to excite atoms from a lower energy level to a higher energy level. This produces an absorption spectra

What happens when an atom absorbs energy?

An electron is promoted to the excited state, however this is unstable and the electron falls down to ground level. The energy produced when the electron falls is EM radiation. One photon is released per electron transition. The energy of a photon is equal to the energy of the electron.

What happens when electrons fall to certain energy levels in a hydrogen atom

Hydrogen produces visible light when the electron falls to the second energy level (n = 2)(Balmer series). The transitions to the first energy level (n = 1) correspond to a higher energy change and are in the ultraviolet region of the spectrum (Lyman series) . Infrared radiation is produced when an electron falls to the third or higher energy levels (Paschen series)

What is the first energy level made up of

One 1s orbital, which can hold 2 electrons.

Holds 2 electrons in total

What is the second energy level made up of

One 2s orbital, which can hold 2 electrons

Three 2p orbitals, which can hold 2 electrons each. This makes the 2p sublevel.

Holds 8 electrons in total

What is the third energy level made up of

One 3s orbital, which can hold 2 electrons

Three 3p orbitals, which can hold 2 electrons each. This makes the 3p sublevel.

Five 3d orbitals which can hold 2 electrons each. This makes the 3d sublevel.

Holds 18 electrons in total

What is the shape of the 3 types of orbitals

s orbitals are shaped as a sphere

p orbitals are dumbell shaped

d orbitals create a four leaf clover shape

What is the Aufbau principle

The Aufbau principle states that electrons fill the lowest energy levels first before moving to higher energy levels in an atom.

What is Hund’s rule

Hund's Rule states that electrons will occupy orbitals of the same energy level singly before pairing up. This minimises mutual repulsion.

What is the first ionisation energy

The minimum energy required to remove one electron from a neutral atom in its gaseous state. It measures the atom's ability to hold onto its electrons.

Why do successive ionisation energies change

It increases as the first ionisation removes an electron from a singly charged ion, and the second from a doubly charged ion. This becomes more an more different due to increasing electrostatic attraction between the nucleus and electrons

A graph of successive ionisation energies will jump when electrons are removed from an energy level closer to the nucleus.

How does ionisation energy change across a period

Ionisation energy across a period increases. As you move from left to right, the number of protons in the nucleus increases, resulting in a stronger attractive force. This requires more energy to remove an electron, hence the increase in ionisation energy.

How does ionisation energy change down a group

Ionisation energy decreases down a group in the periodic table due to an increasing atomic radius making it easier to remove an electron from the outermost shell, requiring less energy. The inner electrons act as a barrier, reducing the attractive force between the nucleus and outermost electrons.