[0:00]Hi everyone, welcome to IGCSE Study Buddy, where you can revise chemistry topics from the Cambridge IGCSE syllabus. If you are enjoying our videos so far, please don't forget to hit the like button and subscribe to our channel. In this video, you are going to learn part one of topic two, Atoms, elements and compounds. First, let's learn about elements, compounds and mixtures. An element is a pure substance made up of only one type of atom. It's the simplest form of matter. Elements are represented by chemical symbols, such as O for oxygen or H for hydrogen. There are about 118 known elements, each with its unique properties. Elements cannot be broken down into simpler substances. An oxygen molecule or O2 is an example of an element. This element is a molecule composed of two oxygen atoms bonded together. So, the element oxygen consists of only oxygen atoms. The element carbon is made of only carbon atoms and so on.
[1:45]Compounds are substances formed when two or more different elements chemically combine. They have distinct and unique properties, different from the elements that make them up. Compounds can be represented by chemical formulas, such as H2O for water or CO2 for carbon dioxide.
[2:15]Compounds cannot be separated physically. Chemical reactions are needed to break compounds into their individual elements. Water and carbon dioxide are examples of compounds. Water or H2O is a compound composed of two hydrogen atoms and one oxygen atom chemically bonded together. Carbon dioxide or CO2 is a compound consisting of one carbon atom bonded to two oxygen atoms. Mixtures are combinations of two or more substances (elements or compounds) physically mixed together but not chemically bonded. The components in a mixture retain their individual properties.
[3:20]They can be separated by physical means, such as filtration or distillation. Example, salt water. When you dissolve table salt or sodium chloride in water, you create a mixture. The salt doesn't chemically combine with water, but is dispersed throughout it. It is common to find the terms atom, molecule and compound somewhat confusing. Let's simplify the distinctions. Atom, think of an atom as the smallest indivisible unit of an element. It's a single type of particle. A molecule is a group of atoms bonded together. Molecules can be made of atoms of the same or different elements. So this is a molecule and these are also molecules.
[4:28]A compound is a specific type of molecule. It consists of atoms of different elements chemically bonded together. So even though this is a molecule, it is not a compound. These are molecules and they are compounds. Not all molecules are compounds. Some molecules consists of atoms of the same element bonded together like O2 or oxygen gas, which is not a compound. Compounds specifically refer to molecules with different elements.
[5:14]So, a substance made up of only one type of atom is called an element. A substance made of two or more different types of atoms is called a compound. A mixture contains two or more elements or compounds that are not chemically bonded together.
[5:43]The differences between elements, compounds and mixtures are: Elements are made of only one type of atom. Compounds are made of two or more different types of atoms. And mixtures contains two or more elements or compounds that are not chemically bonded together. Each element has its unique properties. Compounds have their own unique properties that are different from the elements that make them up.
[6:26]And the components in a mixture keep their individual properties.
[6:34]Elements cannot be broken down into simpler substances. Compounds cannot be separated physically. They can only be separated into elements chemically. Mixtures can be separated physically.
[6:58]Next, let's dive into atomic structure and the periodic table. An atom is the smallest unit of matter that makes up everything around us. Atoms are the basic building blocks of all substances and come in different types known as elements, such as carbon, hydrogen and oxygen. An atom has a center called the nucleus with neutrons and protons, and around this center, there are electrons arranged in energy levels or shells. These electrons orbit the nucleus. Atoms consist of subatomic particles known as: Protons, Neutrons, and Electrons.
[8:04]So the key features of atoms are: Nucleus: The nucleus is the central core of an atom.
[8:18]It contains two types of subatomic particles - Protons - Positively charged particles, Neutrons - Electrically neutral particles (no charge) also located in the nucleus. Electrons are negatively charged particles that orbit the nucleus in specific energy levels or shells. They are much lighter than protons and neutrons.
[8:52]Electron Shells: Electrons are arranged in energy levels or electron shells around the nucleus.
[9:03]These shells can hold specific numbers of electrons, with the innermost shell having the lowest energy and subsequent shells having higher energy levels. Let's take a look at the relative charges and masses of subatomic particles. Protons are located in the nucleus of an atom. They have a relative charge of +1 or positive charge.
[9:36]Their relative mass is approximately 1 atomic mass unit or amu. Neutrons are also located in the nucleus. They have zero relative charge or neutral or no charge.
[9:57]Their relative mass is also approximately 1 atomic mass unit. Electrons are located in the shells. They have a relative charge of -1 or a negative charge. Their relative mass is approximately 1/1836, which is so small that it's often considered zero or negligible.
[10:33]The proton number or atomic number is the number of protons in the nucleus of an atom.
[10:42]The atomic number is represented by the symbol Z. The number of protons will always be equal to the number of electrons in a neutral atom.
[10:59]The atomic number also helps us identify where the element is located on the periodic table.
[11:10]Each type of atom is characterized by its unique number of protons, that is what is known as the atomic number. For example, all atoms with six protons are carbon atoms.
[11:29]Please note that on some periodic tables, the numbers may be arranged differently. But remember that the atomic number is the smaller of the two numbers, whether it's at the top or the bottom. The mass number or nucleon number is the total number of protons and neutrons in the nucleus of an atom.
[11:58]It represents the total mass of the atom. The mass number is represented by the symbol A. Mass number or nucleon number is equal to the number of protons plus the number of neutrons.
[12:20]The periodic table provided in your exam lists elements with their atomic number at the top and the relative atomic mass at the bottom. Please note that the relative atomic mass is not the same thing as mass number.
[12:45]The relative atomic mass is the average mass of all the isotopes of an element. While the mass number is the total number of protons and neutrons in an atom's nucleus.
[13:03]Since each proton and neutron has an atomic mass unit of 1, the mass number of each element is very close to the relative atomic mass of that element. Relative atomic mass is often expressed as decimal numbers, but for simplicity, except for chlorine, it is rounded to the nearest whole number, making it look like the mass number. Even though they don't mean the same thing, for most cases in your exam, you can use relative atomic mass as a substitute for mass number, except for chlorine.
[13:49]For example, take carbon 12. Its relative atomic mass is actually 12.011, but it has been rounded to the nearest whole number, so it's 12. The mass number of carbon 12 is also 12.
[14:12]So you can use the relative atomic mass as the mass number. We can find the number of neutrons in an atom using a simple calculation. Let's take the element carbon as an example. We know that it has six protons, since its atomic number is 6. We know that it has six electrons, since the number of protons equals to the number of electrons. So, how do we find the number of neutrons? Since the mass number is the total number of protons and neutrons, if we take away the number of protons from the mass number, we will be left with the number of neutrons. So for this example, the mass number is 12. Take away the number of protons six equals six, which is the number of neutrons. That concludes part one of topic two, Atoms, elements and compounds. Are you enjoying our videos? Are they helping you? Here's a way you can show your appreciation and support our continued efforts. You may use YouTube Super Thanks to send us thanks.
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