surrounded by negatively charged electrons. The radius of a nucleus is less than 1/10,000 of the radius of an atom. Most of the mass of an atom is concentrated in the nucleus. The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) of by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level). Describe the composition of an atom and draw a fully labelled diagram of an atom showing protons and neutrons in the nucleus with electrons outside the nucleus. Give the charges of all particles within the atom. Calculate the size of an atom given the size of the nucleus and the scale of the nucleus compared to the atom. Describe how the concentration of mass of an atom is not uniform but concentrated on the nucleus of the atom. Describe how electrons are arranged within an atom. Describe and explain how electrons can be moved further away from the nucleus of the atom and how they lose energy to move closer to the nucleus. Explain how the wavelength of the electromagnetic wave emitted by an electron changes in relation to how far the electron has moved towards the nucleus. Research how absorption and emission spectra are formed.
number of protons and neutrons in the atom. Rearrange the equation to find number of protons or number of neutrons and the mass number. Explain how isotopes of elements, all have the same number of protons but have a different number of neutrons. Define isotope. Describe an atom in terms of number of protons, neutrons and electrons when given the following representation . 6.4.1.3 Scientific models of the atom and how these models have changed. New experimental evidence may lead to a scientific model being changed or replaced. Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided. The discovery of the electron led to the ‘plum-pudding model’ of the atom. The ‘plum-pudding model’ 0.6 Why has the model of the atom changed since ancient Greek times? Describe and explain why scientific models are replaced. Describe why ancient Greeks thought that the atom not be divided. Draw a diagram to illustrate the ‘plum-pudding model’ of the atom. Model the alpha scattering experiment by flicking a 1p coin through stack of 2p coins. The 1p coin represents the alpha particle and the stack of 2p coins the gold foil. How must the stacks be arranged in order that 90% of the coins go straight through without Video clip YouTube: Video clip YouTube: Past Exam Questions – Exampro ref: 1. QCJ98H3.13 2. Q13W.Y2H.08
suggested that the atom was a ball of positive charge with negative electrons embedded in it. The results from thealpha scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. The alpha scattering experiment led to the model’ being replaced by the nuclear model. Neils Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name ‘proton’ was given to these particles. Explain why the ‘plum-pudding model’ was ‘better’ than the Greek model of the indivisible atom. Describe the alpha scattering experiment What was so amazing about the alpha scattering experiment? Details of these experiments are not required. Explain how the evidence from the scattering experiment led to a change in the atomic model of the atom. Describe the difference between the ‘plum-pudding model’ of the atom and the nuclear model of the atom. Produce a timeline to show how our ideas about atoms have changed since ancient Greek times. Find out about the origins of the words protons, neutrons and electrons. scattering? What conclusion can be drawn about the arrangement of atomic nuclei in a material and the amount of free space between nuclei? 3. Q12WY2H05 4. Q09W.2H.07 5. QB04.F.16
Determine the half-life of the cubes (the number of throws needed to get the number of cubes to reduce by half). This experiment can also be carried out using coins. Is it possible to predict which cubes or coins will land on a certain side? 6.4.2.4 How to handle radioactive sources safely to avoid contamination. Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard. 0.7 Describe how radioactive contamination can occur. If radiation is dangerous, why is it used in schools? How would a person become contaminated by radiation? Explain how the procedure followed by people dealing with radioactive sources reduces the risk of contamination. If a person gets contaminated by radiation how are they decontaminated? Compare precautions taken by a teacher handling radioactive sources with those used by, say, in a nuclear power station.