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Some elements can have molecules as
their smallest component
as long as the molecule is made up entirely of the same atom The oxygen we breathe is not 1 oxygen atom, it is O 2 When 2 atoms are joined like in the above case, it is called a diatomic element The 7 diatomic elements are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine
Allotropes
allotrope -one of the different molecular forms of an element oxygen has 2 allotropes O 2 and O 3 (ozone) carbon has several allotropes graphite, diamond, buckyball (found in soot)
Mixtures
compounds and/or elements mixed together but not bonded together heterogeneous mixture- different throughout or chunky granite, orange juice with pulp, Italian dressing homogeneous mixture- even throughout milk and saltwater Solution really well mixed homogeneous mixtures
Breakdown of classification
Element atoms Compound molecules Pure substance all the same Solution Homogeneous same Heterogeneous different Mixture Matter
Law of conservation of energy
Energy can neither be created nor destroyed, it can only change forms. An exothermic reaction releases energy, where did it come from? The energy holding the molecules of the reactants together (bonds). The products need less energy to be held together so the energy is released to the area surrounding the reaction. Endothermic reactions absorb energy, where does that come from? ~from the area surrounding the reaction. That is why it ends up feeling colder. In both cases energy is conserved, it is either donated to another system or taken from another system.
Energy Changes
All chemical reactions (chemical changes) involve a change in energy Physical changes also involve a change in energy We are only going to look at phase changes
Heat energy
Atoms/molecules in a substance are not stationary, they move around. Heat energy in an object is the rate of motion of atoms/molecules in a substance The faster the particles are moving the more heat energy the substance has.
Energy in phases
Solid- atoms/molecules vibrate in one place, occasionally sliding by one another. ~students in detention Liquid- atoms/molecules move freely with more energy within a confined volume. ~students in the cafeteria Gas- atoms/molecules move around wildly constantly running into each other. ~football practice
Causing phase changes
To go from solid liquid gas you… add energy (from another system) to turn ice into water you heat it, to turn water to steam you heat it. To go in the reverse direction you remove energy. (there is no cold energy you can add)
