Atomic Structure UNIT 1 Flashcards
Relative mass and charge of a neutron
Mass…..1
Chase……0
Relative mass and charge of a proton
Mass…. 1
Charge….. +1
Relative mass and charge of an electron
Mass……. 1/2000
Charge…….-1
All atoms of the same element have the …….. Number of protons
SAME
Neutral atoms have the same number of what?
Protons and electrons
What makes an atom neutral
Having the same number of electrons and protons
Isotopes can have different physical properties such as……. Why?
Different densities, rates of diffusion
Physical properties depend more on the mass of the atom
Define relative isotopic mass
Mass of an atom of an isotope of an element compared with 1/12 the mass of carbon12
Electron shells are made up of…
Sub-shells and orbitals
Each electron shell is given a number called what
Principal quantum number
What does it mean the energy shell is further from the nucleus
The higher it’s energy and the larger it’s principal quantum number
The two electrons in each orbital spin in the…..
Opposite direction
Which sub shell fills first…3d or 4s? Why?
4s because it has a lower energy level than 3d, even though it’s principal quantum number is bigger
Examples of transition metals acting unusually
Cr and Cu donate one of their 4s electrons to the 3d sub shell, as they are happier with a more stable full or half full d sub shell
When they become ions they lose their 4s electrons before their 3d electrons
The number of outer shell electrons decides the ………. ……..
Chemical properties
Number of Outer shell electrons in group 1and 2 (s block) elements
1 or 2, these are easily lost to form positive ions with an inert gas configuration
Number of electrons in groups 5,6 and 7 (p block)
5,6 or 7 outer electrons. They gain 1,2 or 3 electrons to form negative ions with an inert gas configuration. Groups 4-7 can also share electrons when they form covalent bonds
Number of outer electrons in group 0 ( the inert gases)
Have completely filled s and p sub shells so don’t lose or gain electrons, their full sub shells make them inert
Number of outer electrons in d block (transition metals) elements
2 electrons, tend to lose s and d electrons to form positive ions
What did John Dalton describe atoms as in the 19th century
Solid spheres, different spheres made up different elements
What was J J Thompson’s theory in 1897
He concluded from his experiments that atoms weren’t solid and indivisible. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles-electrons . The solid sphere idea had t be changed, the new model was called the ‘plum pudding model’
What did Rutherford show
That the plum pudding model was wrong
What was rutherfords experiment
It was called the gold foil experiment. They fired alpha particles (which are positively charged) at an extremely thin sheet of gold. From the plum pudding model, they were expecting most of the particles to be deflected very slightly by the positive ‘pudding’ that made up most of the atom. But most of the particles passed straight through the gold atoms, very small number deflected backwards. So plum pudding couldn’t be right. Rutherford came up with the nuclear model of the atom. In this there is s tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons, most of the atom is an empty space.
What did scientists discover was wrong with rutherfords model
They realised that electrons in a cloud around the nucleus of an atom would quickly spiral down into the nucleus causing the atom to collapse
What did the Bohr model propose
Electrons can only exist in fixed orbitals, or shells, and nowhere else
Each shell has a fixed energy
When an electron moves between shells electromagnetic radiation is emitted and absorbed
Because the energy of shells is fixed, the radiation will have a fixed frequency
What is one of the things that makes a theory scientific
If it’s ‘falsifiable’. You can make predictions using the theory, then if you test the predictions and they turn out to be wrong, you know the theory is wrong
What did scientists find wrong with the Bohr model
Not all the electrons in a shell had the same energy. So they refined it to include sub shells
How did the Bohr model explain why some gases are inert
Bohr said that the shells of an atom can only hold fixed numbers of electrons, and that an elements reactivity is due to its electrons. So when an atom has full shells of electrons it’s stable and doesn’t react.
Is there only one accepted model of the atom today
No, Bohr model is not perfect but is still widely used to describe atoms because it is simple and explains many observations from experiments, like bonding and ionisation trends. The most accurate model involves complicated quantum mechanics. Explains the direction that the electron is moving in and how they can also act aaa waves . This may be more accurate but harder to visualise, does explain some observations that can’t be accounted for by the Bohr model. Scientists use whichever model is most relevant to whatever they’re investigating.
