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- All living organisms are built of matter composed of atoms and molecules.
- Matter is everything with mass and volumee.
- Atoms are the building blocks of all mattter. Each atom has a central nucleus containing protons and neutrons, surrounded by a cloud of electrons. Atoms can lose or gain electrons and become electrically charged, (ionized) or they can share electrons.
- - Electrons are arranged in orbitals (shells) at different energy levels and distances from the nucleus.
- Shell #1 can hold 2 electrons
- Shells #2 and #3 can hold 8 electrons each
- Shells #4 and #5 can hold 18 electrons each
- A full outer shell means a stable configuration
(drawing of atom and charge)
- - Electrically charged atoms are called ions.
- Metallic elements tend to lose electrons to form positive ions.
- Nonmetals tend to gain electrons and form positive ions.
- Pure elements contain only one type of attom. Each element has a different atomic structure containing a specific number of protons. Elements are represented by a chemical symbol which contains one or two letters.
- Most living things are composed of the saame chemical elements and perform similar biochemical reactions.
- A compound has two or more elements chemiically combined in a specific ratio which is represented by a chemical formula.
ex H2O, CO2
- The smallest particle of any compound is called a molecule. Positive and negative ions attract one another to form ionic compounds. Atoms that share electrons form covalent compounds. Organic compounds are compounds that contain covalently bonded carbon.
- A chemical equation represents a chemicall reaction or a chemical change in one or more compounds.
ex. CO2 + H2O ------> C6H12O6 + O2
- A pH scale is used to indicate the degreee of acidity (concentration of hydrogen ions) or the degree of alkalinity (concentration of hydroxide ions) of a particular solution. This scale ranges from 0 to 14 with a pH of 7 representing equal concentrations of hydroxide and hydrogen ions.
pH < 7 is acidic
pH > 7 is basic
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