Atomic Structure Flashcards
What did John dalton a atomic theory say?
All matter is made up of tiny particles called atoms
Atoms are tiny, hard spheres that cannot be broken down into smaller parts
Atoms cannot be created or destroyed
The atoms in an element are all identical (but each atom has its own type of atom)
What did dalton so ideas help explain?
Some of the properties of matter. However experiments towards the end of the ninetieth century suggested that atoms contain even smaller particles
When high voltage is applied to a glass tube that has most of the air removed what is seen?
Glowing rays
What did some scientists think that cathode Ray’s were?
Atoms leaving the negative electrode
In 1897 what did JJ Thompson (1856-1940) investigate?
The mass of the particles in the Rays and found that they were about 1800 times lighter than the lightest atom (hydrogen)
What did cathode rays contain instead of atoms?
Subatomic particles, which we call electrons
Scientists have now worked out that atoms are made up of electrons together with heavier subatomic particles, they are called?
Protons and neutrons
What do electrons, protons and neutrons have?
Very very, small masses and electric charges, so rather than use their actual masses and charges, it’s easier to describe them by looking at their relative masses and relative charges, compared to a Proton
What happens if we say the mass of a proton is 1?
Then anything else that has the same mass is also 1
What are the 3 subatomic particles?
Protons, electrons, and neutrons
Look at page 18
And look at the table
What is at the centre of all atoms and what is it surrounded by?
A tiny nucleus containing protons and neutrons and its surrounded by fast moving electrons arranged in electron shells at different did ranches from the nucleus
What do atoms in elements always have?
Equal numbers of protons and electrons and so have no overall charge because the charges cancel out
Go to page 19 and look at the diagram
Do it
What do models of atoms help us understand?
Their structure - but most models don’t really give a correct impression of the scale. The overall diameter of an atom can be 100000 times the diameter of it nucleus
In 1909 Ernest Rutherford (1871 - 1937) what was she working with other to investigate?
The structure of atoms
What was an experiment Ernest Rutherford carried out and what happened)
The gold foil experiment, tiny positive particles were fired at a thin gold foil, to everyone’s surprise most of the particles passed straight through the gold foil, with a few being deflected and a very small number bouncing back
How did Rutherford explain the gold foil experiment?
By suggesting that atoms are mostly empty space, with a small positive central nucleus that contains most of the mass
When did the English chemist John dalton publish his atomic theory?
1805
What order in the periodic table were originally placed?
In order of the masses of their atoms
What was the problem with the elements being placed in order of heir masses and what did they do?
This caused elements to be grouped with others that had very different properties so a few elements were swapped around to make sure those with similar properties were grouped together, even if it meant they were no longer in the correct order of mass
What did the experiments by Henry Moseley (1887 - 1915) confirm and what did he show?
That the rearranged order of the elements in the table were actually correct. He showed that they were in order of the amount of positive charge in he nucleus
When was the proton discovered?
In 1913 Henry Moseley confirmed that the rearrange order of the elements were correct, the proton was discovered about 5 years later
Were does the modern periodic table place the elements?
In order of the number of protons in their atoms, this is the atomic number and it is this that defines an element - all the atoms of a particular element have the same unique atomic number
What is the mass of an electron described as and what does it explain?
Negligible - it is so small it can be ignored. This explains why the nucleus of any atom contains nearly all its mass
What is the total number of protons and neutrons in an atom called?
It’s mass number
What is the mass number and the atomic number represented by?
A mass number is represented by the symbol A and an atomic number by the symbol Z. These numbers are written next to an elements symbol
Turn to page 21
And look at diagram b
In 1932 what did James Chadwick (1891-1974) Discover and what did this explain?
He discovered the neutron and his discovery explains why some atoms of the same element have different masses
What are some atoms of the same element that have different ,asses called?
Isotopes
What do isotopes have?
The same atomic number but different mass numbers
How do we refer to a specific isotope?
By adding it’s mass number to the elements name
Turn to page 22
And look at diagram a
What did understanding neutrons lead to?
The discovery of nuclear energy
By firing neutrons at a uranium isotope what was discovered?
That a nucleus can be split (nuclear fission)
What does nuclear fission produce?
New elements and transfers large amounts of energy. Nuclear power stations use the energy from nuclear fission to produce electricity
The mass of an atom is incredibly small, so how do measure their masses?
We measure their masses relative to (compared to) -12
Turn to page 23 and look at
Relative atomic masses
What is the relative mass of an isotope ?
It is it’s mass number
What do all elements exist as?
A mixture of isotopes
What idea do we use to calculate an elements relative atomic mass (RAM)?
That all elements exist as a mixture of isotopes
What is a relative atomic mass?
It’s the mean mass of an atom of an element compared with -12. This takes into account all the isotopes of the element and the amounts of each
What are RAMs not?
Whole numbers but most values are commonly rounded to whole numbers. The ram of an element and its atomic number are shown on the periodic table
Describe how Daytona ideas about atoms have changed
Dalton said that all matter is made up of tiny particles called atoms, atoms are tiny hard spheres that cannot be Brocken down into smaller parts, atoms cannot be created or destroyed, the atoms in an element are all identical (but each element has its own type of atom)
However experiments towards the end of the 19th century suggested tag atoms contain even smaller particles
How are the subatomic particles arranged in an atom?
At the centre of all atoms is a tiny nucleus containing protons and neutrons. This is surrounded by fast moving electrons arranged on electron shells at different distances from the nucleus
Explain how atoms of different elements are different?
Because each different element has a different atomic number
Turn to page 18
And look at the table
Why do atoms have no overall charge?
Because atoms in elements always have equal number of protons and electrons and so have no overall charge because the charges cancel out
How does the size of the nucleus differ to the size of an atom?
The nucleus is much smaller than the atom
Where is most of the mass of an atom found?
The nucleus of any atom contains nearly all its mass
What is the meaning of atomic number?
The atomic number is the thing that defines an element, it is the proton number
What is the mass number?
The total number of protons and neutrons in an atom
How do the atoms of different elements vary?
The amount of neutrons vary
State the number of electrons in an atom from its atomic number
The amount of electrons equals the amount of protons which is the the atomic number
What is an isotope?
They have the same atomic number but different mass numbers
Why is the relative atomic mass not a whole number?
RAMs are not always whole numbers but they are rounded to whole numbers
Turn to page 23
And look at the H box
How do you identify isotopes?
They will have a different mass number
