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Based on certain properties, elements are classified as metals, non-metals, and metalloids.
Based on discoveries of the atomic theory, we can now draw structures for elements. These structures can be shown in Bohr diagrams. To draw Bohr diagrams we need to know the following:
- Protons and neutrons are located in the nucleus, whereas electrons are located in energy shells surrounding the nucleus
- From the atomic number, we can see how many protons an element has. Also the number of protons and the number of electrons are the same in all atoms so that charges are balanced. (For example, chlorine has an atomic number of 17. Therefore, chlorine has 17 protons and 17 electrons.)
- The first shell can hold a maximum number of 2 electrons and every other shell after can hold a maximum number of 8 electrons.
- As a result, the Bohr diagram for chlorine is as followed. 2 electrons in the first shell + 8 electrons in the second shell + 7 remaining electrons in the third shell = 17 electrons total
- The outermost shell is called the valence shell. The electrons in the valence shell are called valence electrons. Therefore, chlorine has 7 valence electrons.
- The amount of valence electrons in an atom can be represented by another diagram called a Lewis Structure. In these diagrams, we only show the amount of electrons in the outermost shell. Below are examples for Cl, Na, and O.
From these discoveries we learned that atoms contain 3 subatomic particles – protons, neutrons, and electrons.
Protons and neutrons are located within the nucleus, whereas electrons are in energy levels surrounding the
nucleus.
Ionic compounds are substances made up of at least one metal and one non-metal. In an ionic compound the metal will form a positive ion and the non-metal will form a negative ion. The positive and negative charges attract each other. For example, table salt is sodium chloride made up of sodium ions and chlorine ions.
When you take an individual element (like gold or carbon) and break it down into its smallest form you get an atom. An atom is the smallest part of an element that has all of the element’s properties. Atoms of different elements have different properties. For example, atoms of copper are not the same as atoms of iron. Throughout many years scientists have developed an atomic theory to study the structure of atoms and how they combine to form matter. You will learn about how different scientists have added to this atomic theory to
become what it is today.
Every language has its own name for each of the elements. For example oxygen in English can be “oxigeno” in
Spanish, “sauerstoff” in German, or “oksiheno” in Filipino. Therefore, to help communication chemists worldwide have agreed to use the same set of symbols of elements. So no matter where you are the symbol for oxygen is O. An element symbol consists of one or two letters. The first letter is always capitalized. If there is a second letter, it is not capitalized.
Matter is a physical substance in general, as distinct from mind and spirit; (in physics) that which occupies space and possesses rest mass, especially as distinct from energy.
When studying chemistry an important tool you will be using is the periodic table. A periodic table like the one below will give you information about different elements. As you can see each box will have the element name
and symbol that we learned about from Activity B.
Molecular compounds are substances created by combining non-metals only. In a molecular compound, atoms share electrons to complete electron shells. For example, a water molecule contains two hydrogen atoms sharing their electrons with one oxygen molecule.
Matter can be classified as a pure substance or a mixture. A pure substance I made up of one kind of matter, whereas a mixture is a combination of different types of matter or pure substances.
We describe matter using characteristics called properties. A physical property is a characteristic of a substance that can be observed or measured. For example, the melting point of water is considered a physical property
A chemical property describes the ability of a substance to change into a new substance or substances. Therefore, to observe a chemical property a reaction has to occur. This reaction is also called a chemical change, which is different from a physical change. In a physical change, the substances involved remain the same substances, even though there may be a change
of state or form. Some examples of physical changes are melting, boiling, freezing, and dissolving. Most physical changes are easy to reverse.