Ch.2 Chem 111 STUDENT

Ch.2 Chem 111 STUDENT - C111 Eric C. Brown Ch. 2 Lectures...

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C111 Eric C. Brown Ch. 2 Lectures I. EVERYTHING IS MADE OF ATOMS - Atoms are the basic building blocks of matter; they are the smallest units of an element. - Need to understand the structure of the atom to explain chemical properties/reactivity. II. ATOMIC THEORY OF MATTER J o h n D a l t o n , E n g l i s h s c h o o lteacher (proposed 1803-1807) D e v e l o p e d t h e o r y t o e x p l a i n p r i o r e x p e r i m e n t a l o b s e r v a t i o n s - l a w o f c o n s e r v a t i on of mass (Lavoisier) - l a w o f c o n s t a n t c o m p o s i t i o n ( P r o u s t ) DALTON’S ATOMIC THEORY: ( A ) M a t t e r i s c o m p o s e d o f s m a l l , indivisible particles called a t o m s ( a t o m s a r e b a s i c b u i l d i n g b l o c k s ) (B) Atoms of a given element are identical ( h a v e s a m e m a s s , p r o p e r t i e s ) (atoms of different elements have diff. mass, properties) (C) Compounds are formed when 2 or more atoms combine ( i n a m o l e c u l e ) i n d e finite arrangements ( g i v e n c o m p o u n d a l w a y s h a s same # & kinds of atoms) 1
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C111 Eric C. Brown Ch. 2 Lectures ( D ) A t o m s o f a n e l e m e n t a r e n o t changed by chemical reactions ( n o t c r e a t e d n o r d e s t r o y e d ) , but are rearranged to form n e w c o m p o u n d s . III. STRUCTURE OF THE ATOM 1850s - New experiments questioned Dalton±s theory. - Experiments showed that the atom is made up of subatomic particles Æ atom is divisible - Subatomic particles ² electrons, protons, neutrons ELECTRON 1897 J.J. Thomson - Studied electrical discharge (high voltage generated cathode ray ) - D i s c o v e r e d t h a t t h e r a y w a s d e flected by the negative pole of an electric/magnetic field CONCLUSIONS OF EXPERIMENT - Ray consists of negatively charged particles Æ electrons. - Charge-to-mass ratio of electron determined = -1.76 x 10 8 C/g - Ratio is the same for every element! 1909 Robert Millikan - E x a m i n e d t h e m o t i o n o f c h a r g e d oil droplets in an electric field. C O N C L U S I O N S O F E X P E R I M E N T - C h a r g e o f a n e l e c t r o n = - 1 . 6 0 2 2 x 1 0 -19 C 2
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C111 Eric C. Brown Ch. 2 Lectures - Using the charge-to-mass ratio from Thomson, the mass of the electron was determined. e- = 9.10 x 10 -28 g - E l e c t r o n i s e x t r e m e l y small; ~1/1840 of a H atom PROTONS Atoms are electronically neutral , so an atom must contain an equal number of positive and negative charges. 1900 J.J. Thomson
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Ch.2 Chem 111 STUDENT - C111 Eric C. Brown Ch. 2 Lectures...

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