1. a Draw a labelled diagram of an atom that has 9 protons and electrons and 9 neutrons.

Transcription

1 Topic review Using scientific language Design and construct a crossword using the following words: atom; proton; molecule; ion; lattice; shell; element; compound; bond; conductor; insulator; electrolysis; fission. Exchange your crossword with another student and complete it. Check your knowledge 1. a Draw a labelled diagram of an atom that has 9 protons and electrons and 9 neutrons. b What type of atom is this? c Which other element would you expect to behave most like this element?

2 2. a Draw and label a molecule of water and a molecule of oxygen. b Both are molecules but only one is an element. Explain this statement. 3. An atom of sodium has 11 protons and 11 electrons. How does an ion of sodium differ from this? 4. What is an electron shell? What is the valence shell?

3 5. What are the major similarities and differences between protons, neutrons and electrons? 6. Why can metals be bent and shaped when ionic substances cannot? 7. Why does a saucepan of hot water with a lid on cool more slowly than one without a lid? 8. An atomic explosion can begin by splitting atoms of uranium. If an uncontrolled chain reaction occurs there is a massive release of energy. Draw a labelled diagram to show how a chain reaction takes place. You will need to show the nuclei of the atoms but you need not show electrons.

4 Apply your skills 1. Brownian motion is given as evidence to support the existence of atoms. Explain why this supports the idea that atoms exist. 2. Look at the image below then answer the questions that follow. (Refer to the modern periodic table.) a What type of atom is it? b Is it a metal or non-metal? c Which group is it in? Name one other element in this group.

5 d Which row of the periodic table is it in? Give the name of the atom that has one more proton than the atom in the diagram. 3. Which element has 4 valence electrons and 3 electron shells? 4. Dry ice is solid carbon dioxide. At room temperature dry ice changes directly from a solid to a gas. Use your understanding of molecules to explain what has happened. In your answer suggest why there is no liquid phase.

6 5. Why does salty water conduct electricity when pure water does not? 6. Explain (using diagrams) what type of bond you would have between the two atoms of nitrogen making up a nitrogen molecule.

7 7. Potassium and chlorine will react to form an ionic lattice. Look first at the periodic table and then draw what you think a small part of this lattice would look like. Do you think it is correct to call this a molecule? Explain. 8. Why do metals tend to form positive ions and non-metals form negative ions?

8 Challenge yourself The image below shows a circuit through which an electric current is flowing. The current is the movement of charged particles through the circuit. Draw and label diagrams to show what is happening at points A and B of the circuit. You should clearly show which particles are moving and which are not.

9 Answers Check your knowledge 1. a 2. a b fluorine c chlorine b Water contains hydrogen and oxygen; therefore it is a compound. An oxygen molecule contains only oxygen atoms; therefore it is an element. 3. Na + has 11 protons and 10 electrons. 4. Electron shells are the area around the nucleus in which the electrons orbit. The valence shell is the outer shell containing the valence electrons. 5. Differences: protons are positively charged, electrons are negatively charged and neutrons are uncharged. Similarities: the mass of the proton and the neutron are similar and the size of the charge on the proton and the electron is the same. 6. The metallic bonding of atoms in a metallic lattice is sufficiently strong that the atoms can be forced to move without breaking up the lattice; electrons can move relatively freely within the lattice allowing bending of the lattice without shattering. In ionic substances the positive and negative ions are strongly attracted to each other and held in an ionic lattice forming rigid, brittle crystal structures. 7. The water molecules 'escaping' from the saucepan without a lid take the energy with them.

10 8. Apply your skills 1. Brownian motion observed in visible smoke particles is evidence for the existence of atoms as it is believed that the movement is caused by rapidly moving atoms and molecules crashing into the smoke particles. 2. a A sulfur atom (16 electrons) b non-metal c Group VI; oxygen, selenium, tellurium or polonium d third; chlorine 3. Total 14 electrons silicon. 4. Changing directly from a solid to a gas is sublimation. (Iodine also sublimes.) The atoms are moving so fast when they break their bonds in the solid that they form a gas without passing through the liquid phase. 5. Salty water contains ions which can move to conduct an electric current. Pure water does not contain ions. 6.

11 7. 8. Metals have valence electrons which are easy to remove, e.g. Na has 1 valence electron in its outer shell which is easy to remove to create a stable outer shell. Challenge yourself