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what are physical and chemical changes?
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physical changes are the substances that don't change and chemical changes are the substances that change
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why do elements combine to form chemical bonds?
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because most of them are not stable
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which ones are stable? What makes them stable?
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the noble gases. The number of electrons they have
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caracteristics of ionic bonds
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-they are formed by a metal atom ( with a tendency to lose electrons ) and a non-metal atom ( with a tendency to gain)
-the metal is going to lose electrons in order to became stable, forming a positive ion -the non-metal gains electrons, forming a negative ion -the atoms attract each other and form an ionic compound -ionic compounds are always crystals (lattices) |
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caracteristics of covalent bonds
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-they are formed by two metals (with a tendency to gain electrons)
-they share electrons. Per each electron they share, they gain one that is shared by another atom -they remain together because they are shearing electrons -covalent compounds can form molecules or crystals |
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what are chemical reactions used for?
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-to create new substances
-to get rid of substances we don't want -to obtain energy |
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what changes and what doesn't during a chemical reaction?
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don't change change
-elements -chemical bonds -the number of atom. -substances of each element. -some chemical reactions -the mass. produce energy and some need energy to take place |
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what are the reactants? And the products?
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the reactants are the substances you have before the chemical reaction and the products are the substances you have after the chemical reaction
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what are endothermic reactions and the exothermic reactions?
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the endothermic reactions need energy to take place and the exothermic reactions produce energy when they take place
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