(credit: modification of work by “Chemicalinterest”/Wikimedia Commons) Copper(II) oxide, a powdery, black compound, results from the combination of two types of atoms-copper (brown spheres) and oxygen (red spheres)-in a 1:1 ratio. In a given compound, the numbers of atoms of each of its elements are always present in the same ratio (see figure below for an example). A compound consists of atoms of two or more elements combined in a small, whole-number ratio. CompoundsĪ pure substance that can be broken down by chemical change into simpler components (because it has more than one element) is a compound. Fun fact: O f the 118 known elements, only about 90 occur naturally on the earth, and two dozen or so have been created in laboratories. If it is depicted on the periodic table, then it is an element. If you are unsure of whether a particular substance is an element, check for its name on the periodic table. You are not expected to be familiar with all of the 118 elements discovered so far, and you are definitely not required to memorize them! You are encouraged to use a periodic table as a tool throughout this class. You may even find a few of these in your kitchen. Some elements may be familiar to you, such as iron, silver, gold, sulfur, oxygen, carbon, and aluminum. (credit: modification of work by “slgckgc”/Flickr) A pre-1982 copper penny (left) contains approximately 3 × 1022 copper atoms (several dozen are represented as brown spheres at the right), each of which has the same chemical properties. Since pure copper is made up of these indivisible atoms, it is classified as an element. A copper atom cannot be broken down into any smaller, simpler particle – an atom is already the smallest particle. (Copper pennies minted before 1982 were pure copper.) A copper penny is made up of many copper atoms. ElementsĪ pure substance that cannot be broken down into simpler substances by physical or chemical changes is an element. In contrast, scientists have identified tens of millions of different compounds to date. Today, there are about 118 elements in the known universe. There are two types of pure substances: elements and compounds. Any sample of sucrose also has the same physical properties, such as melting point, color, and sweetness, regardless of the source from which it is isolated. Any sample of sucrose (table sugar) consists of 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms. All specimens of a pure substance have exactly the same makeup and properties. Pure SubstancesĪ pure substance has a constant composition. Two broad categories are pure substances (including elements and compounds) and mixtures (including heterogeneous mixtures or homogeneous mixtures). The technique used depends on the nature of substances which make up the mixture.Matter can be classified into several categories. Mixtures can be separated by filtration, distillation, crystallisation or chromatography. Unlike elements and compounds, which have fixed melting and boiling points, mixtures will melt and boil over a range of different temperatures, as each component of the mixture will change state at different temperatures. Other examples of mixtures include cake batter and shampoo. Air is a mixture, as it is made up of nitrogen, oxygen and argon (all elements) along with carbon dioxide and water vapour (compounds). MixturesĪ mixture is a group of different elements or compounds which are not chemically bonded together. Examples include carbon dioxide (CO 2), water (H 2O) and ethanol (C 2H 5OH), which are all made up of two or more types of atoms bonded together. CompoundsĬompounds are made up of more than one type of atom chemically bonded together. Notice that all of these things are only made up of a single type of atom. Elements include oxygen molecules (O 2), helium atoms (He) inside party balloons and hydrogen molecules (H 2) in the Sun's core. An easy way to determine whether something is an element is to see if it appears on the Periodic table, as all elements can be found there. An element is a substance made up of only one type of atom.
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