Periodic table and how the atom was formed Flashcards
Who made the plum pudding model
J J Thomson
When did Thomson discover his plum pudding model
1897
Explain Thomson’s plum pudding model
In 1897, an English physicist called J. J. Thomson discovered electrons.
Thomson modelled the atom as a ‘plum pudding’ - a ball of positive charge (dough), with negatively charged electrons (currants in pudding) mixed in with the ‘dough’.
Who created the nuclear model
Ernest Rutherford
Explain the nuclear model
In 1909, Ernest Rutherford discovered that alpha particles could bounce back off atoms.
Rutherford concluded that an atom’s mass is concentrated in the atom’s centre. This was called the “nucleus” and it contained positively charged particles called protons.
Who discovered the modern model
neil bohr
explain the modern model
Niels Bohr discovered that electrons orbit the nucleus at fixed distances.
what is an elements atomic number
the number of protons it has
where are protons found
in the nucleus
where are electrons found
in the fixed orbit around the nucleus
why do atoms have no overall charge
the total number of negative electrons equals the number of positive protons, meaning the charges cancel each other out
what is the relative mass of protons and neutrons
1
what is the relative mass of electrons
0.0005 which is rounded down to 0
how do you find the relative mass in atoms
number of protons+ the number of neutrons
how big are atoms
0.1 nanometres or 1x10 to the power of -10
compared to an atom, how big is the nucleus in an atom
10,000 times smaller
where is the mass number of an element found
at the top of the number
where is the atomic number found
at the bottom of the number
what is an isotope
an atom of the same element containing different number of neutrons
what is the relative atomic mass
the average mass of all of the isotopes of an element.
Who was the first scientist to devise a periodic table
John Newlands
How was Newlands table organised/ordered
by the mass (atomic weight) of elements
what was wrong with newlands table?
the table was incomplete and some elements were placed in inapropriate groups, elements in some groups did not react similarly with each other
Explain Dimitri Mendeleevs periodic table
- Dmitri Mendeleev recognised that there may be undiscovered elements.
Mendeleev added gaps to Newlands’ table to account for undiscovered elements. - He also predicted the properties of these undiscovered elements and several years later, when these elements were discovered, their properties matched Mendeleev’s predictions
- He also changed the order of elements based on their atomic weight
- if he needed to, he would switch the order of specific elements, so that they fitted the patterns of other elements in that group
briefly describe the role John Newlands played in the history of the periodic table
- he ordered elements in increasing atomic weight
- he saw that every eighth element reacted in a similar way (this was called the law of octaves)
What discovery proved Mendeleev’s periodic table to be correct and Newlands’ to be wrong
the discovery of protons and isotopes
where are metals found on the periodic table and why
they are found on the left side of the table because they have few electrons in their outer shell
what did James Chadwick discover
In 1932, James Chadwick discovered that some particles in the nucleus have no charge at all. He called them neutrons.
summarise the alpha particle scattering experiment
- ernest rutherford fired positively charged alpha particles at thin sheet of gold
- most particles went straight through, some deflected, and some deflected backwards
what conclusions were made from rutherfords experiments
- most of the atom is empty space
- in the atom, there is a tiny, positively charged nucleus where most of the mass is concentrated, when alpha particles came in contact with it, they deflected
- if fired directly at the nucleus, they deflect backwards, otherwise they just pass straight through
why was gold used for the alpha scattering experiment
because we can hammer gold into a very thin sheet, only a few atoms thick
what charge are alpha particles
positive
what are ions
atoms with an overall charge
what do all elements in a group have
- similar chemical properties
- they react in a similar way as they have the same number of electrons on their outer shell
differences between Mendeleev’s periodic table and the new one
- in the modern periodic table, elements are arranged in order of atomic number (number of protons), and when Mendeleev discovered his table, protons had not been discovered yet, so he ordered them by atomic weight
- The modern periodic table contains group 0, which had not fully been discovered when Mendeleev published his
what is atomic weight
relative atomic mass
one problem with Mendeleev’s table
he arranged elements in order of atomic weight, meaning that elements can appear in the wrong order due to the presence of their isotopes
