Ch.2-Atomic Structure Flashcards
What was John Dalton’s atomic theory?
In 1808, Dalton said,
1. All matter is composed of small indivisible particles called atoms.
2. Atoms of a given element are identical to each other in size mass and other properties. Atoms of different element vary in size, mass and other properties.
3. Atoms cannot be created or destroyed.
4. Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
5. In chemical reactions, Atoms are combined, separated or rearranged
What experiments did William Crookes carry out?
William Crookes carried out several experiments in a vacuum tube. In the Maltese Cross experiment, he placed a Maltese Cross in a vacuum tube and passed electricity through the tube. A shadow in the shape of the Cross was cast on the opposite side of the tube to the cathode. This proved that radiation was coming from the cathode. The rays, that we understand today as electrons, were known as cathode rays. He also proved that these cathode rays had enough energy to turn a paddle wheel.
What experiment did J.J. Thomson carry out?
In 1897, Thomson carried out an experiment with a cathode ray tube containing a pair of oppositely charged, parallel vacuum tubes. The cathode rays were attracted towards the positive plate, so the particles must be negatively charged.
What are cathode rays?
Cathode rays are streams of electrons. They are negatively charged and have enough energy to move a paddle wheel. They move in straight lines from the cathode to the anode and can be deflected by electric and magnetic fields.
Who discovered electrons?
J.J. Thomson named the particles from cathode rays as electrons. This was a name suggested by Johnstone Stoney.
How did Thomson calculate e/m?
Cathode rays are deflected by magnetic fields. Thomson used this property to measure the ratio of charge to mass (e/m) for cathode ray particles.
What did Thomson’s plum pudding model consist of? Who disproved this theory?
Thomson’s plum pudding model consisted of electrons suspended in a spherical cloud of positive charge. Rutherford’s discovery disproved this model.
What experiment did Robert Millikan conduct?
In 1911, Millikan carried out the oil drop experiment. Oil was sprayed in a fine mist. X-rays were used to knock electrons out of the air. The oil droplets picked up these electrons, becoming negatively charged. The charge was altered until the droplets floated; the force of the charge = the force of gravity. This allowed him to calculate e (the charge) and m (the mass) of the electrons.
What experiment did Ernest Rutherford carry out?
Rutherford discovered the nucleus by bombarding gold foil with alpha particles (+ve charged) and looking at what happened to them.
What were the results of the Gold Foil experiment?
Most particles passed straight through because matter is mostly empty space. Some were deflected at large angles because +ve particles repelled when passing near the positive nucleus. A few particles were reflected back along their original path because the +ve particles collided head on with the nucleus.
How did Rutherford discover protons and what resulted?
Rutherford discovered protons by bombarding elements lighter than gold with alpha particles. These would break up, releasing small positively charged particles called protons. The atomic number and the Bohr model resulted from this discovery.
What did Moseley do?
Moseley discovered atomic numbers using x-rays. Moseley arranged the elements in the periodic table according to their atomic number.
Who discovered the neutron and how?
James Chadwick discovered the neutron by bombarding beryllium nuclei with alpha particles. Neutrons were released.
What does the atomic number reveal?
The number of protons in the nucleus of an element.
The number of electrons in an element.
The position of that element in the periodic table.
What are isotopes?
Isotopes are elements of the same atomic number but with different mass numbers.
