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Chemistry: Parts of an Atom. The smallest, basic building blocks of all matter! CELLS: LIFE :: ATOMS: MATTER. Properties of an Atom. Element - substance that cannot be broken down into other substances by chemical or physical means
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Chemistry: Parts of an Atom The smallest, basic building blocks of all matter! CELLS: LIFE :: ATOMS: MATTER
Properties of an Atom • Element - substance that cannot be broken down into other substances by chemical or physical means • Atom - the smallest particle of an element and is made of a nucleus surrounded by one or more electrons • How is a molecule & compound different?
Molecules vs. Compounds • Molecule-two or more atoms chemically combined ex. O2 or H2 • Compound-atoms of two or more elements combined chemically ex. CO2 or H2O
Structure and Composition • Nucleus - the tiny central core of an atom that is made up of particles called protons and neutrons • Protons - have a positive electric charge (+) • Neutrons - have no charge; they are neutral • Electrons - a third type of particle that has a negative charge (-) and moves rapidly in the space around the outside of the nucleus • An atom is neutral or stable when it contains equal numbers of protons and electrons.
Model of Nitrogen http://www.csmate.colostate.edu/cltw/cohortpages/viney/atomhistory.html
Atomic Number and Atomic Mass • atomic number - the number of protons in an atom’s nucleus; an element’s identity • Example: Every carbon atom contains six protons, therefore carbon’s atomic number is six • atomic mass - the number of protons plus the number of neutrons found in the nucleus of an atom • Example: An atom that contains 6 protons and 6 neutrons has an atom mass of 12
Role of Electrons • Most of an atom’s mass comes from its protons and neutrons. • Electrons are about 2000 times smaller than protons or neutrons. • But most of an atom’s volume is the space in which the electrons move.
Atom Structure • Nucleus-protons & neutrons • Electron Cloud-orbitals or electron shells • 1st orbital-only 2 electrons • 2nd orbital-8 electrons • 3rd orbital-8 electrons • 4th orbital-8 electrons
Valence Electrons • valence electrons - the electrons farthest away from the nucleus and most loosely held to the atom; the number of valence electrons determines an element’s properties-specifically its reactivity • chemical bond - the force that holds atoms together • When chemical bonds form, valence electrons are either transferred or shared between atoms.
Electron Dot Diagram • electron dot diagram - made up of the symbol for an element surrounded by dots. • Each dot stands for one valence electron. http://www.iun.edu/~cpanhd/C101webnotes/chemical-bond/lewis-electron-dot.html