Pretest This will not be graded!!! Do the best you can to help me get an accurate idea of your knowledge.

Atoms Protons- positively charged Neutrons- neutrally charged Electrons- negatively charged Where does an atom’s mass come from? Electrostatic force holds the protons and neutrons together in the nucleus Electrons have 1/1840 the mass of a proton. But what is mass? Atoms have the same number of protons and electrons- therefore the atom is neutral

Elements Element- substance that is made up of only one type of atom Four most common elements in nature include oxygen, nitrogen, carbon, and hydrogen

Isotopes Atoms of an element may have different numbers of neutrons Radioactive isotopes- decay over time at a certain rate Total number of protons and neutrons in the nucleus of an atom is known as its mass number

Chemical Compounds Substance formed by the chemical combination of two or more elements in definite proportions Chemical formulas represent compounds H2O

Ionic Bond Transfer of electrons between atoms

Covalent Bond Sharing of electrons between atoms

Van der Waals Forces Electrons move around a lot and cause temporary positive and negative areas. This can cause a temporary attraction between molecules

Read pg. 39 Connection to Real World What are some situations in which adhesive bandages don’t stay on very well? Why don’t bandages stay on well in these situations? What do doctors typically use to hold together tissues after surgery? Why might bandages be a better alternative?