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Combinations of Atoms September 3, 2009 Compounds • When the atoms of more than one element combine, they form a compound. Examples: Water (H20)= 2 Hydrogen+ 1 Oxygen Salt (NaCl)= 1 Sodium+ 1 Chloride Sugar (C12H22O11)= 12 Carbon+22 Hydrogen+ 11 Oxygen How do compounds form? When atoms chemically bond together they form a compound by sharing or exchanging electrons. We are going to look at 4 types of chemical bonds. Covalent Bonds • This type of bond is when atoms SHARE an electron. A group of atoms connected by covalent bonds are called molecules. Example: Water! The 1 oxygen atom shares its electrons with the 2 hydrogen atoms. Ionic Bonds • When atoms are electrically charged they are called ions. If the atom have more electrons than protons then the atom is negatively charged. If the atom has more protons than electrons then the atom is positively charged. Sodium ion (+) Chloride ion (-) Ionic Bonds Continued • Ions of opposite charges are attracted to each other. (similar to magnets) So the Sodium (Na) Ion (+) attracts the Chloride (Cl) Ion(-) and they form an ionic bond which no longer has a charge. NaCl is made, which is SALT! http://www.youtube.com/watch?v=yjge1WdCFP s Metallic Bonds • These bonds are found in metals such as copper, gold, aluminum, and silver. These bonds allow the electrons to move freely which makes them easily pass an electric current through them. Steel: Bonding iron and carbon Brass: Bonding copper and zinc Hydrogen bonds • These bonds form without any interaction of electrons. These bonds are very important to everyday life: showering, boiling vegetables, making tea, and riding on a boat. Examples: penny and dropper paper clip and petri dish Mixtures • Combining 2 or more substances that are not chemically combined. Think of a salad! Heterogeneous mixtures • These mixtures are not mixed evenly and each part keeps its own properties. Salads are great examples of heterogeneous mixtures! Homogenous mixtures • Mixtures that are evenly mixed. You can’t see the parts anymore. Another name for this type of mixture is a solution. Ocean water (salt and water)is a great example! Separating Mixtures and Compounds • You can physically separate mixtures. Try picking out the carrots, lettuce, and tomatoes out of a salad. When you let ocean water evaporate in a cup you have salt left. (EASY) • Compounds must be separated by chemical means. Example: C12H22O11 (sugar)+ H2SO4 (sulfuric acid) The sulfuric acid removes water from the sugar, which releases heat, steam, and sulfur oxide fumes. All that is left of the compound is carbon.
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