2.1 The Atom
2.1.1 State the position of protons, neutrons, and electrons in the atom.
Protons and neutrons make up the nucleus of an atom, while the electrons orbit the nucleus in different electron shells in a region called the electron cloud.
2.1.2 State the relative masses and relative charges of protons, neutrons, and electrons. Subatomic particle | Mass (kg) | Relative Mass | Charge (C) | Relative Charge | Proton | 1.6726×10-27 | 1 | +1.6022×10-19 | +1 | Neutron | 1.6749×10-27 | 1 | 0 | 0 | Electron | 9.1094×10-31 | 5×10-4 | -1.6022×10-19 | -1 |
Use the relative mass instead of the actual mass in order to make it easier to talk about. Electron’s mass is negligible compared to the mass of a proton or a neutron.
2.1.3 Define the terms mass number (A), atomic number (Z), and isotopes of an element.
Mass number (A) – The sum of the number of protons and neutrons in the nucleus. It must be an integer.
Atomic number (Z) – The number of protons in the nucleus. This is equal to the number of electrons in the atom.
Isotopes – Atoms of the same element with the same number of protons, but different number of neutrons.
2.1.4 Deduce the symbol for an isotope given its mass number and atomic number.
Z
Z
An isotope will have a different number of neutrons, we can figure out the number of neutrons by subtracting the atomic number from the mass number. Isotopes will have a different A, but the same Z, in the nuclide notation. (AX)
2.1.5 Calculate the number of protons, neutrons and electrons in atoms and ions from mass number, atomic number and charge.
From the atomic number we know how many protons the element has. Since no two elements can have the number of protons, we know for certain what element it is. It also tells us how many electrons there are. The atomic number tells us how many protons and neutron, so we subtract the atomic number from the mass number to find the number of neutrons. The superscripted number to the right of the element in the nuclide notation is the charge of the element. This tells us how many electrons were lost or gained. A positive number means it lost that many electrons, and a negative number means that it gained that many electrons.
2.1.6 Compare the properties of the isotopes of elements.
The chemical properties of isotopes will be the same as they are dependent of the number of electrons, however physical properties are dependent on the number of particles in the nucleus. This means that an isotope may have a different melting point, boiling point, rate of diffusion and/or nuclear properties.
2.1.7 Discuss the uses of radioisotopes.
Many isotopes are radioactive, some are dangerous, and some are useful. For example radiocarbon dating, Carbon-14 and Carbon-12 exist in a set ratio in a living organism, but when it dies Carbon-14 begins to decay, Carbon 12 does not. The percentage is used to estimate the age of dead organism. Cobalt-60 is used in radiotherapy, levelling devices and to sterilize foods and spices. Iodine-131 and 125 are used as medical tracers in the treatment for thyroid disorders and prostate cancer/ brain tumours respectively. They are absorbed in the thyroid gland, and the radiation kills some of it.
On the other hand there is radiation poisoning, which refers to acute problems caused by a large dosage of radiation from radioisotopes in a short period.
2.2 The Mass Spectrometer
2.2.1 Describe and explain the operation of a mass spectrometer.
Mass spectrometers are used for analysis of substances.
Stages in the mass spectrometer 1. Vaporization- The sample is heated to a gas and passed into an evacuated tube. This breaks the sample into its components. 2. Ionization- The atoms/molecules are hit with a stream of high energy electrons and one or more electrons are knocked off each atom/molecule. This creates an ion with a +1 (sometimes +2) charge. 3. Acceleration- The positively charged ions are