1. I. All elements are composed of bantam indivisible atoms called atoms. 1. two. Atoms of the same component are indistinguishable. The atoms of any one component are different from those of any other component 1. three. Atoms of different elements can physically blend together or can chemically unite in simple whole-number ratios to organize compounds 1. four. Chemical reactions occur when atoms are separated from each other. joined. or rearranged in a different combination. Atoms of one component. nevertheless. are ne’er changed into atoms of another component as a consequence of a chemical reaction.
Sizing up the Atom Atoms are really little the radii of most atoms fall within the scope of 5 ten 10^-11 m to 2 ten 10^-10m atoms can be seen in scanning negatron microscopes atoms can be moved 4. 2 Structure of the Nuclear Atom Overview Lots of Dalton’s theory is accepted except that atoms can be divided Atoms can be divided into three subatomic atoms Protons Neutrons Electrons Subatomic Particles Electrons Discovered by UK physicist J. J. Thomson ( 1856-1940 ) Are negatively charged subatomic atoms. Thomson’s Experiment passed electric current through gasses at low force per unit area.
Sealed the gases in glass tubings fitted at both terminals with metal discs called electrodes electrodes connected to beginning of electricity one electrode called the anode became positively charged other electrode. called cathode. became negatively charged resulted in glowing beam called “Cathode Ray” that traveled from cathode to anode. Findingss cathode beam is deflected by electrically charged metal home bases positively charged home base attracts the cathode beam negatively charged repels it Thomson knew that opposites pull hypothesized that a cathode beam is a watercourse of negatively charged atoms traveling at high velocity called atoms “corpuscles” .
Subsequently called “electrons” Millikan’s Experiment US physicist Robert A. Millikan ( 1868-1953 ) carried out experiments to happen the measure of an electron’s charge. Oil bead experiment suspended negatively charged oil droplets between two charged home bases. so changed electromotive force on the home bases to see how it affected the droplets’ rate of falling he found that the charge on each oil droplet was a multiple of 1. 60 ten 10^19 C intending it was the charge of an negatron calculated electron’s mass Millikan’s values for negatron charge and mass are similar to those accepted today.
An negatron has one unit of negative charge and its mass is 1/1840 the mass of a H atom Protons and Neutrons Four simple thoughts about affair and electric charges 1. Atoms have no net electric charge ; impersonal 2. Electric charges are carried by atoms of affair 3. Electric charges ever exist in whole-number multiples of a individual basic unit ; that is. there are no fractions of charges. 4. when given a figure of negatively charged atoms combines wit an equal figure of positively charged atoms. an electrically impersonal atom is formed.