vasugoel/K-12BERT
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0 | All the objects that we see in the world around us, are made of matter |
1 | Matter makes up the air we breathe, the ground we walk on, the food we eat and the animals and plants that live around us |
2 | Even our own human bodies are made of matter!Different objects can be made of different types of materials (the matter from which objects are made) |
3 | For example, a cupboard (an object) is made of wood, nails, hinges and knobs (the materials) |
4 | The properties of the materials will affect the properties of the object |
5 | In the example of the cupboard, the strength of the wood and metals make the cupboard strong and durable |
6 | Materials that are malleable can be easily formed into different shapes (eg clay, dough) |
7 | Ductile materials are able to be formed into long wires (eg copper) |
8 | The boiling and melting points of substances tells us the temperature at which the substance will boil or melt |
9 | This helps us to classify substances as solids, liquids or gases at a specific temperature |
10 | The diagram below shows one way in which matter can be classified (grouped) according to its different properties |
11 | As you read further in this chapter, you will see that there are also other ways of classifying materials, for example according to whether or not they are good electrical conductors. |
12 | In this chapter we will explore the states of matter and then look at the kinetic molecular theory |
13 | We will also examine how the kinetic theory of matter helps explain boiling and melting points as well as other properties of matter |
14 | Diffusion can be seen as a spreading out of particles resulting in an even distribution of the particles |
15 | You can see diffusion when you place a drop of food colouring in water |
16 | If matter were not made of particles that are constantly moving then we would only see a clump of colour when we put the food colouring in water, as there would be nothing that could move about and mix in with the water |
17 | In 1828 Robert Brown observed that pollen grains suspended in water moved about in a rapid, irregular motion |
18 | Brownian motion can also be seen as the random to and fro movement of particles |
19 | Matter exists in one of three states, namely solid, liquid and gas |
20 | A liquid takes on the shape of the container that it is in |
21 | Matter can change between these states by either adding heat or removing heat |
22 | As we heat an object (eg water) it goes from a solid to a liquid to a gas |
23 | Evaporation from a liquid's surface can happen at a wide range of temperatures |
24 | If more energy is added then bubbles of gas appear inside the liquid and this is known as boiling |
25 | Sublimation is the process of going from a solid to a gas |
26 | Deposition is the process of going from a gas to a solid |
27 | If we know the melting and boiling point of a substance then we can say what state (solid, liquid or gas) it will be in at any temperature |
28 | A heating curve of a substance gives the changes in temperature as we move from a solid to a liquid to a gas |
29 | A cooling curve gives the changes in temperature as we move from gas to liquid to solid |
30 | An important observation is that as a substance melts or boils, the temperature remains constant until the substance has changed state |
31 | This is because all the heat energy goes into breaking or forming the bonds between the molecules |
32 | The following diagrams give examples of what heating and cooling curves look like: |
33 | We have now looked at many examples of the types of matter and materials that exist around us and we have investigated some of the ways that materials are classified |
34 | In order to understand this, we need to take a closer look at the building blocks of matter — the atom |
35 | Atoms are the basis of all the structures and organisms in the universe |
36 | The planets, sun, grass, trees, air we breathe and people are all made up of different combinations of atoms.Video: VPrkk |
37 | The periodic table of the elements is a method of showing the chemical elements in a table with the elements arranged in order of increasing atomic number |
38 | Most of the work that was done to arrive at the periodic table that we know can be attributed to a Russian chemist named Dmitri Mendeleev |
39 | Mendeleev designed the table in 1869 in such a way that recurring (periodic) trends or patterns in the properties of the elements could be shown |
40 | Using the trends he observed, he left gaps for those elements that he thought were “missing” |
41 | He also predicted the properties that he thought the missing elements would have when they were discovered |
42 | Many of these elements were indeed discovered and Mendeleev's predictions were proved to be correct |
43 | To show the recurring properties that he had observed, Mendeleev began new rows in his table so that elements with similar properties were in the same vertical columns, called groups |
44 | The full periodic table is reproduced at the front of this book |
45 | These are the energies needed to remove the second, third, or fourth electron respectively |
46 | If you look at a periodic table, you will see the groups numbered at the top of each column |
47 | The groups are numbered from left to right starting with 1 and ending with 18 |
48 | This is the convention that we will use in this book |
49 | On some periodic tables you may see that the groups are numbered from left to right as follows: 1, 2, then an open space which contains the transition elements, followed by groups 3 to 8 |
50 | A period is a horizontal row in the periodic table of the elements |
51 | The periods are labelled from top to bottom, starting with 1 and ending with 7 |
52 | For each element on the periodic table we can give its period number and its group number |
53 | We can also determine the electronic structure of an element from its position on the periodic table |
54 | In Chapter 4 you worked out the electronic configuration of various elements |
55 | Using the periodic table we can easily give the electronic configurations of any element |
56 | For example, phosphorus () is in the third period and group 15 |
57 | Looking at the figure above, we see that the p-orbital is being filled |
58 | Similar trends are observed in the other periods of the periodic table |
59 | The chlorides are compounds with chlorine and the oxides are compounds with oxygen |
60 | no oxides, but fluorine does combine with oxygen in compounds called oxygen fluorides |
61 | Draw a line graph to show the relationship between atomic number (on the x-axis) and ionisation energy (y-axis) |
62 | A chemical bond is formed when atoms are held together by attractive forces |
63 | This attraction occurs when electrons are shared between atoms, or when electrons are exchanged between the atoms that are involved in the bond |
64 | The sharing or exchange of electrons takes place so that the outer energy levels of the atoms involved are filled, making the atoms are more stable |
65 | If an electron is shared, it means that it will spend its time moving in the electron orbitals around both atoms |
66 | If an electron is exchanged it means that it is transferred from one atom to another |
67 | In other words one atom gains an electron while the other loses an electron.Chemical bond A chemical bond is the physical process that causes atoms and molecules to be attracted to each other and held together in more stable chemical compounds |
68 | The type of bond that is formed depends on the elements that are involved |
69 | In this chapter, we will be looking at three types of chemical bonding: covalent, ionic and metallic bonding.You need to remember that it is the valence electrons (those in the outermost level) that are involved in bonding and that atoms will try to fill their outer energy levels so that they are more stable |
70 | The noble gases have completely full outer energy levels, so are very stable and do not react easily with other atoms. |
71 | A medium is the substance or material through which a pulse moves |
72 | The medium does not create the pulse and the medium is not the pulse |
73 | Therefore the medium does not travel with the pulse as the pulse moves through it.In each medium, the particles that make up the medium are moved temporarily from their rest position |
74 | In order for a pulse to travel, the different parts of the medium must be able to interact with each other.Medium A medium is the substance or material in which a pulse will move |
75 | The most obvious examples are waves in water, on a dam, in the ocean, or in a bucket |
76 | All waves have the same properties.Waves do not only occur in water, they occur in any kind of medium |
77 | Earthquakes release enough energy to create waves that are powerful enough to travel through the rock of the Earth |
78 | When your friend speaks to you sound waves are produced that travel through the air to your ears |
79 | A wave is simply the disturbance of a medium by moving energy but how is it different from a pulse? |
80 | Longitudinal waves A longitudinal wave is a wave where the particles in the medium move parallel to the direction of propagation of the wave |
81 | When we studied transverse waves we looked at two different motions: the motion of the particles of the medium and the motion of the wave itself |
82 | We will do the same for longitudinal waves.The question is how do we construct such a wave?A longitudinal wave is seen best in a slinky spring |
83 | Do the following investigation to find out more about longitudinal waves.From the investigation you will have noticed that the disturbance moves parallel to the direction in which the spring was pulled |
84 | The ribbon in the investigation represents one particle in the medium |
85 | The particles in the medium move in the same direction as the wave.Video: VPdkfAs in the case of transverse waves the following properties can be defined for longitudinal waves:wavelength, amplitude, period, frequency and wave speed. |
86 | A tuning fork is an instrument used by musicians to create sound waves of a specific frequency |
87 | They are often used to tune musical instruments.Sound waves coming from a tuning fork are caused by the vibrations of the tuning fork which push against the air particles in front of it |
88 | As the air particles are pushed together a compression is formed |
89 | The particles behind the compression move further apart causing a rarefaction |
90 | As the particles continue to push against each other, the sound wave travels through the air |
91 | Due to this motion of the particles, there is a constant variation in the pressure in the air |
92 | This means that in media where the particles are closer together, sound waves will travel faster.Tuning forkSound waves travel faster through liquids, like water, than through the air because water is denser than air (the particles are closer together) |
93 | Sound waves travel faster in solids than in liquids.A sound wave is a pressure wave |
94 | This means that regions of high pressure (compressions) and low pressure (rarefactions) are created as the sound source vibrates |
95 | These compressions and rarefactions arise because the source vibrates longitudinally and the longitudinal motion of air produces pressure fluctuations. |
96 | The most common example of electromagnetic (EM) radiation is visible light |
97 | Everyone is very familiar with light in everyday life, you can only see things because light bounces off them and enters your eyes |
98 | This alone makes it worthwhile to learn about it but there are also very many other applications of EM radiation |
99 | It is called electromagnetic because there are electric and magnetic fields making up the radiation |
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