C4 Flashcards
What did john Dalton say about atoms in the 19th century?
They were solid spheres and different ones made up elements
What did jj Thompson ten say about atoms in 1897?
That they were not solid spheres. His measurements of charge and mass showed at atom must contain smaller negatively charged particles- electrons
What was the name of the theory that came after the solid sphere idea?
The plum pudding model
What did Rutherford prove wrong?
The plum pudding model
How was the plum pudding model proved wrong./
Rutherford conducted the gold foil experiment where positively charged particles were fired at a very thin sheet of gold. Most of the particles passes straight through and a small number bounced back. This showed the plum model was incorrect as according to that the particles would be defected back.
What was rutherfords idea?
That the nuclear atom. There is a tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons. Most of the atom is empty space
What did bohr add to the atom theory?
The idea that the electrons were not a cloud but in shells. They exist in fixed orbits and each shell has a fixed energy.
Why were ideas of atoms accepted?
Because they fitted the evidence available at the time. As more experiments were carried out the theories of atoms and structure was modified to suit. More scientific knowledge means improved ideas and predictions
What is peer review?
Everyone gets a chance to see new ideas and check them for errors, this helps scientists develop ideas and work
What is the nucleus in an atom/ properties?
It’s in the middle and contains protons and neutrons, it has a positive charge due to the protons. Almost the whole mass of the atoms is concentrated in the nucleus
What are the electrons in an atom/ properties?
Move around the atom in shells. They are negatively charged. They are very tiny but cover a large amount of space. The volume of their orbits determines the size of the atom. The have virtually no mass
What’s a proton/
They are heavy and positively charged
What’s a neutron?
They are heavy and neutral
What’s an electron?
They are tiny and negatively charged
Why do neutral atoms have no charge?
Because they have the same number of protons and neutrons. The charges cancel each other out.
What does the atomic number tell you?
The number of protons ( the bottom number)
What is the mass number?
The total number of protons and neutrons ( the top number)
How can you calculate the number of neutrons?
Subtract the atomic number form the mass number
What is an isotope?
A different form of the same element which has the same number of protons but a different number of neutrons
What does an isotope have the same a different?
Same atomic number but different mass numbers
How can you remember the history of the periodic table?
Dobby likes triangles but newlands came along and rearranged dobby triangle’s into octagon. Mendeleev came along and mended the periodic table and left. He came and left gaps.
What did dobereiner do to the periodic table?
He organised the elements into triads. And groups based on chemical properties. He put them into groups of three. The middle element of each triad had a relative atomic mass that was average of the other two.
what did newlands notice about the elements?
every eights element had similar properties and so he listed the known elements in rows of 7.
why did newlands octaves not work?
the pattern broke down on the third row as transition metals like titanium and iron messed it up and did not fit. he aso lef no gaps so his work wa ignored.
why was newands ideas criticized?
his groups contained elements that did not have similar properties ( carbon and titanium)
he mixed up metals and nonmetals
he did not leave any gaps for new elements
what did dmitri mendeleev do to the perodic table
he organized the known 50 elements into a table with gaps for new ones. he put them in order of atomic mass like newlands but he left gaps to keep elements with similar properties in the same vertical groups.
what are the 3 rules for electron shells?
electrons always occupy shells/ energy levels
lowest energy levels filled first
only a certain number of electrons allowed in each shell
how many electrons are allowed in each shell
1st shel: 2 electrons
2nd shell : 8
3rd shell: 8
define ionic bonding
transferring electrons
in this bonding atoms lose or gain electrons to form charged particles or ions which are then strongly attracted to each other.
if an atom has an outer shell with just one electron what is it keen to do?
get rid of it and lose them so they can have a complete outer shell. they become positive ions
if an atom has a nearly full out shell of 6/7 what is it keen to do/
to gain an extra electron or two to complete their shells . they become negative ions
what kind of structure do ionic bonds have
giant ionic lattices. the ions are closely packed together in a regular lattice arrangement. the ions are not free to move so the compounds do not conduct electricity when slid. they are very strong
what makes magnesium oxide and sodium chloride have high melting and boiling points?
they have very strong attraction forces between oppositely charged ions in the giant lattice structures. to break the bonds you have to overcome these attraction forces and this take allot of energy
when metal form ions they…
lose electrons and form positive ions
when non metals form ions they…
gain electrons and form negative ions
what happens when a metal and a non mental combine.
they form ionic bonds
if a electron is gained will it become negative or positive
negative
if an electron is lost will it become negative or positive
positive
what a covalent bond?
sharing an electron
when are covalent bonds formed/?
when non metals combine they share their electrons to complete both their outer shells
