[0:04]Hello. So, today we will study about Chemistry Form 4, Chapter 2, the structure of the atom. So, the first thing that you need to know in this chapter is matter. So, we actually have to understand what matter really is. So, actually, everything around us is made up of matter. This piece of paper is made up of matter. My pen is made up of matter and every all the air around you is also made up of matter. So, by definition matter is actually anything that occupies space and has mass. Matter is anything that occupies space and has mass and this matter is actually made up of tiny and discrete particles. For example, the air is made up of matter but you can't actually see the particles of air with your eye. It is made up this is because it is made up of tiny and discrete particles. And these particles can be in the three forms, it can be in three forms, which is atoms. molecules and ions. So atoms are the simplest type of particles because it only exists in its own. It's only one, right? Like a zinc atom. So, it's only one. But molecules, they are made up of two or more of these atoms. For example, an example of a molecule is carbon dioxide. Or CO2 which is made up of one carbon and two oxygen. Right? And these molecules are neutral. They do not have charges. But for ions, ions are actually charged particles. And these charged particles can either be a positively charged particle, or a negatively charged. So, if it's positively charged, it's called a cation and if it's negatively charged, it's called an anion. And to remember which is positive and which is negative is very simple. As you can see, cation has a T here. So, you can use this T to remember T is equal to positive. So, positive is a positive charged ion. And for anion, you can see that there's an N, so you can remember N for negative. And in this chapter, we have we are going to use a few terms. The first term is element. The second term is compound and the third term is mixture. So, an element is only made up of one type of atom. And for compound, compound is made up of two or more elements combined together chemically. This means that they cannot be separated physically. For example, mixture is the same thing, but it's not chemically, it's physically. An example of a mixture is when you mix Milo powder in water to produce a Milo drink. And if you let it sit for a few hours, the Milo powder might actually drop to the bottom. So, it can actually be separated because it's physically combined. But for a compound, it's chemically combined and it won't it won't break break down over time. For example, table salt or NaCl. Sodium chloride, table salt. The salt will always be salt. It won't it won't become sodium and chloride on its own because they're chemically combined unless you react it with another substance to actually break it up. And these compounds, there are two types of compounds. There are two types of compounds which are ionic compounds and covalent compounds. Ionic compounds are made of ions and covalent compounds are made of neutral molecules.
[4:50]So, this is part one of Chemistry Form 4, Chapter 2. So, the first thing that you need to know is matter. Matter is anything that occupies space and has mass and it is made up of tiny and discrete particles. And these particles are divided into atoms, molecules and ions. And the and the ions are charged particles which can either be positively charged or negatively charged. The positively charged ions are called cations. The negatively charged ions are called anions. And element is the simplest substance. It is only made up of one type of atom. Compound is made up of two or more elements combined together chemically. Mixture is two or more elements combined together physically. And the compounds can either be ionic compounds that are made of ions or covalent compounds that are made of neutral molecules. Next, we will learn about the states of matter. So, these particles can exist in three forms, which is solid, liquid and gas. And these and an example of a solid is this piece of paper is solid. And an example of a liquid is water and example of gas is all is the air around you. So, the arrangement of the particles in solid is that they look like this, right?
[6:05]So, the particles are closely arranged or packed closely together in an orderly manner. But for liquids, they are also kind of closely arranged together but there are a lot of spaces between the particles as compared to solids. And the gas particles are very far apart from each other. So, the solid particles, they are packed closely together in an orderly manner. And for liquids, there are they are also packed closely together but there are a lot of spaces between the particles. And for gas, the particles are very far apart. So, why why are the particles in a solid packed closely together? It is because they have very they have very strong forces of attraction.
[7:20]And for liquid, they also have quite strong but they are weaker than solids. And for gas, it is very weak. And the solids for movement, the gas, since the forces of attraction are very weak, they actually move about randomly in all directions. And for liquids, they move about in their positions. And for solids, they do not move. They vibrate at their fixed positions. And these solids, liquids and gas, they can actually change from one state to another. Meaning that a solid can change to a liquid and a liquid can change to a gas. Or a gas could also change to a liquid and a liquid could also change to a solid. And a solid could change to gas and a gas could change to solid.
[8:44]So, the process by which a solid becomes a liquid is actually melting. And the process by which a liquid becomes a gas is evaporation or boiling. And the process by which a gas becomes a liquid is condensation. And the process by which a liquid becomes a solid is freezing. And a solid could also become a gas without becoming a liquid and this process is known as sublimation. And the process by which a gas becomes a solid is also known as sublimation.
[9:37]And in Form 4, we actually learn about an experiment to determine the melting point and also the freezing point of naphthalene. And the the setup of the apparatus of the experiment look something like this. So, this is the one for heating and this is the one for cooling. This is the thermometer. This is the naphthalene. This is a water bath. And this is actually a conical flask. And we oh oh, one more thing is that if during heating and cooling, we actually use the thermometer to stir the naphthalene. And this is to also ensure even heating and cooling. So, we put this also to ensure that it cools evenly. And in this experiment, if And during this experiment, if you realized uh when you are taking the readings for the temperature at 30-second intervals, you will notice that the temperature of the naphthalene increases. But at some point it remains constant. For example, if you started heating at 27 degree Celsius, it will increase to 32, 34 and etc. And then it reaches a point where uh at 69 degrees or 79 or 71 degrees, it stays constant for like two minutes or three minutes. So, it will be 71, 71. And when you plot the graph, when you plot the graph of temperature against time, what the graph you will get is something like this. So, what actually happens at this point when the temperature is constant is that the naphthalene is actually melting. That that is the melting point of naphthalene. So, at this point until this point, there are both solid and liquid particles. And at this point, And when you do this experiment, you will realize that when you are recording the temperature at 30-second intervals, you will realize that the temperature increases. For example, if and and it suddenly remains constant. For example, if you start heating at 27 degrees, it will increase to 32 degrees, uh 34 degree Celsius and then it suddenly remains constant like 69 or 70 or 71. So, you'll see that the temperature stays constant at 71 degrees for around two minutes or so. So, during that time, if you if you actually plot the graph, if you draw the graph of uh temperature against time, you will realize that the graph looks something like this. So, during this constant temperature, the naphthalene is actually melting. That is actually the melting point of naphthalene. So, during this time, from this point to this point, both solid particles and liquid particles are present. But at this point, there are only solid particles and at this point there are only liquid particles. So, during the melting point, the reason why the temperature remains constant is because the particles, the solid particles, the the solid particles, right? So, when the temperature increases, the heat energy that is absorbed is not used to increase the kinetic energy, but the heat energy absorbed is actually used to overcome the forces of attraction.
[4:34]Between the solid particles to change states of matter to liquid particles. And at this point to this point, the heat energy increases the kinetic energy of the particles and the particles will vibrate faster. And at this point, the temperature when the temperature increases, the kinetic energy also increases. And for this experiment, when you draw the graph of temperature against time, the graph looks something like this. And the explanation is almost the same. Over here, it's only liquid. Here is solid and liquid. And here it is solid. So, this is the freezing point of naphthalene. And at this point, it's not that the heat energy absorbed is overcome is used to overcome the forces of attraction, but it is that the energy the heat energy released is exactly balanced by the heat liberated as the forces of attraction pulls the liquid particles together to form a solid. Yeah. So, at this point, the temperature remains constant because the heat energy released is exactly balanced by the heat energy liberated as the forces of attraction pulls the liquid particles together to form a solid. And over here, the temperature decreases. When the temperature decreases, the kinetic energy of the liquid particles decreases. And over here, same thing. Right? Next, we will learn about the structure of the atom. So, the structure of the atom looks like this. So, the middle part is called the nucleus, which consists of the protons and the neutrons. And these are called the shells and the orbiting things at the shells are called the electrons. The protons are positively charged, the electrons are negatively charged and the neutrons are neutral. They do not have a charge. And in an atom, usually, the proton number is equal to the electron number. And the and if, for example, an electron has been released. Then if an electron has been released, it makes that the number of electrons is less than the protons. And that means that it will that means that the proton is more than the electron.
[7:50]And when proton is more than electron, proton is positively charged, electron is negatively charged. So, the positive charge is much more powerful than the negative charge. Then this atom becomes a positively charged ion, which is a cation. But if a electron is accepted, then proton is less than electron. And since electron is negatively charged, if there is more electrons, it becomes an anion, which is a negatively charged ion. And the number of protons and neutrons is actually called the nucleon number.
[8:47]The nucleon number. Nucleon number is the number of the total number of protons and neutrons in the nucleus of an atom. The nucleon number is the total number of protons and neutrons in the nucleus of an atom. And if two atoms have the same proton number, but different nucleon number because of different neutron number, then they are known as isotopes. Isotopes are elements which have the same proton number but different nucleon number because of different neutron numbers. So, isotopes have the same chemical properties. The chemical properties are determined by the electrons. So, if they ask why do two of two elements have the same chemical properties? Your answer would be that they have the same valence electron. And that's all. To recap, for electron arrangement or atomic structure, the rules that you have to know is that the first shell has two electrons, the second shell has eight electrons, third shell has eight electrons. Fourth has also eight and so on. And so, if for example, sodium has 11 protons, it also has 11 electrons. So, that would be 281. And then this is how you draw the atomic structure or electron arrangement. And if in the case it wants to be stable, it will release one electron to achieve stable electron arrangement or to be more precise, it will be octet electron arrangement. And if it does remove or release one electron to achieve stable electron arrangement, then it will look like this because it has released one electron. And since it releases one electron, it has one proton more than the electrons, which means the charge is positive one or or just positive because we don't write the one. And for magnesium, it's the same thing. It has 12 protons as stated here, which means it has 12 electrons. And if it wants to achieve stable electron arrangement then it will release the two valence electrons to become to achieve stable octet electron arrangement. And when it does, then it will become like this. And since it releases two electrons, it has two protons more than the electrons, which makes the charge 2+. And so, that's all for Chemistry Form 4, Chapter 2. Done.
