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Compounds and Molecules

Compounds and Molecules. When two elements combine chemically it is called a compound. What is a compound?. How do you know how much of an element is in a compound?.

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Compounds and Molecules

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  1. Compounds and Molecules

  2. When two elements combine chemically it is called a compound. What is a compound? How do you know how much of an element is in a compound? The number after the symbol in a compound tells the number of those elements in the compound. H2O – two hydrogen and one oxygen – 2:1 Elements combine with the same or different elements in order to fill their outer-most shell(orbit). Why do elements combine? Elements in the 18th column have all their orbits full. They are the noble gasses and rarely combine with other elements. What is special about noble gasses?

  3. Chemical Bonds

  4. What is a covalent bond? When elements share electrons to make a compound, it is called a covalent bond. What kind of bond forms when an element “steals” electrons from another element? When one element “steals” electrons from another element to make a compound, it is called an ionic bond. When two or more elements combine forming covalent bonds they are called molecules. What is a molecule? The ionic charge tells how many electrons an element wants to “take”, “give away”, or “share”. What does the ionic charge tell you about an element? Transition metals are elements that do not fill out their orbits from the inside out. They fill them however they like, but they can not overfill an orbit. What is a transition metal?

  5. Chemical Reactions

  6. A Synthesis reaction involves two separate things joining to form one compound. 4Fe + 3O2 2Fe2O3 What is a synthesis reaction? A Replacement reaction takes place when elements switch or replace each other. 2AgCl + Pb  PbCl2 + 2Ag What is a replacement reaction? A Decomposition reaction is a breaking down of a more complex substance into two simpler substances. H2CO3 CO2 + H2O What is a decomposition reaction?

  7. Kinds of Compounds Acids contain the element hydrogen, have a sour taste – HCl. What is an acid? What compound has a bitter taste and is slippery? Bases contain the elements oxygen and hydrogen, have a bitter taste, and feel slippery – NaOH. An indicator is something that changes color in the presence of an acid or base: Litmus and pH paper. What is an indicator? Blue litmus turns red in an acid. Red litmus turns blue in a base. pH paper has a color coded scale from 1-14, 1 being the strongest acid and 14 the strongest base. How can you tell if a substance is an acid or a base?

  8. A substance that is neither an acid nor a base is a neutral - 7 on pH scale. What is the pH of a neutral substance? When an acid and a base combine chemically salt and water forms. How do you make a salt? The process of combining an acid and a base is called neutralization. NaOH + HCl  NaCl + H2O sodium hydroxide+hydrochloric acid salt+water What is it called when you add an acid to a base? When oxygen combines with another element it forms an oxide. What is an oxide?

  9. Chemical reactions that give off heat, or energy, are called exothermic reaction. What is an exothermic reaction? Chemical reactions that absorb energy are called endothermic reactions. What are reactions that absorb energy called?

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