Unit 1.2

• Some isotopes are unstable and split up to form smaller atoms. The nucleus divides and sometimes protons, neutrons and electrons fly out. This is called radioactive decay.
• Radioactive isotopes have unstable nuclei and give off three types of radiation: alpha, beta and gamma
• Alpha particles consist of 2 protons and 2 neutrons (a helium nuclei). They are the least penetrating radiation however they are the most ionising.
• Beta particles are streams of high energy electrons and are more penetrating than alpha particles however beta is less ionising.
• Gamma rays are high energy electromagnetic waves and are the most penetrating but least ionising of the radiation types.
• Ionisation is the process of removing electrons from atoms making them positively charges. Alpha particles are large and slow moving, enabling them to knock out many electrons.
• Ionisation involves the transfer of energy from the radiation passing through the matter to the matter itself.
• Alpha particles are deflected to a negatively charged plate by a magnetic field. This demonstrates that they are positively charged.
• Beta particles are deflected by a magnetic field towards a positively charged plate, demonstrating that beta particles are negatively charged.
• Gamma rays are unaffected hy a magnetic field which shows that they are uncharged.
• When an element emits and alpha particles, the elements mass number decreases by 4 and its atomic number decreases by 2
• When an element emits a beta particles, its mass number remains unchanged but its atomic number increases by 1
• Electron capture is the inverse of beta decay. An electron is captured by a proton in the nucleus, forming a neutron amd emitting an electron neutrino. The atomic number of the element decreases by 1.
• Positron emission or beta positive decay is when a proton is converted into a neutron while releasing a positron. The atomic number of an element decreases by 1.
• The time taken for radioactive isotopes to decay to half the number of radioactive atoms is known as the half life.
• We all recieve some radiation from the normal background radiation that occurs everywhere
• Ionising radiation may damage the DNA of a cell. This could cause changes in the way the cell functions. This can lead to mutations and the formation of cancerous cells.
• Colbalt-60 is used in radiotherapy for the treatment of cancer. The high energy of gamma radiation is used to kill cancer cells
• carbon-14 is used to calculate the age of plants and animal remains. All living things absorb carbon (includibg carbon-14). The rate of decay decreases over the years and the activity that remains can be used to calculate the age of organisms.
• Beta emitters can measure the thickness of metal strips or foil.
• atomic orbitals are regions of space around the nucleus where there is an increased probability of an finding an electron there.
• Along with charge, electrons have a property called spin. In order for two electrons to exist in the same orbital, they must have opposite spins. This reduces the effect of repulsion.
• There are 4 different subshells which hold different numbers of electrons. An S subshell holds 2 electrons, a P subshell holds 6 electrons, a D subshell holds 10 and an F subshell holds 14.
• Electrons fill atomic orbitals in order of increasing energy. 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p...
• A maximum of two electrons can occupy any orbital each with opposite spin (Pauli exclusion principle)
• The orbitals will first fill with one electron each with parallel spins, before a second electron is added with the paired spin.
• The 4s subshell is filled before the 3d.
• there are 2 exceptions to the electronic structure: Copper and chromium. copper (29) is [Ar] 3d10 4s1. Chromium (24) is [Ar] 3d5 4s1
• The process of removing electrons from an atom is called ionisaton. The energy needed to remove each successive electron from an atom is called the first, second, third etc ionisation energy.
• X(g) -> X(+)(g) + e(-) is the equation for the first ionisation energy
• electrons are held in their shells by their attraction to the positive nucleus, therefore the greater the attraction, the greater the ionisation energy.
• The greater the nuclear charge, the greater the attractive force on the outer electron and the greater the ionisation energy.
• the force of attraction between the nucleus and the outer electron decreases as the distance increases. The further an electron is from the nucleus, the lower the ionisation energy.
• All electrons repel each other as they are all slightly negative. Electrons in the inner shells repel the outer electrons and reduce the affect of the positive nuclear charge. The more inner shells there are, the smaller the attractive force on the outer electron.
• There is a general increase in ionisation energy across a period.
• Beryllium has a higher ionisation energy than boron because the 2p orbital is further away from the nucleus and is shielded by the 2s orbital.
• Nitrogen has a higher ionisation energy than oxygen because the electron-electron repulsion between 2 paired electrons in one p orbital in oxygen makes the electron easier to remove.
• evidence for shells and subshells comes from the successive ionisation energies needed to remove all the electrons from an atom. An element has as many ionisation energies as it has electrons
• Successive ionisation energies always increase because there is a greater effective nuclear charge as the same number of protons are holding fewer electrons, as each electron is removed there is less electron-electron repulsion and each shell will be drawn slightly closer to the nucleus, and as the distance between the electron and nucleus decreases the nuclear attraction increases.
• Light is a form of electromagnetic radiation (energy travelling through waves).