Lecture1BSC2010.pdf

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Department
Biology - Biological Sciences
Course
BSC 2010
Professor
Oppenheimer
Semester
Summer

Description
Lecture 1 Concept 2.1 Atomic Structure is the Basis for Life’s Chemistry ● Living and nonliving matter is composed of atoms. ● Like charges repel; different charges attract. ● Most atoms are neutral because the number of electrons equals the number of protons. ● Dalton—mass of one proton or neutron ●  (1.7 × 10–24 grams) ● Mass of electrons is so tiny, it is usually ignored. ● Element—pure substance that contains only one kind of ● atom ● Living things are mostly composed of 6 elements: Carbon (C) Hydrogen (H) Nitrogen (N) Oxygen (O) Phosphorus (P) Sulfur (S) ● The number of protons identifies an element. ● Number of protons = atomic number ● For electrical neutrality, # protons = # electrons. ● Mass number—total number of protons + neutrons ● Behavior of electrons determines whether a chemical bond will form and what shape the bond will have. ● Atoms with unfilled outer shells tend to undergo chemical reactions to fill their outer shells. ● They can attain stability by sharing electrons with other atoms or by losing or gaining electrons. ● The atoms are then bonded together into molecules. ● Octet rule—atoms with at least two electron shells form stable molecules so they have eight electrons in their shells. Concept 2.2 Atoms interact and Form Molecules ● A Chemical bond is an attractive force that links atoms together to form molecules. ● There are several kinds of chemical bonds. ● Ions are charged particle that form when an atom gains or loses one or more electrons. Cations—positively charged ions Anions—negatively charged ions ● Ionic bonds result from the electrical attraction between ions with opposite charges. ● The resulting molecules are called salts ● Ionic attractions are weak, so salts dissolve easily in water, ● Covalent bonds form when two atoms share pairs of electrons. ● The atoms attain stability by having full outer shells. ● Each atom contributes one member of the electron pair. ● Carbon atoms have four electrons in the outer shell—they can form covalent bonds with four other atoms. ● Properties of molecules are influenced by characteristics of the covalent bonds: These characteristics include: ● Orientation ● Strength and stability ● Multiple bonds ● Degree of sharing electrons ●
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