Chemistry is the study of matter and the changes it undergoes. When you think about chemistry, you think about atoms, which are the "building blocks," or smallest units of matter. Within atoms, there are the subatomic particles, electrons, neutrons, and protons.
Electrons have negative charges, protons positive charges, and neutrons no charge. These are not considered the smallest units of matter since a separate electron particle does not hold the same properties as an atom does. In addition, only the protons and neutrons are held inside the atomic nucleus, and the mass of the two particles combined is considered the mass number. The mass of an electron is so small, about one-two-thousandths the mass of a proton, so it does not really affect the mass number. On the other hand, the atomic mass is the average mass of all isotopes of a specific element.
An element is a substance that cannot be broken down into simpler substances. When you see an atom, it is an atom of one of the elements. You can think of a factory, and as a toy dinosaur as an atom. What color it is painted shows which element it is. An element is distinguished by the number of protons that it has. However, an element can have varying numbers of protons. Isotopes are the different forms of a certain element. For example, you can have 12-carbon, or carbon with a mass number of 12 amu (atomic mass units, which are used in relative measurements), and 10-carbon, or carbon with a mass number of 10 amu.
Some isotopes are more unstable than others and undergo radioactive decay.
Some atoms of an element exist naturally as diatomic molecules, or molecules with two atoms. The elements are hydrogen, nitrogen, oxygen, fluorine, bromine, chlorine and iodine. If you have trouble memorizing these atoms, which will help you in the future if you are thinking of taking chemistry classes that involve you working on chemical equations, then try this acronym: Professor Brinclhof (Buh-rih-n-kul-hof).
Substances can be divided into different categories. Pure substances can be either a compound, a substance made up of two or more atoms of different elements chemically and uniformly combined, or an element. Mixtures are combinations of two or more substances through physical means, so the substances can always be separated through physical means. For beginners, all you need to know is that there are two types: heterogeneous and homogeneous.
Lastly, ions are charged forms of an atom. Normally the number of protons are equal to the number of electrons, so an atom is neutrally charged. However, when reacting with other atoms, they can lose an electron from their electron cloud, or the space around the nucleus where electrons zoom about, and give it to another atom. An atom receives an electron when it needs one to complete its electron orbit. To put it simply, electrons occupy different energy rings around the nucleus, increasing in energy levels the farther away from the nucleus they are (in order for an electron to get farther from the nucleus, it needs to increase its energy to overcome the attraction it has to the positive nucleus). In a beginner's class, you are taught that an atom needs eight electrons on its highest orbit. An atom always wants to be balanced, so when, for example, a potassium ion has an extra electron and a chlorine ion needs one more electron, then the electron transfers. When it transfers, something called an ionic bond forms. It is a bond between ions. Usually metals and nonmetals form those because metals tend to have electrons to spare. A hint for the periodic table: When an element is closer to the left side, it usually means that it has less than four valence electrons, or electrons on its highest energy orbit. When you reach carbon's group, they have four valence electrons, so they can either lose or take electrons. The noble gases, or the last group to the right, are never expected to react because they have eight electrons already and are considered balanced. Molecules are made through covalent bonds between nonmetals because instead of transferring electrons, they share them so that electrons can complete multiple orbits without belonging to one atom specifically. It is sort of like three people huddling in one jacket. Covalent bonds are stronger than ionic bonds because of its "sharing" characteristics.
If you are interested in organic chemistry, which focuses on the study of organic compounds, or compounds containing carbon (carbon is very important in organic chemistry because, for one, of its super ability to bond, and it is seen in all known compounds and molecules concerning life), check out this link. And this one. Or this one. Or buy a book. Books are wonderful.
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