Atoms
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Who first discovered atomic theory?
Democritus, around 500BC, invented atomic theory, where everything is made out of atomos, which means indivisible particles.
What did Dalton discover?
John Dalton 1803, discovered that atoms of the same mass are the same material, and that atoms can compound to make new substances. He proposed that they were ‘solid spheres’
Who invented the plum pudding model?
JJ Thomson, in 1897, proposed the plum pudding model, where atoms are a ball of positive energy, dotted with the occasional electron for negativity.
What first major atomic development did Rutherford discover?
In 1909, Ernest Rutherford shot alpha particles at a thin sheet of gold. If the positive charge was truly spread out, all the particles would pass through. However, some alpha particles went off course or even deflected, disproving Thomson’s theory that the charge was evenly spread out.
What atomic model did Rutherford create?
Rutherford developed the nuclear model in 1917-1919, where the central, dense nucleus was positive, but was surrounded by negativity.
What did Bohr discover?
Niels Bohr suggested that electrons were on shells, orbiting the nucleus
What subatomic particle did Chadwick discover, and when?
He discovered the neutron in 1932.
How large is an atom and a nucleus?
The radius of the nucleus is less than 1/10,000 of the radius of the atom, surrounded by empty space. Size of an atom is around 1x10(-10)m to 5x10(-10)m. Almost all of the mass is centred around the nucleus. A hydrogen atom has a mass of 1u.
Who discovered atomic triads for the earliest periodic table?
Johann Dobereiner discovered that elements with similar properties often occurred in triads.
What did John Newlands theorise?
John Newlands developed octaves- by placing elements in mass order, every element shared properties with the element 8 spaces along. However, this method meant that some elements had no properties in common with others that they were associated with. Thus, his Law of Octaves was not successful
How did Mendeleev create the modern periodic table, and when?
Mendeleev created the first modern periodic table in 1869, by arranging elements in mass order, but then switching a few elements around to match up chemical properties, and missing some elements out, as he knew that they may not have been discovered yet. He even predicted the properties of these missing elements, and was proven right.
Which type of atom create positive ions, and which create negative ions, and why?
Metals form a positive ion when they react. Non metals either do not form ions at all, or form negative ions. This is because metals on the left have few valence electrons, making them easier to lose, while elements on the right have many valence electrons, so losing 6 or 7 requires too much energy and will not work.
Why are transition metals so useful in reactions?
Transition metals can form multiple ions, such as 2+, 3+ or 6+. They are also very good catalysts
Which group did Mendeleev’s table NOT include?
Noble gases
What happens with the boiling points of noble gases as you descend the group?
They increase
What happens when oxygen reacts with lithium?
The lithium’s edge goes dull. When reacting with oxygen, the lithium loses the outer electron, becoming a 1+ positive ion. Oxygen takes the electrons from two lithium atoms, becoming a 2- negative ion.
What happens as you descend the halogen group?
Melting points and density increase down the group. However, reactivity decreases.