Chapter 2 Notes
Chapter 2 Notes BIOS 103 Introduction to Biological Sciences
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This 3 page Class Notes was uploaded by Jessica Keller on Monday August 29, 2016. The Class Notes belongs to BIOS 103 Introduction to Biological Sciences at Northern Illinois University taught by Dr. Stoia in Fall 2016. Since its upload, it has received 11 views.
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Date Created: 08/29/16
Chapter 2 2.1 Chemical Elements Matter: Anything that has mass and occupies space - Solid - Liquid - Gas Made of elements Element is a substance that cannot be broken down into substances with different properties Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur Atoms Atom: is the smallest part of an element that displays the property of the element. Composed of subatomic particles: protons, neutrons, electrons Central nucleus • Protons – positively charged, 1 amu • Neutrons – no charge, 1 amu Orbiting clouds around nucleus (electron shells) • Electrons – negatively charged, very low mass-negligible in calculations Atomic Number Each element is represented by one or two letters to give it a unique atomic symbol. H = hydrogen, Na = sodium, C = carbon The atomic number is equal to the number of protons in each atom of an element. The mass number of an atom is equal to the sum of the number of protons and neutrons in atom’s nucleus. The atomic mass is approximately equal to the mass number. Isotopes Isotopes are atoms of the same element that differ in the number of neutrons (and therefore different atomic masses). Electrons and Energy • Electrons are attracted to the positively charged nucleus; thus, it takes energy to hold electrons in place. • It takes energy to push them away and keep them in their own shell. The more distant the shell, the more energy it takes to hold in place. • Electrons have energy due to their relative position (potential energy). • Electrons determine chemical behavior of atoms. Valence Electrons • Tvalence shell.nergy shell of any atom is called the • The valence shell is important because it determines many of an atom’s chemical properties. • The octet rule states that the outermost shell is most stable when it has eight electrons. Exception: If an atom has only one shell, the has two electrons.shell is complete when it 2.2 Molecules and Compounds • A molecule is two or more elements bonded together. It is the smallest part of a compound that retains its chemical properties. • NaCl, H2, etc. • A compound is a molecule containing at least two different elements bonded together. CO 2 H 2, C 6 12 6 , etc. • A formula tells the number of each kind of atom in a molecule. C 6 12 6means there is one molecule of glucose containing 6C,12H, 6O. Chemical bonding • Bonds that exist between atoms in molecules contain energy. • Bonds between atoms are caused by the interactions between electrons in outermost energy shells. • The process of bond formation is called a chemical reaction.
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