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This 0 page Class Notes was uploaded by Shira Clements on Wednesday February 17, 2016. The Class Notes belongs to BSCI105 at University of Maryland taught by Norma Allewell in Fall 2015. Since its upload, it has received 12 views. For similar materials see Principles of Biology I in Biology at University of Maryland.
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Date Created: 02/17/16
Shira Clements BSC105 Chapter 2 anything that has mass and takes up space cant be destroyed Made up of cannot be broken down chemically atoms of same kind some are toxic two or more elements in xed ratio Essential Elements out of 92 elements only 2025 are essential ones Elements an organism needs to have a healthy life Humans need 25 and plants need 17 C O H N make up 96 of living matter while Ca P K S make up most of 4 Trace Elements elements required by organisms but in low quantity otherwise harmful smallest unit of matter that has same properties of elements Consists of mostly empty smaller narts Cllhatomic particles h 1 Dalton both 0 Neutrons no charge lcleus center of o Protons positive Chi o Electrons negative Lllalyc weighs close to nothing forms negative cloud around nucleus which keeps electrons there because of attraction with opposite charge Atomic Number number of protons unique to element which equals the number of electrons so atoms have no charge Mass Number sum of protons and neutrons o Neutrons can be found by mass atomic lsotopes atoms of same element that have different number of neutrons all have same protons so mass changes 0 Stable ones nuclei do not have tendency to lose particles 0 Radioactive isotope where nucleus decays spontaneously giving off energy and particles which transforms elements to a different one because it loses protons Electrons only electrons are involved in chemical reactions Energy capacity to cause change 0 Potential energy energy matter posses because of its location or structure Atoms want to move to lowest state of potential just like humans and then to build up potential energy again they must do work More distant to electrons are from nucleus the potential energy they have because it is normal for them to be closer o Cant be in between energy levels Found in electron shells each with characteristic and energy level 0 First shell is closer to nucleus so less potential energy and then greater from there 0 Can move between shells as long as it absorbs or loses same amount of potential energy it had previously When absorbs energy goes to shell farther from nucleus When loses energy it goes to shell closer and gives off energy into environment Number of electrons in valence shell outer most determines chemical behavior 0 All atoms with same of electrons in valance act chemically the same 0 lnert elements elements that have full valence shells so chemically unreactive 0 First shell can only hold 2 electrons ls second can hold 8 2p Orbital 3D space where electrons are found usually component of electron shell 0 Only 2 electrons can occupy 1 orbital 1st shell 1 orbital 2ml 4 orbitals interactions that force atoms to stay close to one another either share or transfer electrons to one another Covalent bonds sharing a pair of valence electrons by two atoms wants to make valence shell complete very strong 0 Hydrogen atoms are covalently bonded together each have one atom in valence shell so to make it complete they share the electrons o Creates a molecule H2 means that there are 2 Hydrogen molecules CH4 methane 0 Single bond represented by one line just one pair of electrons shared 0 Double bond represent by two lines two pairs of electrons shared 02 Electronegativity attraction of electrons in atoms the stronger it pulls shared electrons toward atom in covalent the electrons are shared equally because electronegativity of both atoms are equal making it nonpolar H20 but when an atoms bonds to more electronegative atom it is polar one with charge and not shared equally electrons spend more time near one than other giving one a partial negative charge and a partial positive charge 0 O is one of mot electronegative atoms out there when one atom is so much more electronegative than other that it strips other atoms away NaCl but it takes all atoms from incomplete valence leaving it with a complete shell of inner shell teach other 39eate an lOHd NaCl n charged atom weak in water 0 Cation positive charged loses electron o Anion negative charge gains electron attraction between hydrogen and an electronegative atom Major role in forming proteins individually weak and occur when atoms are close together but together they can be powerful Weak bonds are there to make the 3D shape of molecule function of molecule depends on shape depends on orbitals positions and determines how biological molecules recognizerespond to each other bond temporarily if shape is complementary Bonding rearranges electrons in orbitals Molecule with two elements is linear Molecules with s and p orbitals tetrahedron pyramid with triangular base gure is formed 0 H20 is shaped like a V with two covalent bonds with an angle of 1045 0 CH4 is a tetrahedron with carbon in middle and H shares all four orbitals makingbreaking of chemical bonds that lead to changes in matter Hydrogen and oxygen reactants form water product breaks bond of H2 and 02 and forms a new bond all atoms in reactant must be accounted for in product Greater concentration more frequently they interact with each other to form products Chemical equilibrium moment when reactions offset one another reactions still occur but no net effect on concentrations stabilized at ratio not speci c concentration
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