Unit 2 Material Properties PDF

Unit 4 Material proper.es Presented by Serace.n Haslak 4.1 The structure of the atom All the atoms in a particular element are the same. Different elements have different atoms. For example the atoms in sodium are all the same as one another. They are different from the atoms in po...

Unit 4 Material proper.es Presented by Serace.n Haslak 4.1 The structure of the atom All the atoms in a particular element are the same. Different elements have different atoms. For example the atoms in sodium are all the same as one another. They are different from the atoms in potasium. Atoms are made up of three kinds of particles: protons, neutrons and electrons. The protons and neutrons are grouped closely together in the centre of the atom. They form the nucleus of the atom. The electrons move around the nucleus. 4.1 The structure of the atom The three different particles in an atom have different properties: 1. Protons and neutrons have much more mass than electrons. In fact, electrons have almost no mass at all. 2. Protons have a positive electrical charge. 3. Neutrons have no electrical charge. 4. Electrons have a negative electrical charge. There is a lot of empty space between the parts of the atom. This space really is completely empty – there is nothing in it at all. Ques2ons 1. Which parMcle in an atom has a posiMve electrical charge? 2. Which of the three parMcles that make up an atom has the smalles mass? 3. Which parMcles make up the nucleus of an atom? 4. The size of the negaMve charge of an electron is exactly the same as the size of the posiMve charge of a proton. What is the overall charge of the helium atom shown in the diagram? 4.1 The structure of the atom – How did scien2sts come up with this model of the atom? In the late 1890s a BriMsh scienMst called J.J. Thompson discovered the electron. His model for the atom was that the different parts of the atom were scaVered throughout the structure. 4.1 The structure of the atom – How did scientists come up with this model of the atom? Ernest Rutherford discovered the proton in 1909 and the nucleus in 1911. Rutherfords most famous experiment was the gold foil experiment. In this experiment Rutherford fired fast moving particles smaller than an atom – at very thin goild foil. Most of the particles passed straight through the foil. Only a few of these particles were deflected in various directions. 4.1 The structure of the atom – How did scientists come up with this model of the atom? This led Rutherford to have the idea that gold atoms must be mostly empty space, with their particles packed into a dense nucleus at the centre. James Chadwick worked with Rutherford and Thompson. In 1932, he proved that neutrons exist. Each scientist builds on the discoveries of others. Their experiments and ideas have helped us to understand the structure of the atom. Summary Atoms are made up of protons, neutrons and electrons. The nucleus of an atom is made up of protons and neutrons. Electrons move around the nucleus of an atom. ScienMsts from around the world have helped us understand the structure of the atom. 4.2 More about the structure of the atom – Periodic table 4.2 More about the structure of the atom – Periodic table The atoms of the elements increase in mass as you progress from left to right and downwards in the Periodic Table. For example, an atom of hydrogen has less mass than an atom of sodium. Each element has an atomic number. This tells you how many protons it contains. The atomic number increases by one with every element. Each element has a mass number. This tells you how many protons and neutrons each atom in the element has in total. Protons have a positive charge. Electrons have a negative charge. An atom has no overall charge, because the number of protons is the same as the number of electrons. 4.2 More about the structure of the atom – Periodic table Lets take lithium as an example. Atomic number = 3 Mass number = 7 Number of protons = 3 Number of electrons = 3 Number of neutrons = 4 4.2 More about the structure of the atom – Arranging the electrons The electrons are arranged in electron shells or orbits around the nucleus. This is the electronic structure. The first shell has only room for two electrons. The second and third shells each have room for up to eight electrons. Niels Bohr first had the idea that the electrons move in different shells around the nucleus. 4.2 More about the structure of the atom – Arranging the electrons The arrangement of electrons in an atom is o_en wriVen as numbers. For example, the electron arrangement for an atom of boron can be wriVen as 2,3. This means there are two electrons in the first shell and three in the next shell. The first shell always fills up before electrons fo into the second shell. Ques2ons 1. How many electrons are there in an atom of carbon? 2. How many protons are there in an atom of berylium? You will need to look at the Periodic Table to answer the following questions. 3. How many neutrons are there in an atom of boron? 4. Draw a diagram to show the structure of an atom of magnesium. 5. What is the name of the element that has electrons arranged 2,8,2? 6. Draw a labelled atomic diagramm of the element fluorine. Summary The atomic number tells you how many protons are in the atom. The mass number tells you how many protons + neutrons there are. Electrons are arranged in shells. A shell must be filled before starting on the next one. 4.3 Trends in Group 1 The columns in the Periodic Table are called groups. The first group, also known as the alkali metals, includes the elements lithium, sodium and potassium. These elements have some properMes in common. 4.3 Trends in Group 1 The atomic number increases as you go down the group. The mass number also increases as you go down the group. These increasing numbers show you that the size of the atom is increasing. When you look at the melMng points you can see that they go down as you go down the group. Ques2ons 1. Where in the Periodic Table do you find the metals? 2. What is the trend shown in the boiling points of Group 1 elements? 3. What prediction can you make about the boiling point of rubidium? 4. How many more electrons than lithium does an atom of sodium have? Question - Reactions in Group 1 metals 1. Describe the safety precautions that the the teacher took. 2. Describe what you saw happen when each of the metals reacted with the water. 3. Write the word equation for each reaction. 4. What similarities do you notice about the reactions of these metals? 5. What differences do you notice about the reactions of these metals? 6. List the properties that these elements share. 7. Suggest why the next element in this group, rubidium, is not used in schools. 4.3 Trends in Group 1 – The structure of the Group 1 elements Lithium has an atomic number of 3 and a mass number of 7. This atom contains three protons, 3 electrons and 4 neutrons. The electrons are arranged as 2,1. This arrangement of electrons is known as the electrtonic sVructure. Sodium has an atomic number of 11 and a mass number of 23. This atom contains 11 protons, 11 electrons and 12 neutrons. The electrons are arranged as 2, 8, 1. Potassium has an atomic number of 19 and a mass number of 39. This atom contains 19 protons, 19 electrons and 20 neutrons. The electrons are arranged as 2, 8, 8, 1. 4.3 Trends in Group 1 – The structure of the Group 1 elements Ques2ons 5. What happens to the size of the atoms as you go down this group? 6. What similarity is there in the sVructure of these atoms? (Hint: look at the electron shell arrangemens.) 7. Suggest why this group of metals is called Group I. 8. What are the trends in the structure and behaviour of these elements in Group I. Summary The elements in Group I share some properties. The trend in Group I is that the melting points and the boiling points decrease, as you go down the group. The elements in Group I react more vigorously with water as you go down the group. 4.4 Trends in some other groups The group 7 is sometimes called the halogens. The group includes flourine, chlorine and bromine. 4.4 Trends in some other groups The elements in Group 7 have a number of protperMes in common. The first two elements are gases at room temperature and bromine is a liquid. The most reacMve of these elements is fluorine, the chlorine. Bromine is the least reacMve of the three. Ques2ons 1. Are the halogens metals or non-metals? 2. What is the trend (paVern) in melMng points of this group? 3. What is the trend in boiling points in this group? 4. What is the trend in colour in this group? 5. What would zou predict about the boiling and melMng points of iodine, the next element in this group? 6. Would you expect iodine to be more or less reacMve than bromine? 4.4 Trends in some other groups – The structure of fluorine and chlorine atoms Fluorine has an atomic number of 9 and a mass number of 19. This atom contains 9 protons, 9 electrons and 10 neutrons. The electrons are arranged as 2,7. Chlorine has an atomic number of 17 and a mass number of 35. This atom contains 17 protons, 17 electrons and 18 neutrons. The electrons are arranged as 2, 8, 7. Questions 7. What happens to the size of the atoms as you go down this group? 8. What similarity is there in the structure of these atoms? (Hint: look at the electron shell arrangements.) 9. Suggest why this group is called Group 7. 4.4 Trends in some other groups – Group 8 – the noble gases Group 8 includes the elements helium, neon and argon. They are all gases. They are inert (unreacMve) and do not form compounds. They are called noble gases. 4.4 Trends in some other groups – Group 8 – the noble gases Helium has an atomic number of 2 and a mass number of 4. This atom contains 2 protons, 2 electrons and 2 neutrons. The electrons are arranged with 2 in the first shell. The shell is full. Neon has an atomic number of 10 and a mass number of 20. This atom contains 10 protons, 10 electrons and 10 neutrons. The electrons are arranged with 2 in the first shell and 8 in the second shell. The outer shell is full. Argon has an atomic number of 18 and a mass number of 40. This atom contains 18 protons, 18 electrons and 22 neutrons. The elecVrons are arranged with 2 in the first shell and 8 in the second and third shells. The outer shell is full. 4.4 Trends in some other groups – Group 8 – the noble gases Questions 10. What trend in melting points can be seen in Group 8? 11. What happens to the size of the atoms as you go down Group 8? 12. What similarity is there in the structure of these atoms? 13. Suggest why this group is called Group 8. Summary The elements in each group share some properMes. The elements in Group 7 react less vigorously as you go down the group. The elements in Group 8 have all their electron shells full and do not react to form compounds. Homework 1. The table shows some informaMon about four elements. These elements are from the same group in the Periodic Table. They are given in the same order as in the Periodic Table. Homework There is a trend in the melting and boiling points of these elements. Use the trend to predict the following: a. The melting point of sodium b. The boiling point of potassium c. The elements all react with water to produce a gas. Name the gas. d. Use the information about the reaction with water to predict the reaction between sodium and water. e. The following are the mass numbers of the four elements in the table above. They represent the relative size of the atoms. 23; 7; 39; 85. Match the numbers with the elements. Homework f. Lithium has 2 electron shells. The electronic structure is 2,1. This can be seen in the diagram below. Sodium has the electronic structure 2, 8, 1. Draw a similar diagram to show the electronic structure of sodium. Homework 2. Many scienMsts contributed to the model of the atom that is shown in the diagram below. a. Copy the diagram and label it using the following words: Electron: nucleus; proton; neutron. Homework Name the parMcle that: b. Has a posiMve charge c. Has no charge d. Has the least mass e. Is present in the same numbers as the protons in an atom. Homework 3. a. Neon is noble gas. It has the electronic structure 2,8. Which of the diagrams, A, B, C or D, shows the electronic structure of neon? Homework b. How many protons does the atom of neon have? Neon is in Group 8 of the Periodic Table. Other gases in this group are helium and argon. c. The elements in Group 8 are sometimes called the noble or inert gases. Helium has only one shell of electrons, neon has two and argon has three. What do the shells of this group have in common? d. How are elements in Group 8 different from all other elements in the Periodic Table?