Atomic theory 3 (history)

What were the assumptions in rutherfords nuclear model of the atom

• atoms are composed of small dense positive core called the nucleus, the mass is mainly in the nucleus

• positive protons are found in the nucleus

• atoms are mainly empty space

• electrons are in an electron cloud found around the nucleus, how they move was not described

what were the limitations of the nuclear model proposed by rutherford

• how does the nucleus not come apart if protons repel each other

• why aren’t negative electrons attracted into the positive nucleus

what was chadwick’s updated nucleur model

• atoms are composed of a small dense positive core called the nucleus

• positive protons and neutral neutrons are found in the nucleus 

• atoms are mainly empty space 

• electrons are in an electron cloud 

what did dobreiner do

• noticed there were groups of three elements with similar prooperties

• atomic weight of one of these elements was midway between the other two

• called these triads

what did newlands do

law of octaves - listed elements known at the time in order of increasing atomic weight worked for first 16, this was important as it showed elements had periodic properties

why didnt htey know about noble gasses

unreactive, colourless,odourless

wjat did mendeleev do

listed elements in order of weight, similar properties under eachother, left gaps for undiscovered elements, reversed order of pairs so listed in groups of similar properties

what did mosely do

• nucleus of each element contained positive charge of a definite amount 

• atomic number 

differences between modern table and mendeleevs table

• mendeleevs table had no noble gasses

• was in increasing atomic weight (not number)

• mixed transition elements with others

what did democritus say

matter composed of small indivisable particles, called atoms

what did dalton say

• matter made up of indivisable atoms

• atoms in a given element are identical in mass and properties

• atpms cant be created or destroyed in a chem reaction

• atoms combine to form compounds that are different from the atoms which they were formed

crookes did what

concluded cathoe rays made up of particles coming from cathode, travelled in a straight line and were negatively charged

whats an negative electrode called

cathode

whats a positive electron called

anode

how did crookes see his electtrons 

cast a shadow when an object was placed in their path

what did stoney do

name cathode rays electrons

cathode rays were

invisable, travelled in a straight line, negative charge

what did thompson do

• credited with discovery of first subatomic particle

• plum pudding model, positive sphere with negative electrons embedded in it in a random fashion

what is the plum pudding model

positive sphere with negaitve electrons embedded in it 

what did millikan do

measured size of charge of electrons using oil drop experiment

what did rutherford do

gold foil experiment

what happens in the gold foil experiment (procedure)

bombarded extremely thin gold foil with alpha particles

what did rutherford expect

for all the alpha particles go straight through

what actually happened in the gold foil experiment

1. most particles went straight throughm showing atoms must be made up of empty space

2. some alpha partilcles passed through but were deflected at large angles

3. very few bounced back

what did rutherfords experiments prove

that there are is a small positive dense core to the atom called the nucleus

the positive particles in the nucleus are called protons

what did rutherfords experiments allow him to conclude about nucleuss and why

• small, such a small number of alpha particles reflected or deflected by nucleus

• positive - positive alpha particles were REPELLED by the nucleus

• dense, particles BOUNCED back